174 MATTHEW— RECENT DISCOVERIES OF 



tantly related to the spiny rats of South America (Echinomys). 

 Heteropsomys of Porto Rico is rather doubtfully related to this 

 group; certainly the affinities are distant. Jamaica is unknown 

 palseontologically. 



The fourth group, the rodents of the Amblyrhisa group, is lim- 

 ited to Porto Rico and Anguilla, that is to say, to the eastern end 

 of the east-west chain, and is w^holly extinct. Amhlyrhiza, the 

 largest, is quite gigantic for a rodent, about the size of the Capybara 

 or of the extinct Castoroides. Elasmodontomys of Porto Rico is 

 nearly the size of a beaver. Heptaxodon of Porto Rico is a smaller 

 form. These West Indian chinchillids are only distantly related 

 to the living Chinchillidse of South America, but they are quite 

 nearly related to the Megamys group of the South American 

 Pliocene. 



The fifth and sixth groups of mammals, the two insectivora, are 

 the most isolated of all the West Indian mammals, each having a 

 family to itself. They are not at all related to each other, and their 

 nearest relatives appear to be certain imperfectly known Eocene and 

 Lower Oligocene genera of North America. There are no autoch- 

 thonous insectivores at all in South America, save for the curious 

 little Necrolcstcs of the Miocene, which may have had something to 

 do with the Chrysochloridse, but certainly not with these West Indian 

 genera. On the other hand, insectivora occur in all the Tertiary for- 

 mations of North America, and were more abundant and varied in 

 the older Tertiaries. Micropternodus, of the Lower Oligocene, may 

 have been a distant ancestor of Solenodon, and several of the Eocene 

 soricoid genera from the Bridger show much resemblance to Neso- 

 phontes. But any exact relationship is to be regarded as provi- 

 sional, and by no means proven. 



Turning now to the reptiles, we find that the entire order of 

 chelonia is represented to-day by a single species of terrapin widely 

 distributed through the islands, found fossil in Cuba, possibly also 

 in the island Sombrero, and closely related to the yellow-bellied 

 terrapin of the United States. It belongs to a North American 

 group, its nearest fossil relatives are in the southeastern states, and 

 the few terrapins of Central and South America, which are prob- 

 ably rather late immigrants from North America, are less closely 



