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Show 696 MR. ST.GEORGE MIVART ON PLETHODON PERSIMILIS. [June 27, That a Newt from the south-eastern coast of Asia should resemble some North-American tailed amphibian could not have been so surprising, considering the American affinities of the Japanese forms; but that a species from Siam proper should resemble almost completely a genus otherwise exclusively North American and possessing no representative in the Palaerctic region* was a circumstance truly remarkable. Mr. Wallace has indeed suggested an explanation (by means of certain presumed geographical mutations f) of the discrepancy existing between the ophidian and batrachian populations of Japan ; but it seemed to m e difficult to account in any similar way for the phenomenon under consideration. It is true that though Plethodon is unrepresented in the Old World, unless by the so-called Pl. persimilis, yet the North-American genus Spelerpes has a near relative in Europe in the Geotriton genei of Tschudi J, and has recently been extended to the Neotropical region by Professor Peters § ; yet this hardly lessens the anomaly presented by the appearance of such a genus as Plethodon in the true Indian region. Accordingly I applied to Dr. Giinther for any additional information I could obtain concerning the typical specimens. He at once, with great kindness, placed me in possession of facts which considerably altered the aspect of the question. Mr. Mouhot, from whom the specimens were received, terminated his collections in the mountains of Laos, a very lofty region, to the north-east of Siam proper. The last specimens received from Mr. Mouhot were from that locality, and were without any notes, having been brought down after his death by his servants. The typical specimens of Pl. persimilis were received also without any notes; and Dr. Gunther entertains no doubt that they formed part of his last collection, i. e. that they came from the Laos Mountains. Supposing, as I have little doubt, that such was really the case, then the probability of finding American forms is largely increased, as we are, in these mountains, no longer in Siam proper, and, moreover, at an altitude such as fairly to warrant the expectation of the appearance of Palaearctic animals. That Japanese forms (i. e. Urodela allied to certain American kinds) should here make their appearance would not then be so surprising, the more so as Dr. Giinther informs me that the reptiles of the island of Formosa have considerable American affinities ; and though Newts have not yet been * Dr. Gunther, in his highly interesting and instructive paper on the " Geographical Distribution of Reptiles," says, speaking of Batrachians, " Palaearctic and Nearctic regions resemble each other more than any third" (P.Z. S. 1858, p. 390). t Nat. Hist. Review, vol. iv. 1864, p. 114. t Batrach. pp. 59 & 94, t. 2. f. 3. § Namely his Spelerpes ((Edipus) adspersus from Bogota (Monatsberichte der k. p. Akad. der W . z. Berlin, 1863, p. 468). But as allied forms are being discovered in the tableland of Mexico (e. g. Spelerpes cephalicus, S. osculus, and 5". lineolus, Cope, Proc. Acad. Nat. Sc. Philad. 1865, pp. 196,197), it is not improbable that other species will be found to have extended into, or to be represented by modified descendants in, the mountain-regions of Northern South America. |
