REPTILES OF THE TRES MARIAS AND ISABEL ISLANDS. 



By LEONHARD STEJNEGER, 

 Curator, Division of Reptiles and Batrachians, U. S. National Museum. 



The present paper is based upon the collection made on the Tres 

 Marias and Isabel Islands in April and May, 1897, by E. W. Nelson 

 and E. A. Goldman. 



The surprising fact that the two expeditions which have collected 

 systematically in the Tres Marias brought liome the same number of 

 species, Forrer only collecting one snake, Diplotropis diplotropis, which 

 Nelson did not collect, and Nelson also aollecting only one snake which 

 Forrer did not obtain, viz, Boa imperator, seems to indicate that not 

 many more species than the 16 here enumerated are to be found in 

 these islands. 



It will thus be seen that the reptile fauna is an exceedingly poor one 

 and very disappointing in several respects. Thus most of the species 

 are common on the opposite mainland and generally distributed over 

 tropical Mexico and Central America. Then, again, it seems as if the 

 species are practically identical on all the islands of the group. This 

 would indicate a comparatively recent severance of the islands from 

 each other as well as from the opposite mainland of Mexico. 



It is worthy of note, perhaps, that there is absolutely no indication 

 of relation to the Cape Saint Lucas fauna of Lower California. The 

 only species occurring in both places is Phyllodactylus tubercnlosus, a 

 gecko of wide distribution, the presence of which is of absolutely no 

 moment in determining zoogeographicul relations. 



The only species whch seems to be peculiar to the islands is Cnemi- 

 dophorus mariarum. As will be explained more fully under the head 

 of this species, I have never seen a specimen from the mainland, and 

 those which have been recorded from there I regard as wrongly identi- 

 fied. However, the herpetology of the regions in question is too little 

 explored in detail to incline one to be dogmatic on a point like this, 

 but I may call attention to the fact that the swift which occurs on the 

 little Isabel Island, about halfway between the Tres Marias and the 

 mainland, is most certainly the same form which inhabits the latter, 

 viz, Cnemidophorus gularis mexicanus, and not C. mariariim, to which 

 it bears only a superficial resemblance. The species collected on Isabel 

 Island are referred to in the following paper without any number pre- 

 ceding the specific names. Mr. Nelson has contributed field notes on 

 some of the species, and these notes are given in brackets with his 

 initials at the end of the paragraph on the species to which they refer. 



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