1905.] AMPHIBIA^^S AND REPTILES, 227 



Aglyplious Coluhrince. — Obviously with an archaic ISTearctic 

 centre. There is a gradual change from North to South. 



1. Northerners which send a few species only into Centi-al 



and still fewer into South America*, while none reaches 

 the Antilles : Trojndonotus, Ischnognathus, Contia *, 

 Ficimia, Coluber, Sjnlotes, Pittrophis, CoroneUa^ . Here 

 also Zamenis. 



2. Central Americans, from the Mexican Tierra Calienteinto 



South America and into the Antilles ** : Urotheca **, 

 Dromicus **, Drymohms **, Lejotophis **, Bhadinea, 

 Streptopliorus. 



3. Essentially Southerners with their present centre in South 



America, extending northwards into Mexico, but not 

 into the Antilles : e. g. Atractes, Tro2ndodipsas, Dirosema, 

 GeopMs, Xenodon. 



O'pisthoglyphous Coluhrince. — Essentially South and Central 

 American, Avith many mostly arboreal forms in the hot countries 

 of Mexico, wdiilst 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. 



Crotalince. 



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 

 TyjMopidai and peiliaps Glauconndoi and have received those 

 Boas and Agiyphous 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 soutlnvards 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 north- 

 wards into or even beyond Mexico, just as some obviously 

 Nearctic species are still extending southwards. 



Distribution op Mexican Species according to Altitude. 



Our knowledge of the fauna of North-western, Northern, and 

 North-eastern Mexico is too imperfect. The calculations are 

 therefore I'estricted 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 



15* 



