xxii UROCOPTID^:. 



The land snails of about the same age found at Tampa, 

 Florida, belong to subgeneric or smaller groups still existing, 

 and with two exceptions now living. It may, therefore, be 

 considered certain that since numerous subgenerie groups of 

 land snails in essentially their modern forms were established 

 before the end of the Oligocene, the generic differentiation 

 dates from a decidedly earlier epoch. Probably the first adap- 

 tive modification or radiation of the Urocoptince took place 

 upon Mesozoic Antillean land area, the degradation of which 

 supplied materials for the late Cretaceous rocks of the pres- 

 ent islands. The succeeding Eocene depression isolated vari- 

 ous branches of the existing stocks, western Cuba being 

 probably the first fragment to be dismembered. Here Micro- 

 ceramus, a branch of the primitive radiation, survived ; Cock- 

 lodinella retained primitive features of axis and dentition, 

 also shown by the Haitian Autocoptis; and Gongylostoma 

 was evolved from the same stock. It was probably not until 

 near the close of the Tertiary that continuity of land was 

 restored with east Cuba, permitting some migration of these 

 groups eastward, and of Macroceramus westward as far as 

 Matanzas province, the reconstruction probably having pro- 

 ceeded from the west eastward. Haiti and Jamaica would 

 seem to have remained united after both western and eastern 

 Cuba had seceded ; and on the Haiti- Jamaica area the Brachy- 

 podella line was established, probably also the ancestral stock 

 of the notched or serrate-toothed genera. Finally, these 

 islands were widely separated by the subsidence culminating 

 at the end of the Eocene or in the beginning of the Oligocene. 

 During and subsequent to this subsidence most of the modern 

 subgenera of Urocoptis and Brackypodella were differen- 

 tiated. The remarkable number of minor phyla in these 

 groups may well have been due to independent local adaptive 

 radiations consequent upon the dismemberment of the main 

 islands into a number of smaller islets, due to the amplitude 

 of the subsidence, which carried the land far below its present 

 level. 



This depression was followed by elevation in the Oligocene, 

 according to Hill, probably sufficient to unite many of the 



