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Borneo, Java, Amboyna, and South Australia ; Phyton has one species in North America and the other in Ceylon; Philagetes has 2 in South Africa, and 1 in Malacca: Toxotus abounds in North America and Europe, with one species away in Madagascar. Leptura is also North Temperate, but has a species at the Cape, one at Singapore, and a third in Celebes. Necydalis has species in North and South America, Europe, and Australia. Hylotrupes has 1 species in North America and Europe, and 1 in Australia ; Leptocera prefers islands, being found only in Ceylon, Madagascar, Bourbon, Batchian, the New Hebrides, New Caledonia, and North Australia ; Hathliodes is Australian, with 1 species in Ceylon; Schcenionta has 3 Malayan species, and 1 in Natal. Many other cases equally curious could be quoted, but these are sufficient. They cannot be held to indicate any close relation between the distant countries in which species of the same genus are now found, but perhaps serve to remind us that groups of great antiquity, and probably of great extent, have dwindled away, leaving a few surviving relics scattered far and wide, the sole proofs of their former predominance.
General Observations on the Distribution of Coleoptera. We have now passed in review six of the most important and best known groups of the Coleoptera or Beetles, comprising about 2,400 genera, and more than 21,000 species. Although presenting certain peculiarities and anomalies, we have found that, on the whole, their distribution is in very close accordance with that of the higher animals. We have seen reason to believe that these great and well-marked groups have a high geological antiquity, and by constantly bearing this fact in mind, we can account for many of the eccentricities of their distribution. They have probably survived changes of physical geography which have altogether extinguished many of the more highly organised animals, and we may perhaps gain some insight into the bearing of those changes, by considering the cross relations between the several regions indicated by them. On carefully tabulating the indications given by each of the groups here discussed, I arrive at the following approximate result. The best marked affinities between the regions are those between the Nearctic and Palæarctic,—the Oriental and Australian,
—the Australian and Neotropical,—which appear to be about equal in each case. Next comes that between the Ethiopian and Oriental on the one side, and the Ethiopian and Neotropical on the other, which also appear about equal. Then follows that between the Nearctic and Neotropical regions; and lastly, and far the least marked, that between the North Temperate and South Temperate regions. That the relation between the Ethiopian and Neotropical region should be so comparatively well marked, is unexpected; but we must consider that in such a comparison as the present, we probably get the result, not of any recent changes or intermigrations, but of all the long series of changes and opportunities of migration that have occurred during many geological epochs,-probably during the whole of the Tertiary period, perhaps extending far back into the Secondary age.
It appears evident that Insects exhibit in a very marked degree in their actual distribution, the influence both of very ancient and very modern conditions of the earth's surface. The effects of the ancient geographical features of the earth, are to be traced, in the large number of cases of discontinuous and widely scattered groups which we meet with in almost every family, and which, to some extent, obscure the broader features of distribution due to the period during which the barriers which divide the several primary regions have continued to exist. And this, which we may consider as the normal distribution, is still further obscured in those cases where the barriers between existing regions are of such a nature as to admit of the free passage of insects or their larva in a variety of ways, and (wbat is perhaps of more importance) in which the physical features on both sides of the barrier are so nearly identical, as to admit of the ready establishment of such immigrants as may occasionally arrive. These conditions concur, for some families of insects, in the case of the Oriental and Australian portions of the Malay Archipelago; and it is there that the normal distribution has been sometimes greatly obscured, but never, as we have sufficiently shown, by any means obliterated.
AN OUTLINE OF THE GEOGRAPHICAL DISTRIBUTION OF MOLLUSCA.
THE Mollusca being for the most part marine, it does not enter into the plan of this work to go into much detail as to their distribution. The orders and families will, however, be passed briefly in review, and all terrestrial and fresh-water groups discussed in somewhat more detail ; with the object of showing how far their distribution accords with that of the higher animals, and to what extent the anomalies they present can be explained by peculiarities of organisation and habits. If the views advocated in our fifth chapter are correct, the regions there marked out must apply to all classes of animals; and it will be the task of the students of each group, to work out in detail the causes which have led to any special features of distribution. All I can hope to do here, is to show, generally and tentatively, that such a mode of treatment is possible; and that it is not necessary, as it is certainly not convenient or instructive, to have a distinct set of “Regions” established for each class or order in the Animal and Vegetable Kingdoms.
For all the Marine groups I have merely summarised the information contained in Mr. Woodward's Manual of the Mollusca, but in the case of the Land Shells. I have consulted the most recent general works, and endeavoured to give an accurate, though doubtless a very incomplete, account of the most interesting facts in their distribution. As their classification is very unsettled, I have followed that of the two latest great works, by Martens and Pfeiffer.
Family 1.-ARGONAUTIDÆ. “Paper Nautilus.” (1 Genus,
4 Species). DISTRIBUTION.—Open seas of all warm regions. Two species fossil in Tertiary deposits.
FAMILY 2.—OCTOPODIDÆ. “ Polypi.” (7 Genera, 60
Species). DISTRIBUTION.—Norway to New Zealand, all tropical and temperate seas and coasts.
FAMILY 3.-TEUTHIDÆ. “Squids or Sea-pens." (16 Genera,
102 Species.) DISTRIBUTION.—Universal, to Greenland ; 2 other genera are fossil, in the Lias and Oolite.
FAMILY 4.-SEPIADÆ. “Cuttle Fish.” (1 Genus, 30 Species).
DISTRIBUTION.—All seas : 4 other genera are fossil, in Eocene and Miocene deposits.
FAMILY 5.-SPIRULIDÆ. (1 Genus, 3 Species). DISTRIBUTION.—All the warmer seas.
FAMILY 6. — BELEMNITIDÆ. Fossil. (6 Genera, 100
Species). DISTRIBUTION. — Lias to Chalk in Europe, India, and North America.
FAMILY 7.-NAUTILIDÆ. (1 Genus, 3 Species, Living; 4
Genera, 300 Species, Fossil). DISTRIBUTION.—Indian and Pacific Oceans; and the fossil species from the Silurian Period to the Tertiary, in all parts of the world.
(8 Genera, 400
FAMILY 8.—ORTHOCERATIDÆ. Fossil.
Species). DISTRIBUTION.—Lower Silurian to Lias.
FAMILY 9.-AMMONITIDÆ Fossil. (14 Genera, 1100
Species). DISTRIBUTION.—Upper Silurian to Chalk. Found at 16,000 feet elevation in the Himalayas.