DISTRfBUTT'jy OF TPIE LAND AND FRESH WATER MOL- 

 LUSKS OF THE WEST INDIAN REGION, AND THEIR 

 EVIDENCE WITH REGARD TO PAST CHANGES OF LAND 

 AND SEA. 



By Charles Torrey Simpson. 



Aid, Depart me lit of Molliiskn. 



The West Indian arcliipeliigo lies almost wliolly within tlie tropics, 

 and extends from latitude lO'^ to 27° 30' north, and between longitude 

 59° and 85° west, and eml)races an area of about 9."),(K)0 square miles. 

 It presents an example of an astonishingly rich and diversitied land 

 snail fauna; in fact no other area of the globe of equal extent can 

 be compared with it. Within this region there are about 1,000 

 species of terrestrial inollusks, belonging to some 65 genera, a num- 

 ber almost as great as that found on the mainland of the entire 

 continent of America. The structure of the Greater Antilles is very 

 different from that of the lesser archipelago,* or from that of the 

 Bahama grou]). Each of the lour large islaiuls is believed to consist 

 of a nucleus of igneous and metamorphic rock, that forms the sum- 

 mits of the higher mountains, which are flanked by Cretaceous, Tertiary, 

 and I'ost Tertiary beds. The loftiest peaks of eastern Cuba attain a 

 height of 8,400 feet; those of Haiti and Jainaica a little over 7,000, 

 wliile Puerto Rico's greatest elevation is slightly less than 4,000 feet. 

 These mountain chains run. for the most part, lengthwise of the islands, 

 and from a glance at the map one can not help thinking that Haiti — 

 which looks something like an enormous letter Y, with one arm i)()int 

 ing toward Cuba, the other in the direction of Jamaica, while the 

 stem is directly in line with Puerto Rico — is a sort of connecting link 

 in the great archipelago. The channel between Cuba and Haiti is 875 

 fathoms in depth, the one dividing the latter island from Jamaica is 

 about 1,000, while that between Puerto Rico and San Domingo is 200 

 fathoms deep. 



*In tbe followiug pages the term Lesser Antilles or Windward Islands will be used 

 to include all the islands south of tbe Anegada Channel, beginning with Sombrero, 

 Anguilla, and St. Martin, and including Trinidad. The islands lying north of and 

 along the coast of Venezuela will be called the Leeward Group. Cuba, Haiti, 

 Jamaica, Puerto Rico, the Isle of Pines, and the Virgin Islands are included in the 

 general terra C4reater Antilles. 



Proceedings of the U. S. National Museum, Vol. XVII, No. 1011. 



423 



