FOSSIL VERTEBRATES IN THE WEST INDIES. 173 



to the insular conditions. Their peculiar specializations and the 

 absence of any of the later and more progressive types of ground 

 sloths that spread all over the North American continent involves 

 isolation since that time, from North, South or Central America. 



The second group, the rodents of the Capromys type, affords 

 some contrast in its scope and relations. Instead of having four or 

 five very divergent genera quite wide apart structurally, we have 

 in the western Antilles, two closely allied genera, much closer in the 

 skeleton than they are superficially. They are the only native 

 mammals on the islands that are not on the verge of extinction ; 

 under natural conditions they would apparently be a very pros- 

 perous group. The cave records indicate they were rapidly progress- 

 ing in size and increasing in relative numbers in the Pleistocene. 

 And finally Procapromys of Venezuela, their nearest continental 

 relative, is quite closely related. They have not had time to diverge 

 very far from it in structure, although the record shows that they 

 were diverging. The surface inference is that this group was a 

 comparatively late arrival, perhaps early Pleistocene, perhaps late 

 Pliocene, clearly much later than the ground sloths. Yet they had 

 reached several of the western islands — Jamaica, Cuba, one of the 

 Bahamas, even Little Swan Island, a small islet off the coast 

 of Honduras. In Cuba- several species of Capromys now exist. 

 Geocapromys was formerly the principal or only type in Cuba, but 

 is now found only in Jamaica, Little Swan Island and Plana Key 

 on the Bahamas. In the eastern islands we find two genera less 

 closely related. Isolohodon of Porto Rico is extinct and Plagio- 

 dontia of Hayti is practically extinct ; these two are less closely re- 

 lated to the two western genera, but are regarded by Mr. Anthony 

 as the eastern representatives of the group. Systematic exploration 

 in the caves of Hayti would probably clear up the true relationship 

 of these eastern genera ; casual sketchy exploration or work under- 

 taken simply to get material and describe new species, is very likely 

 to destroy such evidence as exists on their palasontologic history. 



The third group, the Boromys group of rodents, is extinct (pos- 

 sibly a single survivor) and includes a number of species belonging 

 to two very closely related genera, doubtfully separable, one found 

 at several points in Cuba, the other from Hayti. It is rather dis- 



