1905. ] AMPHIBIANS AND REPTILES. 227 
Aglyphous Colubrine.—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*, 
Meimia, Coluber, Spilotes, Pituophis, Coronella*. Here 
also Zamenis. 
. Central Americans, from the Mexican Tierra Caliente into 
South America and into the Antilles**: Urotheca**, 
Dromicus **, Drymobius **, Leptophis**, Rhadinea, 
Streptophorus. 
. Kssentially Southerners with their present centre in South 
America, extending northwards into Mexico, but not 
into the Antilles: e. g. Afractes, Tropidodipsas, Dirosema, 
Geophis, Xenodon. 
bo 
ise) 
Opisthoglyphous Colubrine.—Kssentially 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. 
Hlapince.—Neotropical, non-Antillean; but a few species of 
Hlaps range through Mexico, and one far into the United 
States. 
Crotaline. 
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 
Typhlopide and perhaps Glawconiide and have received those 
Boas and Aglyphous Colubrines which have near relations in 
Central and North-western South America, whilst Crotaline, 
Hlapine, and Opisthoglyphe ave 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 north- 
wards into or even beyond Mexico, just as some obviously 
Nearctic species are still extending southwards. 
DISTRIBUTION OF 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 restricted to those parts of Mexico which lie within the 
following lines: Mazatlan—Guanajuato— Mizantla, north of 
Jalapa in the State of Vera Cruz; and Coatzacoalcos, across the 
15* 
