ANTIQUITY OF SNAILS 267 



Oligocene Period, generic differentiation probably dates from 

 a much earlier time. Indeed, Dr. Pilsbry * is of opinion that 

 the first radiation of the Antillean group of the Urocoptidae 

 may have occurred on a Mesozoic Antillean land area. The 

 succeeding Eocene depression, he thinks, isolated various 

 branches of the existing stocks, western Cuba being pro- 

 bably the first fragment to be dismembered. It was probably 

 not until near the close of the Tertiary that continuity of 

 land was restored with east Cuba. Haiti and Jamaica would 

 seem to have remained united after both western and eastern 

 Cuba had seceded. Finally, these islands were widely 

 separated by the subsidence culminating at the end of the 

 Eocene, or in the beginning of the Oligocene Period. This 

 depression was again followed by an elevation in later Oligo- 

 cene times, and it is likely that there was a transitory connec- 

 tion between Jamaica and Haiti. Between the latter and 

 Cuba the land connection probably lasted longer, thus pro- 

 ducing the homogeneous distribution of several groups. It 

 is likely, says Dr. Pilsbry, that during this mid-Oligocene 

 elevation, the Haitian land included Portorico, the Virgin 

 islands and the islands of the Anguilla bank, that is to say, 

 some of the northern group of the Lesser Antilles. Dr. 

 Pilsbry argues that the presence of large fossil mammals of 

 South American type (Amblyrhiza and Loxomylus) in Plio- 

 cene deposits of Anguilla demonstrates that the whole Carib- 

 bean chain of islands was elevated into a ridge connected 

 with South America during the Pliocene Period. He likewise 

 expresses the opinion that the genus Brachypodella, one of 

 the Urocoptidae, extended its range westward to Yucatan. 

 Nevertheless, he contends that there is but scanty evidence of 

 any direct land connection between the Greater Antilles and 

 the mainland of Central America during the whole of Tertiary 

 time. 



Thus, while differing from Dr. Simpson on several minor 

 points, Dr. Pilsbry's careful researches confirm his view, 

 and that of many geologists, that originally there was a large 

 area of land of which the Antilles are the last remnants, and 

 that some time during the Tertiary Era almost the whole of 



* Pilsbry, H., "Manual of Conchology," XVL, pp. xx. xxiv. 



