BARBOUR AND NOBLE: LIZARDS OF THE GENUS AMEIVA. 421 
America was under water probably while this ancestral stock was 
migrating, but a short period of emergence or the presence of an ancient 
land mass joining north Central and northwest South America, but 
lying to the westward of the present Middle America, would have made 
possible the migration. This land mass, the existence of which we 
have suggested, has been postulated by various other writers on other 
grounds. The sinking of this area would then have left the A. wndu- 
lata allies free to distribute themselves in Central America as it as- 
sumed its present form and also to reach the Greater Antilles while 
they were in connection with Central America. The temporarily 
isolated South American stock then spread widely through the conti- 
nent and passed into Antillea extending to Haiti. Finally with the 
completion of the appearance of lower Central ‘America in its present 
form, we find it invaded by the Ameiva ameiva types in the form 
of A. praesignis, while western South America received some immigrant 
representatives of A. wndulata, which on reaching this region so pecu- 
liarly favorable for speciation in reptiles became transformed into the 
curious and hardly recognizable A. edracantha and A. bridges. The 
latter of these reached Gorgona Island off the Colombian coast. 
An alternative would have been to conclude that possibly the 
genus arose in Antillea and spread to Central and South America, but 
this seems hardly likely in view of the definite grouping of the species 
about the two prominent mainland types. 
Two other stocks remain to be mentioned, which show a somewhat 
-anomalous condition. The maynardi-wetmorei-polops group does not 
seem to show any very close relationship with the other species, and 
we can only conclude that these three very distinct species all represent 
‘chance survivors from some stock which once had a wider distribu- 
tion, but which has completely disappeared. The other anomaly 
is afforded by Ameiva bifrontata and its subspecies divisa. ‘These are 
not very dissimilar to Ameiva ameiva, but yet occur side by side with 
other races which are probably more closely related to Ameiva ameiva 
than either of them are. Whether these represent the survivors of a 
primary unsuccessful elaboration of Ameiva ameiva itself or are the 
remnants of some other stock, which in the same environment has 
come to look much like Ameiva ameiva, it is impossible to say. One 
gropes in the dark in treating all of this problem. It is even far from 
easy to surmise which are the more primitive types, while, of course, 
we know but little of skeletal variation within the group and there is 
no particular object to seek it out when it cannot be applied to palae- 
ontology. How sadly different are the opportunities for the mammal- 
ogist and the herpetologist in essaying studies of this sort. 
