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Show 1905.] AMPHIBIANS AND REPTILES. 227 Aglyphous Colubrince.-Obviously with an archaic Nearctic centre. There is a gradual change from North to South. 1. Northerners which send a few species only into Central and still fewer into South America*, while none reaches the Antilles: Tropidonotus, Ischnognathus, Contia*, Ficimia, Coluber, Spilotes, Pituophis, Coronella *. Here also Zcimenis. 2. Central Americans, from the Mexican Tierra Caliente into South America and into the Antilles ** : Urotheca **', Dromicus **, Drymobius **, Leptophis **, Rhadinea, Streptophorus. 3. Essentially Southerners with their present centre in South America, extending northwards into Mexico, but not into the Antilles : e. g. Atractes, Tropidodipsas, Dirosema, Geophis, Xenodon. Opisthoglyphous Colubrince.-Essentially South and Central American, with many mostly .arboreal forms in the hot countries of Mexico, whilst a few terrestrials extend also over the plateau and into the neighbouring United States. None Antillean. Elapince.-Neotropical, non-Antillean; but a few species of Elaps range through Mexico, and one far into the United States. Crotcdince. 1. Nearctic, especially Sonoran, xerophile, non-Antillean. Only one of them extending far into South America. 2. Neotropical, northwards into the Mexican Tierra Caliente, and into the Lesser Antilles. All this means that the Greater Antilles possess only the ancient Typhlopidce and perhaps Glauconiidce and have received those Boas and Aglyphous Colubrines which have near relations in Central and North-western South America, whilst Crotcdince, Elapince, and Opisthoglyphce are excluded. Further, this indicates that all these latter groups are post-Antillean, that they have extended southwards after the Antillean separation, have developed into the present tropical genera and species in Central and South America, and have then, eventually, most recently extended northwards into or even beyond Mexico, just as some obviously Nearctic species are still extending southwards. D i s t r ib u t io n o f M e x ic a n S p e c ie s a c c o r d in g t o A l t i t u d e . Our knowledge of the fauna of North-western, Northern, and North-eastern Mexico is too imperfect. The calculations are therefore restricted to those parts of Mexico which lie within the following lines : Mazatlan - Guanajuato - Mizantla, north of Jalapa in the State of Yera Cruz ; and Coatzacoalcos, across the |