first time from the north. This will explain many of the peculiarities of the Palearctic, Oriental, and Ethiopian regions, and of their several sub-regions, and especially the persistence of low types in those districts which were wholly or partially protected from the competition of more highly organized animals. The Tertiary fauna of North America compared with that of Europe exhibits proofs of a former communication between the two Lorthern continents both in the North Atlantic and North Pacific, but always, probably, in rather high latitudes. This is indicated both by the groups which appear to have originated in one continent and then to have passed across to the other, and also by the entire absence from America of many important groups which abounded in Europe (and vice versa), indicating that the communication between the two hemispheres was always imperfect and of limited duration. The past zoological history of North and South America exhibits a somewhat analogous series of phenomena. Their productions were generally very dissimilar. North America, in closer connection with the great northern continent, made an almost equal advance in the development of the more highly-organized animals; while South America, for the most part isolated and thus prevented from receiving a constant supply of immigrants from the larger land-areas, developed a series of lowly-organized creatures, the smaller forms of which still constitute its chief zoological feature. The knowledge we possess of Tertiary and post-Tertiary Mammalia thus gives us an important clue to the successive migrations of the various groups of animals from one region to another, and to the geographical changes which rendered such migrations possible. The general result arrived at is, that the great northern continents represent the original seat of mammalian life, and the region of its highest development; while the southern continents-Australia, South America, and Africa-have been isolated for varying periods, and, after receiving an immigration of lowly forms, have developed and preserved these to a greater or less extent, according as they were more or less completely protected from the irruption and competition of higher types. Australia, during the Secondary period, received from the northern continent a stock of Marsupials and perhaps some still lower forms, and, having been since completely isolated, has developed these groups alone into its existing fauna. South America, at a somewhat later period, obtained the ancestors of its Edentata and Rodents; and though at various times some higher forms entered it from the north, these never seem to have been sufficiently numerous to overcome its indigenous fauna. In Africa the case was different. For a long time its Mammalia were probably analogous to those of South America; but when the great irruption of higher animals took place in the latter part of the Tertiary period, most of these were destroyed, and a few only remain-such as the Orycteropus, the Lemurs, and the peculiar Rodents-as indications of the character of the primeval fauna. In the peninsula of India a very similar course of events occurred, and the fauna of both these countries now consists mainly of comparatively recent immigrants. (For a fuller discussion of this subject see Wallace's Geographical Distribution of Animals, chapters vi. to xv.) The Birth-place and Migrations of some Mammalian Families and Genera. From the knowledge we now possess of the extinct fauna of most of the great continents, it is possible to determine approximately the original birthplace of some now widely distributed groups. The true bears, for example, date back in Europe to the older Pliocene, while in North America they occur only in postPliocene deposits. We may conclude, therefore, that they originated in the Old World and are comparatively recent immigrants in America. True horses of the genus Equus are also of older Pliocene date in Europe and of the postPliocene, or perhaps newer Pliocene, in America, and are therefore also recent immigrants into the latter country. But it is a curious fact that the most perfect series of ancestral forms of horses occur in the Miocene and Eocene deposits of North America; whence it would seem probable that the earlier stages of the development of this wonderfully specialized animal were effected in America, whence they passed to the eastern hemisphere, and there attained to the full development of the equine type, again, perhaps, to be transferred to America,-to be largely developed there (for remains of eight or ten distinct species have been discovered), and finally to become wholly extinct, while continuing to exist in the Old World, whence the most perfect form has been again introduced, and seems quite capable of maintaining itself in a wild state. Tapirs, though now more abundant in America than in Asia, are an Old World group, going back to the Lower Miocene in Europe, but only appearing in America in the post-Pliocene epoch. The peccaries Dicotyles), now almost wholly Neotropical, are really a North American group, and probably only entered South America in later Pliocene times. Camels, though now confined to Asia and South America, are really a North American form, having been largely developed during the Miocene period, whence the true camels appear to have passed into Asia and the llamas into South America. True deer are European from Miocene times, but only appear in America in the later Pliocene and post-Pliocene epochs. Elephants are an Old World type, abounding from the Miocene period in Europe and Asia, but only appearing in America in the later Pliocene and post-Pliocene times. It is possible, however, that the Eocene Dinocerata of North America may be ancestral forms of Proboscidea, and that, as in the case of the horses, the development of elephants may have begun in America to be subsequently perfected in the larger area of the eastern hemisphere. As a last and curious example we may refer to the marsupial opossums, now exclusively American, but which are certainly recent immigrants from Europe or Asia. No trace of them occurs in American deposits before the post-Pliocene period, while they existed in Europe both in Eocene and Miocene times. The cases now adduced are sufficient to show how much interest attaches to the distribution of the ancestral forms of our existing animals; but we wait for fuller knowledge of the Tertiary deposits of Asia, Africa, and South America in order to complete the history of these migrations, and to gain some knowledge as to many other groups whose origin is now involved in obscurity (Geog. Dist. of Animals, vol. i. p. 153.) DISTRIBUTION OF MARINE ANIMALS. The zoological regions which serve to represent the main facts of the distribution of land animals are evidently inapplicable to those inhabiting the ocean, except in a few cases where the group is confined to shallow waters or to estuaries. It is true that, as the great continents are separated by the oceans, so the oceans are to some extent separated by the continents, but owing to the superior area of water the separation is far less complete and effective. In the southern hemisphere the Pacific, Atlantic, and Indian oceans freely communicate and for truly oceanic animals there would seem to be hardly any obstacle against universal distribution. Yet even in this case physical conditions, especially depth and temperature, are found to be effective barriers. The fact that the deep waters even of the tropical seas are cold, renders it indeed possible for some temperate or Arctic forms to cros the equator if they can travel at great depths; but for sur face-dwellers the broad expanse of warm water between the tropics, with its hosts of specially adapted organisins, forms an absolute barrier. In like manner the inhabitants of the tropical shallow waters are limited, and it is only by temporary subsidences of land or elevations of the sea-bottom to near the surface, allowing of a passage east or west, that they can migrate into remote areas. We have good reason to believe, however, that subsidences have often occurred between North and South America, allowing of a free interchange of aquatic animals between the Atlantic and Pacific oceans; while in Eocene times a strait is supposed to have connected the Atlantic and Indian oceans, and more recently the Red Sea and Mediterranean have almost certainly been united. We cannot, therefore, expect to find any such strongly-marked zoological regions among aquatic as among terrestrial animals, and the facts at our command entirely confirm this view. For many groups the warm and the cold, or the northern, tropical, and southern seas, are the only well-marked divisions; while for others the North Atlantic, the North Pacific, and the Indian Ocean form additional regions of a more or less defined character. For special studies of the more highly-organized marine groups-as the Mollusca or Crustacea-a host of provinces and sub-provinces have been formed, each important sea or coast presenting some peculiar features; but as these divisions mostly depend on specific rather than generic distribution, they need hardly be noticed here. Owing to the absence of any well-marked regions, and the general imperfection of our knowledge of the distribution of marine animals, we must follow a different plan in our sketch of this subject from that adopted for the terrestrial fauna. We propose, then, to notice successively the more important classes of marine animals, and to state briefly what general facts are established as to their distribution. Foraminifera.-These exceedingly low organisms are important, because their shells or tests are found extensively in various geological formations, and often form a considerable part of the constituents of rocks. They are found in all seas, and the species have often an enormous range. The surface swimmers are almost universally distributed, while the bottom-livers-as the writer is informed by Mr H. B. Brady-appear to be distributed according to depth and latitude rather than to follow any circumscribed areas. This gentleman is now engaged in working out the "Challenger" collections, and already sees reason to think that there may be found some differences between Atlantic and Pacific, and also between North Atlantic and South Atlantic forms. These organisms have been found living in the surface waters and down to a depth of 2000 fathoms, but only their dead remains are brought up from the floor of the deep ocean. Spongida.-Sponges form another extensive group, often preserved as fossils, of which our knowledge of the recent forms is rapidly increasing. There seems, however, to be little geographical limitation of groups. The fresh water Spongillida are found in all regions. The horny and calcareous sponges are widely distributed, but are much more abundant in warm and tropical seas. The beautiful siliceous sponges of which the glass-rope (Hyalonema) and Venus's flower-basket (Euplectella) are conspicuous examples-are found scattered throughout all warm seas, and have recently been found in abundance in many of the great ocean depths.-in the Atlantic at 2650 fathoms, and in the Pacific at 3000 fathoms,- -so that they probably exist wherever the nature of the bottom is favourable. (Sir Wyville Thomson, Depths of the Sea: "Reports from the Challenger,'" Proc. Roy. Soc., vol. iv.; Bowerbank's "Papers on Sponges" in Proceedings of Zoological Society, 1869-1874.) | Actinozon. The coral-bearing groups of these aninials are the more important, because of the abundance of fossil forms of every geological age. By far the greater number of these are found exclusively in tropical seas. Many of the Alcyonaria are temperate and even Arctic, while among the Zoantharia the Caryophyllide alone are well represented beyond the tropics. The distribution of corals is in great part determined by the physical conditions of the seabottom. An influx of fresh water or of mud brought down by rivers is fatal to them, and volcanic deposits seem to be almost equally prejudicial. A high temperature is also necessary for most of the groups. Coral reefs are therefore restricted to certain seas and coasts within or near the tropics. They abound in and near the West Indies, on the east coast of Africa, in the Indian Ocean, in the Malay and Pacific archipelagoes, and on the coast of Australia; while they are absent from the whole of the west coasts of South America and of Africa, from the Indian peninsula, and from much of the east coast of South America. The coral-reefs of the Bertnudas, in 33° N. lat., are the farthest from the equator; in the Red Sea they reach 30° N., in the Pacific 27° N., while they nowhere extend to more than 29° S. of the equator. Besides the corals actually forming the reefs, the same localities abound in what are termed deep-sea corals, and thus the general distribution of the group is determined by similar conditions. The coral regions are therefore somewhat peculiar, and differ considerably from those which best exhibit the distribution of other marine animals. The regions adopted by Mr Dana are three,-the first comprising the Red Sea and Indian Ocean; the second, the whole of the Pacific islands and the adjacent coasts of Australia; and the third the West Indies. This last region is the most isolated in position, and it is not surprising that it should contain the largest proportion of peculiar forms. The corals of the Central Pacific are also very peculiar, as are those of the Red and Indian seas. Considering the great similarity of the molluscan fauna of the Pacific and Indian oceans, it is remarkable that the corals should be so different as Mr Dana's tables show them to be. Although some corals exist at great depths in the ocean, they diminish rapidly when we pass the moderate depth of 200 fathoms. Tho "Challenger" expedition obtained 27 genera at a greater depth than 250 fathoms, but only 3 of these extended below 1500 fathoms. Count Pourtales on the American coast found them at 400 fathoms; the "l'orcupine expedition first found them at a greater depth than 1000 fathoms in the North Atlantic; while in the Pacific a single species has been found at the enormous depth of 2900 fathoms. The following genera were obtained by the "Challenger" dredgings at a greater depth than 1000 fathoms :-Caryophyllia, Deltocyathus, Ceratotrochus. Flabellum. Ampkehelia, Cryptohelia, and Fungia. Some of these were of brilliant colours-pink, madder-red. white. and emerald green. A large proportion of fossil genera of corals survive in the deep seas, no less than seven genera, before only known in the fossil state, having been added by the explorations of the "Challenger ;' seven of these are found at or below 1000 fathoms. It is curious, however, that the deepest by far of all corals, Fungia, is not known to be fossil, nor is any member of the family Stylasteridæ, six genera of which are deep-sea corals; o that too much importance must not be attached to the fact of genera hitherto only known as fossils having been found living at great depths in the ocean. (Dana's "Zoophytes" in U.S. Exploring Expedition, vol. vii.; “Report on Corals Dredged by the Challenger,'" by H. N. Moseley, Proc. Roy. Soc., vol. xxiv. p. 544.) Polyzoa. The coral-like Molluscoida forming the extens sive group of marine polyzoa, have been carefully studied, but they are so widely distributed as to offer few special features of distribution. One or two families--as the Selenariado are almost exclusively tropical; others as the Catenicellido and Vinculariado-are confined to the southern hemisphere. The Diastoporide are mostly northern, while the Celleporida are found in both north and south temperate seas. But the great mass of the families are either universally distributed or widely scattered over the globe. They range to high northern latitudes, having been found abundantly by the Swedish expedition on the shores of Nova Zembla in 70° N. lat. They inhabit the profound depths of the ocean, having been dredged from near 2000 fathoms in the North Atlantic, 2500 fathoms in the Pacific, and 2650 fathoms in the Southern Ocean during the voyage of the "Challenger." (Busk's Brit. Mus. Catalogue of Marine Polyzoa; "Challenger' Reports," Proc. Roy. Society, vol. xxiv. pp. 466, 468, 572, 635.) Echinodermata.-The best-known groups-the starfishes and sea-urchins-occur abundantly as fossils, but their existing distribution does not offer many features of special interest. The Asteroidea, or star-fishes, are most abundant in the Indian and Pacific oceans, while the Ophiuroidea (brittle stars) are better represented in the European and African seas. A few genera are exclusively American, but on the whole star-fishes are far less abundant in the western than in the eastern hemisphere. Although most abundant in shallow seas, they also inhabit the floors of the deepest oceans, some having been obtained by the " Challenger expedition from a depth of 2700 fathoms in the Pacific. They abound even in the Arctic seas, "hundreds of seastars" having been obtained by a single haul of the swab at 76° N. lat. in Novaya Zembla by the Swedish exploring ship "Proven" in 1875. The Echinoidea (seaurchins) are also very abundant in Eastern seas, while they are comparatively scarce in America. Although much larger and more varied in the tropics, they are tolerably abundant in temperate and cold seas; and they probably reach the greatest depths in the ocean, since some have been obtained by the "Challenger" from a depth of nearly 3000 fathoms in the North Pacific. (Nature, vol. xii. p. 556; Van der Hoeven, Handbook of Zoology.) no less than 115 peculiar genera, and only 19 in common with the Africo-European region. About 40 genera are said to be found in all three regions. The distribution of Crustacea in relation to temperature also presents some peculiar features. The species are almost equally divided between the tropical and the extratropical regions. The highest form of Crustacea-the Brachyura-are most abundant in the tropics, while the less developed Amphipoda and Isopoda are more numerous in temperate and frigid zones. This may, however, in part depend on these groups having been less assiduously collected in the tropics. More interesting, and less open to doubt, is the fact that among the four chief types of Crustacea-Brachyura, Macroura, Isopoda, and Amphipoda -the most highly developed species are extra-tropical. The largest species of the Macroura are found in temperate seas, and though the largest Brachyura are tropical, yet the Maioids the highest group of Brachyura and of all Crustaceans-reach their largest dimensions in the temperate zone. Mr Spence Bate adduces the curious fact that in the cosmopolite sub-family Lysianassina, the largest species are found in Arctic and Antarctic latitudes, while a species from the Straits of Magellan so closely resembles one from Spitzbergen that they may even be identical; and in the family Caprellide the same species often occurs in both the northern and southern hemispheres. Mr Dana lays great stress on similar cases of wide and discontinuous distribution, which (he considers) necessitate the adoption of the theory of special-creations. Thus, two species (Kraussia rugulosa and Galene natalensis) are found at the Hawaian islands and Natal, but in no intermediate localities. Other identical species occur in the Japan seas and Natal. The same species (Plagusia tomentosa) occurs in South Africa, New Zealand, and Valparaiso; and another (Cancer Edwardsii) at New Zealand and Valparaiso. The same species and several identical genera (Latreillia, Ephyra, Sicyonia) are found in the Mediterranean Sea and Japan, but in no intermediate districts. Closely allied species (of the genera Amphiroidea and Ozius) are found in Australia and Chili; but perhaps the most singular fact is the occurrence of closely allied or perhaps identical species of Palamon in New Zealand and the British Seas, and also of certain British or American genera (as Portunus and Cancer) in New Zealand. Many of these cases, and more especially the last, undoubtedly offer great difficulties on the theory of transmission and specific modification. There are, however, some considerations which afford hints for a possible solution of the difficulty. We now know many cases in which the distribution of an animal or a group of The marine regions which best represent the distribution animals has been rendered discontinuous by its recent exof these animals are three in number, termed by Mr Dana tinction in intermediate localities. The tapirs, for example, the Occidental, the Africo-European, and the Oriental. exist only in tropical America and the Malay islands, and it The first comprises both coasts of the American continent; might well be argued that no passage from one of these the second, the eastern shores of the Atlantic both African localities to the other is conceivable for such an animal. and European; and the third comprehends the vast area But we now know that the South American tapir lived in from the east coast of Africa to the Central Pacific. Each North America down to post-Pliocene times, that in Europe of these is of course subdivided into climatal and local there were tapirs in the later Pliocene period, while in the provinces, but the primary divisions alone are those which Pliocene or Miocene periods allied species inhabited North we have now to consider. The facts adduced in support India and some parts of China. The present remotely of this scheme of distribution are very interesting. No isolated forms are therefore seen to be the remnants of a less than 47 genera are exclusively American, and 15 are genus which once ranged over almost the whole northern common to both the east and west coasts; but as 26 genera | hemisphere. Perhaps more to the point is the case of the are said to be confined to the west coast, and 6 to the cast, genus Panopaa, adduced by Mr Woodward in his Manual it will be seen that these two provinces are really very dis- of the Mollusca. There are only 11 living species, which tinct, even if they do not form primary regions. The occur widely scattered in the northern seas, the Cape of Africo-European region has 19 peculiar genera, and only 8 Good Hope, Australia, New Zealand, and Patagonia. But in common with the American region; so that the eastern of this same genus nearly 150 fossil species are known, disand western shores of the Atlantic are decidedly more distributed over many intermediate localities, so that the tinct than the eastern and western coasts of America. The existing species are seen to be but relics of an ancient form extensive Oriental region is by far the richest, containing of life lingering at various points on the outskirts of the Crustacea. The distribution of the higher Crustacea has been discussed in detail by Mr James Dana in the Zoology of the United States Exploring Expedition; and, considering that most of the species are shore-dwellers, the facts are very interesting and often quite unexpected. We will, therefore, give an abstract of the conclusions of this writer. Cirrhipedia. The barnacles are a tolerably extensive group of anomalous Crustacea, whose distribution differs somewhat from that of the more typical portion of the class. The genera are almost all widely or universally distributed, from 74° 18' N. lat. to Cape Horn, and some of the species have an equally wide range. No genus having more than a single species is confined to the torrid zones, and only two genera are limited to the southern hemisphere. Although the temperate zones have a smaller area than the torrid, they possess rather more species of Cirrhipeds, which Mr Darwin imputes to the fact of these zones being two, while the torrid is but one. As in some groups of the higher Crustacea, large species are most abundant in the temperate zones. Owing to the wide determined by the distribution of species. These, according to Mr Darwin, are as follows:-1. The North Atlantic, comprising North America and Europe down to N. lat 30°; 2. The West American, from Behring Straits to Tierradel-Fuego; 3. The Malayan, from India to New Guinea; 4. The Australian, comprising Australia and New Zealand. The Malayan and Australian regions are the richest in Cirrhipeds. During the voyage of the "Challenger" these animals were found to inhabit the deep seas, the most remarkable being a gigantic Scalpellum from a depth of 2850 fathoms in the North Atlantic, while other forms occurred at almost the same depth in the Pacific. (Darwin's Monograph of Cirrhipedia," Ray Society, 1854.) vast area it once occupied. Such cases as these occur in | Crustacea of the 'Challenger,'" Proc. of the Royal Society, all classes of animals where our knowledge of the extinct vol. xxiv. p. 585.) fauna is sufficiently extensive, and we are therefore justified in believing that a large proportion of the existing instances of anomalous and discontinuous distribution are to be explained in a similar way. In the case of the Crustacea we must also take into account our comparative ignorance of many parts of the globe, and especially our ignorance of the powers of dispersal of the ova, and of the young animals during their earlier larval condition. This dispersal may systematically occur to a far greater extent than we are yet aware of; though only in rare and exceptional instances may a species succeed in maintaining itself beyond the normal limits of its race. The certainty we are now acquiring of the long duration and wide-spread influence of the glacial period must also materially affect such questions as these; for although the equatorial low-range of the genera the Cirrhipedal regions can only be lands may never have suffered from its influence, it is highly probable that during the period of greatest cold the temperature of the entire ocean may have been lowered, while in certain directions cold currents may have afforded a passage for temperate forms of marine animals from the northern to the southern hemisphere. While admitting, therefore, that the distribution of Crustacea presents to us some problems of extreme difficulty, we must deny that they are such as to justify us in resorting to a solution such as special creation," which is negatived by the evidence afforded by almost every other class of animals. The reports of the "Challenger" expedition already published afford valuable information on the distribution of Crustacea in the oceanic depths. The higher forms (Decapoda) have been found living at a depth of 1875 fathoms in the North Pacific, 2600 fathoms under the equator, and 2385 fathoms in the South Pacific. In the North Atlantic, at a depth of 1900 fathoms, was found a cray-fish allied to the Astacido, but deprived of even the rudiments of eyes, while others equally blind (from both the Atlantic and Pacific) are believed to have their nearest allies among the extinct Eryonida of the Jurassic period. The higher Crustacea, which are most abundant at great depths, and which have afforded the greatest variety of new and interesting forms, belong to the Schizopoda. They have been found at depths of more than 2000 fathoms in the Pacific, and down to 2550 fathoms in the Atlantic Ocean. Some of them are blind, but a more remarkable fact is, that many of them are brightly coloured, though living in absolute and perpetual darkness. Among the Edriopthalmata (sessile-eyed Crustacea) examples of the remarkable blind family Munopsidae have been found at a depth of 2175 fathoms in the Atlantic, and at nearly 2000 fathoms in the Southern Ocean. Other forms usually found in shallow water (Serolis) also occurred at great depths-more than 2000 fathoms in the Pacific; and one of these, obtained near the southern ice-barrier at a depth of over 1900 fathoms, was of "a fine blue colour with a red spot over the middle of the body." Entomostraca also occur at great deptus, the most remarkable being a gigantic Ostracod found at 1600 fathoms in the Southern Ocean. At 1375 fathoms, near the Crozets, a Pycnogonoid (sea-spider) was obtained, measuring 2 feet across the legs. But besides these bottom-dwellers, the trawl nets at different depths showed that the ocean is inhabited by peculiar tribes of free-swimmers-principally Copepoda, Amphipoda, and Cypridinas, often of a bright orange colour. These occurred in all parts of the Pacific to a depth of 2000 fathoms, but they were never found in the surface nets. (United States Exploring Expedition, vols xiii. and xiv.; Spence Bate on Geographical Distribution," in Spence Bate and Westwood's British Sessile-Eyed Crustacea; Dr Rudolf von Willemöes-Sulim's "Report on the 66 Mollusca.-The marine Mollusca, from their great abundance in all seas, the ardour with which they have been collected and studied, and the frequency of their occurrence as fossils, offer an extensive field for the study of distribution. But many causes have combined to render the results yet arrived at unsatisfactory. Their classification has been for some time undergoing a progressive change, owing to the greater attention paid to the organization and development of the animals, but there is still much uncertainty as to the limits of genera and sub-genera. Owing to their being in many cases articles of commerce, either on account of their uses or their beauty, the place where they were originally obtained has often been confused with the place from which they were exported. Their numbers, too, have so rapidly increased that few persons have been found to devote themselves to the great labour of geographical tabulation. And, lastly, the genera are so often of great extent and world-wide distribution that the range of species alone has generally been attended to. The late Dr Woodward established a series of eighteen marine provinces, founded professedly on the fact of onehalf of the species being peculiar. The distribution of the genera is only casually mentioned, and it is almost certain that a large number of these provinces have no claim to rank as primary regions as regards the distribution of the Molluscan fauna. Dr Woodward himself states that his Arctic province is comparatively small and exceptional, while the three southern faunas of America, Africa, and Australia differ extremely. All the warmer provinces may, he says, be naturally grouped into three great divisionsthe Atlantic, the Indo-Pacific, and the West American; and these are perhaps the only true Molluscan regions. The Indo-Pacific extends from the Red Sea and east coast of Africa to the easternmost Pacific islands, and exactly corresponds to Mr Dana's Oriental region for Crustacea. About 100 species are said to range over nearly the whole of this vast area. The Atlantic region unites the fauna of the east coast of America with that of West Africa and South Europe, but it also has considerable affinity for that of West America, since about 60 genera are common to | pp. 536, 578; Letters of Sir Wyville Thomson, in both. Several important genera appear to be restricted to | Nature, vols. 7–10.) the north temperate zone, which should perhaps form a distinct region. About 30 important genera are confined to the Indo-Pacific region; and nearly 20 are peculiarly tropical. The Atlantic coasts have few peculiar genera of importance, and the west coast of America hardly any, its difference from the Atlantic fauna on the one side and the Pacific on the other being chiefly specific. There is said to be not a single species common to he east and west coasts of tropical South America; while the corresponding coasts of North America have more than 50 species in common, and many others so closely representative as to be almost equivalent to identical species. The shells of the Mediterranean were once supposed to be very peculiar, but recent dredgings have proved that most of them exist also in the Atlantic, and it is now doubted if any are really confined to that sea. A small number (about 70 or 80 species) are identical with Red Sea shells. The marine-shells of Australia and New Zealand are exceedingly unlike those of Britain,-exactly the reverse of what obtains among the Crustacea. The influence of temperature on the distribution of Mollusca is very marked, the warmer regions presenting a greater variety of forms, with a greater proportion of large and finely-coloured species. Yet in some cases the largest species are extra-tropical, a striking example being found among the volutes, which abound in tropical seas, yet attain their largest size in New Zealand. In temperate and even in Arctic seas Mollusca are perhaps as abundant individually as in the tropics, but the number of species and genera is far less, and they are generally dwarfed in size, and of obscure colours. Till a comparatively recent period very few shells had been obtained at a greater depth than 200 fathoms. These were mostly of small size and obscure colours, belonging to groups of wide range and great geological antiquity. Dentalium, Cryptodon, Leda, and Arca were the most important, and it was generally believed that the zero of Molluscan, if not of all but the very lowest forms of life, | would be found at a depth of 300 or 400 fathoms. The recent development of deep-sea dredging has, however, completely changed our ideas on this subject, and the Mollusca as well as most other groups of Invertebrata are found to be capable of existing in the profoundest depths of the ocean. Off the coast of Norway Professor Sars has obtained Mollusca from a depth of 450 fathoms; and near Florida, Agassiz found them at 500 fathoms. During the cruise of the "Porcupine" Professor Wyville Thomson obtained species of Pleurotoma and Dentalium from the enormous depth of 2500 fathoms in the Bay of Biscay. During the recent voyage of the "Challenger" many other groups have been discovered in the deepest seas. In the North Atlantic, 500 miles west of Teneriffe, three small living Mollusca belonging to the genera Arca, Limopsis, and Leda were dredged from a depth of 2740 fathoms; while in the Central Pacific, from a depth of 2425 fathoms, species of Arca, Neæra, Pleuronectia, Trochus, Fusus, Dentalium, and some others have been obtained. All are small obscurely-coloured forms, resembling Arctic rather than tropical shells, due no doubt to the fact that in these profound depths the water is permanently at a temperature very little differing from that of melting ice. Equally interesting is the fact ascertained by the naturalists of the Challenger," that the waters of the ocean down to the enormous depth of 1500 fathoms abound with true pelagic Mollusca belonging to the orders Pteropoda, Heteropoda, and Gasteropoda, while below this limit they appear to be absent. (Woodward's Manual of the Mollusca; Challenger' Reports," Proc. Royal Society, vol xxiv. Fishes.-The distribution of marine fishes appeals to agree generally with that of the Mollusca and Crustacea, their greater powers of locomotion, leading to a wider dispersal, being to some extent compensated by the more recent origin of most of the species, genera, and families. There are about 80 families of marine fishes, and no less than 50 of these are almost universally distributed. Several other families range over all tropical seas. About 5 families are found only in the Arctic and temperate seas of both hemispheres, while two (Discoboli and Accipenserida) are found in the north temperate seas only. The best marked region is undoubtedly (as in the Mollusca and Crustacea) that which extends from the Red Sea and east coast of Africa to the Sandwich Islands and Australia. About ten families are confined to this region (which may be termed the Oriental or Indo-Pacific marine region); many genera of other families equally characterize it, while there are even a number of species which range over the greater part of its vast area. On the other hand, no family of importance seems to be confined to the Atlantic, or to the coasts of Eastern or Western America, the differences of these provinces, as of the European and American shores of the Atlantic, being confined to generic and still more largely to specific forms. Many species of fish have enormous ranges, extending from the North Atlantic to Australia, from the Red Sea to the Sandwich Islands, and from New Zealand to South America. Some species range over almost the whole Atlantic Ocean, and a considerable proportion of those inhabiting the Atlantic and Pacific coasts of Central America have been found by Dr Günther to be identical. It has long been known that a considerable number of fishes inbabit very deep water, never coming to the surface when alive; but the researches of the "Challenger" expedition have added greatly to our knowledge of these curious forms. A large number of genera and species, many of them new, and belonging to ten distinct families, have been obtained in the nets and trawls from a depth of 200 to 2400 fathoms in all the great oceans. These often come up greatly inflated by the expansion of the internal gases; some were transparent, several were blind, and some had curious phosphorescent organs on the head. These deepsea forms generally have a wide range. The greater num ber of the new and remarkable forms obtained during the voyage of the "Challenger" belong to the Scopelidæ, a family known to inhabit the deep waters of all the warmer The size attained by marine fishes appears to have no relation to latitude or temperature. (Günther's British Museum Catalogue of Fishes; Mr J. Murray's " Preliminary Report on Vertebrates collected by the 'Challenger,'" Pro. Roy. Soc., vol. xxiv. p. 537.) seas. Marine Turtles. These reptiles, forming the family Cheloniida, are too few in number and too widely distri buted to afford any indications as to oceanic regions. Cetacea. The whales and dolphins form the only group ot truly oceanic Mammalia. They are very widely distri buted, but their classification is too unsettled, and their history too imperfectly known, to throw much light on the general question of oceanic distribution. Two of the families-Balanida and Balanopterida-seem to be confined to the cold and temperate seas of both hemispheres. The Catodontidae (comprising the sperm whales), on the other hand, are more especially tropical and sub-tropical. The Hyperoodontidæ, or beaked-whales, are widely distributed in northern, southern, and tropical seas; while tho largest family-the Delphinida―are universally distributed. The largest whales inhabit the cold northern and southern seas. (Dr J. E. Gray's British Museum Catalogue of |
