HISPANIOLAN AND BAHAMAN ANNULARHDAE 183 



There is still another chain of cays belonging to the Great Bahama 

 Bank series, the Ragged Island arc, which extends from the middle of 

 the west side of Long Island to Cay Santo Domingo on Columbus Bank, 

 a distance of more than 130 miles. It drops off into profound water 

 at its outer limit. 



To the south, beginning with San Salvador and extending through 

 Rum, Crooked, Fortune, Acklin, Inagua, Caicos, and Turks Islands, 

 and also Cay Sal Bank, we have what one may describe as truncated 

 island cones rising from abyssmal depth upon the rim of which there 

 have been deposited, while submerged, the skeletal remains of ma- 

 rine organisms associated to form coral reefs. Some of these reefs 

 have emerged to considerable height. Cat island is listed by the Coast 

 Pilot as having an elevation of 400 feet. These groups of cays 

 form atolls, i.e., a rim of cays enclosing a shallow lagoon. The largest 

 and most perfect of these is Caicos, whose greatest diameter is more 

 than 70 miles. Crooked Island, Aklin Island, Fortune Island, and the 

 Fish Cays form the next largest atoll. The Cay Sal complex and Great 

 Inagua show the same structure. It is not surprising that one should 

 find a close relationship in the faunal elements inhabiting these rings 

 of islands. 



Throughout the entire range there is little land that would permit 

 the use of a plow. Most of the land is strewn with rocks, in whose 

 chinks most of the planting for domestic use is accomplished. This 

 means frequent shifting of fields and the destruction of the plant cover- 

 ing to furnish new fertile fields, a process disastrous to molluscan life. 



The native vegetation is largely a West Indian drift or wind-borne 

 element, and I believe that most of the molluscan fauna was similarly 

 derived in the long ago. 



With the exception of Cerion and Hemitrochiis, most of which climb 

 trees and shrubs, the land mollusks of the Bahamas are ground-dwellers, 

 seeking the protective cool shelter of rock crevices. Their transportation 

 from island to island might have been accomplished by individuals that 

 had sought refuge in hollow fallen trees, and these might have been car- 

 ried to sea by hurricanes and their accompanying floods and swept 

 thereby to a possible new haven on another island. Cerions, I have found, 

 can stand complete submergence for four and one-half days in salt water 

 and survive. Young shells attached to dead leaves may have likewise been 

 picked up by hurricanes and carried from island to island. 



The material studied includes that which has come to the National 

 Museum through the years from various sources. This, as well as the 

 collectors, are mentioned under each species with the Museum catalog 

 numbers. A large part was obtained by the author while a member 

 of expeditions of the Tortugas (Fla.) Marine Biological Laboratory 

 of the Carnegie Institution of Washington, which enabled him to 

 explore Andros, New Providence, and the adjacent islands. Gun Cay, 



