TEIID LIZARDS OF THE GEXUS CXEMIDOPHOEUS 255 



lost ill CneinklopJKjru.s, others havc^ Itoeii further developed. Here, 

 as in the resemblances, the transition is gradual in most cases, so 

 no great gap or break between the two genera, or between munnus 

 and the other species of Cneitiidophorus really exists. 



As the preceding discussion indicates, Cnemidophonis is a special- 

 ized northern offshoot from Amelva, through an ancestral form sim- 

 ilar, at least, to the modern nmrinus. This last-mentioned entity 

 apparently owes its preservation, as does many another primitive 

 .species, to its island isolation. To-day nhurinKS occurs only on the 

 islands of Bonaire and Curacao, north of Venezuela. Between these 

 and the mainland — on the small island of Aruba — the closely re- 

 lated C. murium amhcmiii now occurs. On the mainland we find 

 C. Jemniscatiis le/nn/'scatus, another link in the genetic chain and an 

 obvious derivative of aimhensis. It is the Jemniscatus stock, rather 

 than that of the more ancient murhius, that appears to be the most 

 progressive element of its group. In fact, hm/dseafus-like stock, 

 similar, at least in most respects, to the modern leniniscatus, was 

 clearly ancestral to all of the remaining forms of Cnemidophonis. 

 At an early period this stock, after spreading over northern South 

 America, gave rise to a remarkably distinct southern derivative, C. 

 oceJJlfer, which now inhabits parts of Brazil, Bolivia, and Paraguay. 

 However, the closely allied subspecies of h/iw/scatus, nigricolor, 

 which now occurs on the coastal islands of the arc extending north 

 of Venezuela and east of Bonaire, no doubt originated in relatively 

 recent times, probably not earlier than the Pleistocene. The de- 

 tails of the relationships within the Jemniscatus group have been 

 given on pages 53 to 56. 



Athough the assignment of definite geologic age to the evolution- 

 ary events in the history of Cnemidophoi^vs is largely conjecture, 

 the following time relations allow an explanation that seems to fit 

 the facts so far as known. Northward migration of the ancestral 

 lemnisccdus stock was impossible in the early Miocene, if it existed 

 at that time, because of the presence of an extensive water barrier, 

 the Costa Kican-Panama portal. Later in the Miocene, just after 

 the closure of this portal, certain faunal elements from South 

 America were said to have spread from Central America to the 

 West Indies. Lemniscatibs may have started on this journey at that 

 time, for it is now found on Old Providence Island, but, if so, it was 

 apparently blocked from further eastward migration since it has 

 not been found on Jamaica or Hispaniola. 



As to the origins of the deppii., sexUneatus., and tessellatus groups, 

 there is some uncertainty, but it is very probable that the former 

 appeared first. The species deppii, the southermost representative 

 of its group, shows the least specialization from lemniscatios of all 



