Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/489

DISTRIBUTION.] REPTILES 471 region, and represented by five genera, which, if not peculiar to Tropical America, are at least confined to the New World, like Cencliris and Crotalus. The Reptilian fauna of tropical America thus shows relations to the other equatorial regions in three of its constituent parts only, viz., in the Chelydidee, Amphis- Isenidx, and Crotcdidx. It has the former type in common with Africa and Australia; but, whilst the presence of Trionyx on the African continent forms an important distinctive feature, the resemblance of South America to Madagascar is as great as, or even greater than, that to Australia, which lacks Testudo. On the other hand the Lacertilian fauna is essentially distinct from that of the Old World, with the exception of Amphisb&nidse, (and of species of Eublepharidse), whose presence in South America and Africa is a most remark- able fact, and very strong evidence of the former existence of intervening land. The Skinks and Geckos, which are generally distributed over the warmer parts of the globe, cannot come into consideration. The Snakes of Tropical America differ also much more from those of the Old- World regions than certain other portions of its fauna, as, for instance, its Batrachians and Freshwater Fishes. A distinct affinity with India is expressed only by the development of the family of Pit Vipers, the presence in both regions of numerous Tree Snakes, of species of the genus Geophis, of the family Tortricidx, &c., being less significant points of resemblance. But these resemblances are more than counterbalanced by the absence in South America of Lycodonts, Tropidonoti, Pythonidae, Eryddse. The African Ophidian fauna l is still further removed by CrotaMdse being entirely wanting and replaced by Viperidse. ; only a few genera, like Steno- stoma, Coronella, Leptodira, Dipsas, Ahsetulla, are examples in which species are found in both regions. In both Tropidonotus is almost absent. As all the innocuous Colubrine Snakes of Australia are derived from the Indian region, they form no part in a comparison between the Australian and South-American faunse. Of the other Ophidian types these regions have not a single genus in common, nor a family which would not be represented also either in Africa or India or both. 5. The North- American Region. While the Chelonians of the North-American or Nearctic region (in which, so far as this Reptilian order is concerned, Central America and the West Indies have to be included) are essentially different from those of South America, the Lizards and Snakes of both belong to the same family types, and pass in an unbroken series from the northern to the southern parts of the New World. In this region the Emydidse, have attained to as great a development as in the Indian, and are associated with a few representatives of Testudo and Trionyx. The species, which are altogether about fifty in number, and of which a few are common to the Central-American and North- American sections, are distributed as follows : Central America, A ._,, 2 including Mexico. * America. Testudo 1 fCistudo 1 1 Clemmys 13 10 Dermatemys 1 Macroclemmvs 1 1 Chelydra ". 2 1 Staurotypus 3 Aromochelys 2 '-Cinosternum 10 3 Trionyx 2 30 21 1 Of the relations existing between the Snakes of South America and Madagascar we have spoken above, p. 469. 2 In a Check-list published by the U.S. National Museum in 1883 dians. It may be seen from this list that no Chelydoid passes northward beyond the Isthmus of Panama ; the Chelonians of Central America belong exclusively to the Emydidx, which are represented by some thirty species ; the majority do not extend either into South or North America ; two of the genera, Dermatemys and Staurotypus are peculiar to it, and Cinosternum has its headquarters in this section. Neither Trionyx nor Testudo occurs. Proceeding beyond the Mexican boundary, we find still the Emydidee predominating, a few of the species of Central America ranging northwards into the United States ; distinct species of Clcmmys,* Cinosternum, Chelydra, &c. , appear, with the wonderful genus Macroclcmmys. An instance of the isolated occurrence of a Testudo ( T. polyphemus) is met with here ; and from the lower part of the Mississippi northward one of the most characteristic features of the North -American fauna makes .its appearance, viz. , two species of Trionyx, of which one at least follows the ramifications of that river northward and has found its way into Lake Winnipeg (51 N. lat. ). West of the Rocky Mountains Tortoises are scarce and of distinct species. In the West Indies the following species have been found : 1, Testudo tdbulata 2, Podocnemis dumeriliana ; 3, Emys concinna ; 4, E. decussata ; 5, E: rugosa. Of these the first two are identical with South-American, and the third with a North-American species, and, therefore, may be regarded as strangers which in compara- tively recent times have been introduced into the West Indies. On the other hand the last two are species peculiar to the islands, and, as they belong to a North- American generic type, clearly prove the pertinence of this island district to the northern continent, so far as Tortoises are concerned. The south-eastern parts of North America are inhabited Croco- by an Alligator which is specifically distinct and locally Lilians, separated from the southern species. The tropical Lacertilian and Ophidian faunae gradually Lacer- merge into that of the temperate north, and any boundary tilians line drawn between the north and south is more or less ^? _ p arbitrary. As a matter of fact so many truly tropical forms advance north of the tropic of Cancer (which by many authors is taken as the boundary line) that we are inclined to restrict the limits of this region to the district about the Rio Grande, whilst, on the other hand, the northern fauna extends to a lower latitude on the plateau of Mexico. Thus restricted, the North-American fauna includes about fifty species of Lizards, belonging to genera which with very few exceptions are already represented in Central America, or even farther southwards. By far the greatest number are Iguanidee, ; the Scincidx, Anguidse, and Tejidse, are represented by several, the Geckonidse by fewer species, whilst single species occur of the Amphisbxnidse, Aniellidx, Lepidophymidx, and Heloder- matidse, all Central-American types. In fact, North America does not possess one family of Lizards peculiar to it. 1 1 is worthy of notice that Lizards do not extend so far north- wards in the western as in the eastern hemisphere ; one species (Gcrrhonotus cceruleus) ranges into British Columbia, another into Minnesota (Eumeces septentrionalis), and a third into Massachusetts ( Eumeces fasciahis). Of Snakes about one hundred 4 species could be enumerated, with a proportion of 1 : 14 of poisonous to innocuous Snakes. All the families represented in this fauna occur also in tropical America, and there is a great agreement of the genera with those of the Cen- tral-American district, so that less than one-half can be considered as peculiar to this region, viz., Conocephalus, Carphophis, Contia, Cemophora, Hypsiglena, Chersodromtts, EMnochilus, Pituophis, Isclmognathus, CJtarina, Wcnona, Lichanura. Calamariidw and a much larger number of " North- American" terrestrial Chelonians is given, viz., forty-three. This is partly due to the southern boundary of " North America" being extended to the tropic of Cancer, partly to the fact that species are admitted in a different sense from those of the herpetologists of the Old World. By adopting these species a very erroneous impression would be created as regards the comparative numbers of the groups in the several regions. That check-list includes three species of Testudo, three of Cistudo, twenty-one of Emys and its subgeuera, five of Cinosternum, two of Aromochelys, one each of Macroclemmys and Chelydra, and six of Trionyx. 3 Emys blandingii may be erased from the list of species ; we have recently examined a specimen ; it is identical with Emys lutaria, and has evidently been introduced from Europe. 4 One hundred and eighty, according to some authors, who include a great part of Mexico, and adopt every variation to which a binomial term has been applied.