18,250,000 annually. March to August is the period of greatest catch.1

The river cray-fish, Astacus fluviatilis (fig. 25), also common to the rivers of Europe, is largely caught, and when fresh boiled is not to be despised. It is largely imported into London, and is used by the chefs at the West End to garnish dishes. The writer with a friend caught as many as 900 cray-fish in a single evening from 8 till 12 (with a series of simple scale-like nets baited with liver), along the bank of the Thames and Severn Canal, Gloucestershire. The Murray river cray-fish from Australia (Potamobius serratus) is as large as a fine sea-lobster, and has its segments ornamented with spines, reminding one of the spiny lobster (Enoploclytia sussexiensis) from the chalk of Sussex and Kent.3

More than fifty genera of fossil Macroura have been met with and described; the earliest known is the Anthra palamon Grossartii from the Lower Carboniferous series near Glasgow. Similar forms have been obtained from the Coal-measures in England; from Illinois, U.S.; from Bohemia, &c.

I. PODOPHTHALMIA: (2.) STOMAPODA.-All the members embraced within the three divisions of the preceding order (Decapoda) were cryptobranchiate, in this order they are nudibranchiate, i.e., the gills are composed of plates or simple filaments attached to the feet, whilst the carapace, so largely developed in the order Decapoda, is here both shorter and narrower, and the body less compact. Taking Squilla (fig. 71) as an example, the segments are much less coalesced than in the lobster. Those bearing the eyes and the antennules are readily separable from the front of the head, and are not covered by the carapace, which only conceals eight segments, whereas in the lobster it covers fourteen, and in the crab twenty-one. The gills are borne by the abdominal swimming feet, free and uncovered. The first pair of thoracic limbs are developed into a pair of large and formidable claws, the terminal joint of Fig. 71.--Squilla mantis, Rondel.; which bears a terranean. row of long, sharp, and recurved teeth; these double back upon the edge of the penultimate joint which has a groove to receive them, like a pocket-comb.

south coast of England and Medi

In Mysis, "the opossum shrimp," another member of this order, the two posterior pairs of feet only are branchiferous; all the feet are biramous and flagellate; in the female the hinder feet are modified into broad plates which, uniting beneath the body, form a pouch or marsupium in

1 Lobsters are sent alive to the London market, packed in damp sea. weed, moss, or heather, from Stornoway in the Island of Lewis, from Ireland, Scotland, the Orkneys, the south coast, and Channel Islands, and from Norway. Fishermen and salesmen are said to know the south coast, Cornish, Scotch, Irish, or Norwegian lobsters at sight, just as cattle salesmen know a Hereford" or 66 "Devon," a Scotch or "Irish "beast. The largest common lobsters weigh from 8 to 12 lb. But the great lobster of the American coast (largely imported in tins into Europe) weighs more than twice as much.

Dixon's Geology of Sussex, tab. 38, figs. 6, 7.

"

3 For the numerous species of Palamonida belonging to this division, we must refer the reader to Bell's British Stalk-eyed Crustacea, to Dana's magnificent volumes and atlas on the Crustacea found during the United States exploring expedition, and to De Haan's Fauna Japonica, and Milne-Edwards's Hist, Nat, des Crustacées.

which the eggs are protected and the young pass through their infancy.*

These opossum-shrimps, which are pelagic in their habits, are frequently met with in countless myriads towards the surface of the Greenland Sea, and, though small, they form the chief part of the food of the common whale (Balana mysticetus).5

Some forms of Erichthys are included in this division; these, like Mysis, are also pelagic, and occur abundantly on the surface of the Indian and Atlantic Oceans, where, together with the larvae of Cirripedes and many other oceanic cosmopolites, they may be taken with the towing net in abundance.

Numerous specimens of true Squilla (Sculda pennata, Münst) and of a Mysis-like Crustacean have been found fossil in the Solenhofen limestone, of Oolitic age, in Bavaria. With the Stomapoda are also placed a group of very anomalous and larval-looking Crustacea (the Diastylide) originally noticed in 1843 by Mr Harry Goodsir, who obtained them from the Firth of Forth. They closely resemble Copepoda in aspect, and might readily be confounded with the larval stages of some Decapod. They have, however, been found with their eggs borne by the female in an incubatory pouch beneath the thorax, as in Mysis.

The branchiæ are situated on each side of the thorax immediately above the insertion of the legs, and approach in their comb-like appearance to those of the higher Crustacea.

Three genera have been established for these singular forms, namely, Cuma, Alauna, Bodotria (see fig. 36).

II. EDRIOPHTHALMIA: (3.) ISOPODA.-From the stalk-eyed Podophthalmia we pass now to the sessile-eyed Edriophthalmia, in which the eyes with one exception are fixed immovably on the surface of the head. As in the higher forms, the eyes are compound, consisting in the young of some ten or twelve lenses only, but in the adult of as many as sixty to eighty. In nearly all, the body is distinctly divisible into three parts-the head usually very small, the seven thoracic segments well and evenly developed, the abdominal somites more or less coalesced. The general conformity in size and function of the thoracic somites and their seven pairs of legs characterizes the majority of the Isopoda. These legs are nearly uniform, and are fitted either for walking or for swimming, or as powerful hooklike organs to enable them to adhere to the fishes on which they are parasitic. The branchiæ in this order are transferred from the thoracic legs to the abdominal appendages, which are converted into special organs of respiration.

One group of Isopods, the Oniscidae (forming Spence Bate's and Westwood's family Erospirantia), familiar in our gardens under the names of "woodlouse," "sow-bug," and "armadillo" (fig. 22), are all air-breathers, incapable of existing in water, but breathing air which, however, it is necessary must be saturated with moisture. Several of the species which inhabit caves are destitute of eyes (eg., Titanethes albus, Schrodte). The "great sea-slater" (Ligia oceanica) is common on all our coasts, running with agility and feigning death when attacked. The genus Armadillo, found commonly in our gardens and woods, and so called from the perfect way in which the segments roll together, forcibly reminds one of "the great Barr Trilobite " (Illanus Barriensis), from the Silurian of Staffordshire (7 in fig. 73).

A very interesting little Isopod (presented to the British Museum by Dr Milligan of Tasmania), from Flinders Island, Bass's Straits, and named in MS. by

4 An allied species to Mysis, Thysanopoda (obtained in myriads by Couch on the Cornish coast from the stomachs of mackerel), carries its eggs, as does Cyclops quadricornis, in two bag-like ovaries depending from the posterior thoracic somite (Bell's Brit. Stalk-eyed Crust.) 5 Otho Fabricius, Fauna Groenlandica, p. 245.

on one side. A fossil Bopyrus is observed lying in the branchial cavity of a crab (Palaeocorystes) from the Gault and Greensand. We have already referred to these and other parasitic forms in the earlier part of this article.

Isopoda are met with as far back as the Old Red Sandstone, where remains of a gigantic species allied to Arcturus have been discovered; others occur in the Carboniferous and Oolitic periods. The Purbeck beds of Swanage, Dorset, also yield abundance of a freshwater form, the Archæoniscus Brodiei; species of Oniscus and Sphæroma are found fossil in the Cretaceous, the Eocene, and the Miocene of Europe. II. EDRIOPHTHALMIA: (4.) TRILOBITA.-So long ago as 1821 Audouin placed the Trilobites with the Isopoda, whilst Macleay assigned them a distinct order between the Isopoda and the Phyllopoda. Later researches by Milne-Edwards

FIG. 72.-Ceratocephalus Grayanus; Flinders island, Bass's Straits. A, the dorsal aspect. B, front view of the head showing the curvature of the three spines. C, side view. D, ventral aspect: g, the glabellal spine; 1,4, the two lateral or genal spines of the head; e, the eye; a,' the antennule; a", the antennæ; the legs are seen folded up beneath the body. E, the mouth enlarged, showing ep, the epistoma or upper lip plate, m', the mandibles, m", the pectinated maxilla, a, the antenna; the epistoma is set in the base of the glabellal spine g.. concealment beneath the body-segments, are very suggestive. This Isopod is near to the Sphæromide, but will form a distinct family, as the antennæ are inserted beneath and within the margin of the head-shield; apparently it does not roll itself into a ball.

The Sphæromide are very littoral in their habits; they

zones, but are not found in Polar regions. They are vegetable feeders, and some (like Limnoria) are guilty of destroying timber. When molested or alarmed they roll themselves up into a ball. The Sphæromide present many points of analogy, if not of affinity, with the extinct Trilobites. In this order we find the Limnoria terebrans (or the gribble," as it is called by the fishermen). It is one of the most destructive creatures, attacking all woodwork below tidemarks; the only wood which it cannot destroy is teak. Although its ravages had gone on for ages, it was only made known to the scientific world and described by Dr Leach in 1811.

In the aberrant genus Tanais (fig. 38) the first pair of thoracic legs are converted into chela, and the head-shield is covered by a carapace, abundantly traversed by currents of blood, beneath which a stream of water passes, maintained as in the zoëæ and adult Decapoda by a flabelliform appendage of the second pair of maxille, which is wanting in all other Edriophthalmia. The abdominal feet, which in other Isopoda act as respiratory organs, are simple natatory feet in Tanais. These characters, together with the pedunculated eyes and the great chelate hands, give to Tanais a very decapod-like aspect (see fig. 38).

The Idoteidae contain representatives of some of the largest known Isopoda, some of which are above 4 inches in length.

The Egide and Cymothoida have all the feet furnished with a robust finger, sharp at the tip, for seizing and holding on to fishes upon which they are parasitic. Another family, the Bopyrida (fig. 39) are parasitic chiefly on members of their own class, frequently occupying the branchial chamber of the common prawn, and distorting the carapace

1 One species, Eurydice pulchra, common in the Dee, Cheshire, actually attacks bathers. "If you remain a moment still in the water dozens will fasten on you and nip most unpleasantly. I have had to jump into the water again after coming out from bathing, and splash violently to get rid of the hosts that had stuck to me while clinging to the side of the boat preparatory to getting in. They con tinue to bite after you are out of the water."-Extract of letter from Mr Walker to Mr C. Spence Bate.

Scouleri, M.C.; Carbonifs. L, Ireland. 3, Beyrichia complicata, Salter; Lr. Silurian, Wales. 4, Dithyrocaris Scouleri. M'Coy; Carbonifs. L. Ireland. 5, Pterygotus anglicus, Ag.; Old Red, Forfarshire. 6, Prestwichia rotundata, II. Woodw. Carbonifs., Coalbrookdale. 7, Illanus Davisii, Salter; L. Silurian, Bala. 8, Phacops caudatus, Brunn.; U. Silurian, Dudley. 9, Calymens Blumenbachii, Br.; U. Silurian, Dudley. 10, Trinucleus ornatus, Sternb.; L. Silurian, Britain. 11, Agnostus trinodus, Salter: Lr. Silurian, Britain.

and others have caused the Trilobita to be referred to the Entomostraca, on account of the very variable number of body-rings observed in the several genera (from six to twenty-six) evidencing a much lower type of structure than the Isopoda, in which the thorax is composed of seven free and movable segments with a head-shield and anchylosed caudal somites. Moreover, until the discovery of presumed ambulatory appendages in an Asaphus from the Trenton Limestone in 1870,3 the only appendage previously observed was the hypostome or lip-plate. There seems, however, no good reason to urge against the conclusion that the Trilobita were an earlier and more generalized type of Crustacea, from which the later and more specialized Isopoda have arisen,-a view which the writer is glad to say he shares with the distinguished carcinologists, Professor Dana in America, and Mr C. Spence Bate in England, although at present more evidence is needed as to the nature of the locomotory appendages in this extinct group. If we range the characters of Trilobita and Isopoda side by

2 Mr James Carter, F. G.S., lately showed the writer a Palaocorystes from the Cambridge Greensand, having a Bopyrus lodged in each of its branchial chambers.

3 Billings, Quart. Journ. Geol. Soc., vol. xxvi. p. 479.

4 Professor Dana writes, "The Trilobita probably belong with this

second type" (the Edriophthalmia, or Tetradecapoda, as Dana names them) "rather than with the Entomostraca. Yet they show an aberrant character in two important points. First, the segments of the body are multiplied much beyond the normal number, as in the Phyllopoda among the Entomostraca; and Agassiz has remarked upon this as evidence of that larval analogy which characterizes in many cases the earlier forms of animal life. In the second place, the size of the body far transcends the ordinary Isopodan limit. This might be considered a mark of superiority; but it is more probably the reverse. It is an enlargement beyond the normal and most effective size, due to the same principle of vegetative growth which accords with the (occasional) inordinate multiplication of the segments in the body" (American Journ, Science, July, 1856, vol. xxii. p. 11),

1

4. Thoracic segments variable in 4. number, from even to 26,

free and movable, animal
sometimes rolling in a ball.

5. Abdominal somites coalesced, 5.
forming a broad caudal shield
(bearing the branchia be-
neath?).

6. Lip-plate, well-developed.

Appendages partly oral, partly ambulatory, arranged in pairs.

Thoracic segments usually seven, free and movable, animal sometimes rolling in a ball.

Abdominal somites coalesced, forming a broad caudal shield, bearing the bran chiæ beneath. 6. Lip-plate, small.

1. Young individual, destitute of thoracic segments, composed of head-shield and um only. 2. An

py

er of the same stage, in which the genal or cheek spines are developed. 3. Individual with one thoracic segment developed, but without the genal spines.

4. Another of the same stage, with the genal spines.

5. Individual with two thoracic segments, and with the genal spines present. 4. Individual with three thoracic segments, and possessing the genal spines. 7. Individual with five thoracic segments, but without genal spines. absolutely adhered to without any variations; on the contrary, we constantly meet with individuals in which more or fewer segments are welded together, so as to conceal the normal number of seven thoracic somites between the head and the abdomen. Such being the case, we cannot be surprised to find considerable variation in a group like the Trilobita, which, if they really are the remote ancestors of the recent Isopoda, must, according to the views suggested above, be the prototypes of the larva rather than of the adult stage of the living Isopoda.2

In his researches among the Trilobites of Bohemia M. Barrande has discovered forms which, there is every reason to believe, exhibit (as he has so admirably shown in his

1 H. Woodward, Report on Structure and Classification of Fossil Crustacea, Brit. Assoc. Edinburgh, 1871.

2 The larvae of Bopyrus, Cryptothiria, and Asellus, and the adult Egida, Idoteida, Sphæromida, and Oniscidae offer many points of analogy with the extinct Trilobita (see the History of the British Sessile-eyed Crustacea by C. Spence Bate, F.R.S. and J. O. Westwood, M.A., in 2 vols. 1863-68, 8vo.)

the earliest form on quitting the egg to the adult. We give seven of the earliest stages of Trinucleus ornatus and seven of Sao hirsuta, copied from M. Barrande's monograph.

FIG. 75.-Sao hirsuta, Barrande (copied from pl. 7 of Barrande's work above cited). Barrande figures twenty stages of this trilobite, of which seven are reproduced here.

1. First stage. A young individual in which the limit of the head-shield is not indicated as separating it from the pygidium.

2. Second stage. Young individual with the head-shield separated, and having indications of three soldered segments to the pygidium.

3. Third stage, in which the genal angles of the head and the spiny border of the pygidium are well seen, and four or five soldered segments indicated.

4. Fourth stage, in which two free thoracic segments are developed behind the head, and two or three soldered segments represent the pygidium.

5. Fifth stage, in which the thorax is longer than the head, and is composed of three movable segments and three soldered segments in the pygidium.

6. Sixth stage, in which four free segments succeed the head, and three or four soldered segments form the pygidium.

7. Tenth stage, in which eight free segments succeed the head, and three soldered segments form the pygidium.

In the twentieth stage figured by Barrande the adult has seventeen free thoracico-abdominal segments and two soldered ones (the pygidium).

One most striking feature in the Trilobita is the reinarkable development of their compound eyes (fig. 11), a subject ably discussed and illustrated long ago by Dr Buckland in his Bridgewater Treatise (1836).

Perhaps the eye of the Trilobite may be best compared with that of Limulus, but there are forms like Eglina in which the eyes are enormously developed, occupying nearly the entire head-shield with their facetted surfaces.

We have an analogous development of the organs vision amongst some of the pelagic Amphipoda, the Hyperiidae, and in a very singular form brought home by 1873). The "facial suture" in the head-shield of the Trilothe "Challenger," the Thaumops pellucida (Phil. Trans. bita, which separates the lateral genal portion from the glabella, was for a long time considered as peculiar to Trilobites and Limuli, but C. Spence Bate has ably shown that it homologizes with the suture which traverses the inferior surface in the carapace of the Brachyurous Decapod and the cervical suture in the Macrouran type (Reports Brit. Assoc., Bristol, 1875, p. 46.)

The Trilobita are the chief representatives of the Crustacean class in Cambrian times.3 More than 500 species have been described; out of these 350, representing 42 genera, have been recorded from the Lower Paleozoic rocks of Bohemia alone by Barrande.

About 51 genera and 304 species are British in Cambrian and Silurian rocks; ten are Devonian, and four Carboniferous. A gigantic Paradoxides, nearly two feet in length, occurs in the Middle Cambrian, and large forms of Asaphus, Homalonotus, Lichas, &c., are met in the Bala group. Phacops, Sphærexochus, Encrinurus, Calymene, Illanus, and Acidaspis are among the Upper Silurian forms, some, like Acidaspis, being extravagantly orna mented with spines and tubercles. The Devonian has

3 Agrostus, the earliest genus met with, reminds one of the larval forms of Sao and Trinucleus.

The large accession in late years to the fauna of these Cambrian rocks has resulted from the labours of Mr Henry Hicks, F.G.S.

fewer and less varied forms of Trilobites. Those in the Carboniferous belong nearly all to two genera (Phillipsia and Griffithides), both small, neat, and simple forms. None are met with in rocks of later date.

II. EDRIOPHTHALMIA : (5.) AMPHIPODA. This order, as Spence Bate has well observed, constitutes a group among the Edriophthalmia, parallel with the Macroura among the Podophthalmia, whilst the Isopoda may represent the broad and flattened Brachyura, the Caprella offering a kind of parallelism with Squilla and its allies. As in the Isopoda, the head is small and carries only the organs of sense and nutrition; the sessile eyes1 are generally small, yet in a few instances they are extremely large (e.g., Lestrigonus and Thaumops), covering the entire sides of the head. The seven thoracic segments, constituting the middle-body, are well developed and nearly equal in size; all the segments are compressed laterally as in the Palaemonidæ.

The two anterior pairs of the seven thoracic legs (see Th. 8, 9 in fig. 1), which are jaw-feet in the Podophthalmia, are here developed into arm-like legs, having an enlarged penultimate joint or hand, against which the seventh and terminal joint doubles back, like a finger against the palm, and so forms a prehensile organ similar in form to the claws in the Crangonidae. The best-formed claws are seen in Orchestia Darwinii (fig. 45), and in Melita exilii (fig. 76).

FIG. 76. Melita erilii, n. sp., male, enlarged five times. The large branchial lamellæ are seen projecting between the legs. (Fritz Müller.)

The ova are nourished within a pouch formed by a series of foliaceous plates attached to the four anterior pairs of legs; except in the Hyperiidae, which are parasitic on Medusa, as already mentioned. The males in the Amphipoda closely resemble the females (save in those forms in which the hands are enlarged in the male), but contrary to the general rule the females are much smaller than the males.

This division, like the preceding one, has its terrestrial representatives, Talitrus and Orchestia, the "sandhoppers," living out of the sea, but choosing moist places. Orchestia with us loves to live within reach of the sea spray, but some species in the southern hemisphere (O. tahitiensis, telluris, and sylvicola) live many miles inland, some under plants at an elevation of more than a thousand

1 The outer integument of the eyes is never divided into facets, except in the Hyperiida. In many of the Phoxides the eyes appear to be wanting; but this is probably caused by the absence of any colouring pigment. In Niphargus the eyes are obsolete or rudimentary. In Ampelisca they appear like four simple organs resembling the ocelli of

true insects (Spence Bate and Westwood, Brit. Sess. Crust. vol. i. p. 4).

It is in the summer months that they occur in such vast myriads npon our sandy shores. At Whitsand Bay Mr Twain saw "not millions, but cartloads," of one species (Talitrus locusta) lying piled together along the margin of the sea. They devour offal of every description, including dead carcasses of animals, which they rapidly assimilate and remove. In their turn they afford a repast to the ring plover, the common wood-pigeon, and numerous shore-birds which rapidly devour them, as well as some coleopterous insects (the Cillenum laterals and Broscus cephalotes (Bate and Westwood).

feet above the sea. But by far the largest section are natatorial in their habits, being most active and untiring swimmers. One form, Gammarus pulex (fig. 77), is most common in our freshwaters, two other genera, both blind, Niphargus, with three species, FIG. 77-Gammarus, sp., fresh water. and Crangonyx, with one species, are found in wells in England, and from their structure there is every reason to conclude they are as truly indigenous to these underground water-courses in the Chalk, Oolite, or Carboniferous Limestone, as are the numerous species of blind Crustacea met with in the waters flowing through the Mammoth Cave, Kentucky.

A curious subdivision of Amphipods is formed by the Podocerides (Amphithoë and Podocerus), all the species of which invariably construct nests in which they take shelter and nourish their young. These abodes are built of wood or stones, mud, clay, &c., united together by a cement excreted by the animals themselves. Some closely resemble miniature birds'-nests, others are in the form of tubes.

This division includes another most destructive woodborer, the Chelura terebrans, so devastating to piles and submarine timber all round the shores of Europe, but not recorded from other lands. Finally, we come to the minute aberrant forms of Dulichiida and C'aprellida (fig. 78), in ( which the body is reduced to a slender

elongated cylindrical FIG. 78.-Caprella tuberculata, Guerin; south form, the thorax hav

coast. (Spence Bate.)

ing only about six somites (one being absent and two soldered together), and the abdomen being quite rudimentary. They have long antennæ and feet, all fitted for climbing and holding on by. Their singular appearance has caused them to be called "spectre shrimps."

2

bidens, Portland Roads. 2. Cyamus

With these aberrant forms are associated the Cyamida (fig. 79), a family which affix themselves by their strong recurved legs to the rough 1 portions of the Cetacea upon which they feed. The feet are all prehensile; the third and fourth somites bear the branched or simple branchiæ. The abdomen, as in the Caprellida, is rudimentary; the eggs and young are sheltered FIG. 79.-1, 8 Cyamus Thompsoni, by four broad lamellar plates, Gesse found attached to Hyperoodon developed from the append- oralis, Vauzeme, found attached to ages on the under side of the common whale. (Spence Bate.) body of the female. Spence Bate and Westwood have figured five species. They approach in many respects to the Pycnogonidæ, which also live parasitic on Cetacea (see ARACHNIDA, vol. ii. p. 276-77), but we must not attempt to discuss their affinities here. A fragment of a presumed Amphipodous Crustacean has been described by the writer from the Upper Silurian (the Necrogammarus Salweyi) another, the Gampsonyx fimbriatus, occurs in the Ccalmeasures of Germany, Bohemia, and America. Mr Spence Prosoponiscus problematicus, its modern living representaBate has described one from the Permian of Durham, the tive, the Sulcator, making peculiar tracks upon cur shores today like those met with upon the surfaces of slubs cf

3 Spence Bate and Westwood (Sessile-eyed Crustacea, vol. iii. p. 311-328).