624 Bulletin American Museum of Natural History [Vol. XLVI 



The latter two are peculiar to the island, the Verticaria being most closely 

 allied to the species on Carmen Island, while the similarity to the Car- 

 men Island fauna is increased by the species in common with it and the 

 peninsula. 



San Francisco Island has a single peculiar species, Verticaria francis- 

 censis. 



The fauna of Espiritu Santo Island comprises seven species: 



Sauromalus ater *V erticaria espiritensis 



Ula elegans Chilomeniscus punctatissimus 



Sceloporus zosteromus *Coluber barbouri 

 Sceloporus licki 



The peculiar species of snake is, I believe, more closely related to 

 the mainland form from which it is obviously derived than is the case 

 with the species peculiar to other islands. 



From Ceralvo Island, three species are known, Verticaria ceralbensis, 

 Sator grandsevus, and Ctenosaura hemilopha. The occurrence of a re- 

 lated but highly distinct species- of Sator on the island of Santa Cruz in- 

 dicates that this genus was formerly present on the peninsula, while the 

 divergence shown by these two insular species indicates a considerable 

 antiquity for the genus. I am unable to distinguish the Ctenosaura from 

 the peninsular species. 



Turning to the islands which I believe to be more closely related to 

 the Mexican mainland than to the Lower Californian peninsula, San 

 Esteban Island, in the middle of the gulf, has three species, Ctenosaura 

 hemilopha, Cnemidophorus estebanensis and Crotalus ?nolossus, at present 

 known from it besides the peculiar Sauromalus varius. Of these, the 

 first is found in Lower California, the Cnemidophorus is almost identical 

 with the C. melanostethus of Sonora, and the Crotalus is identical with a 

 Mexican form not found in Lower California. The relations of the 

 Sauromalus are not evident. As the question' of relations stands, there- 

 fore, it is two to one in favor of a Mexican relation of the island. From 

 the soundings of the gulf north and south of San Esteban, it is evident 

 that this is the most probable location of a connection of Lower Cali- 

 fornia with Sonora, if such a connection ever existed. 



The species known from Tiburon Island are the following: 



*Sauromalus townsendi *Cnemidophorus punctilinealis 



Crotaphytus wislizenii *Cnemidophorus disparilis 



*Crotaphytus dickersona- Micrurus euryxanthns 

 *Callisaurus ventralis in usilalus 



