436 WEST INDIAN MOLLUSES— SIMPSON. vol. xvu. 



Tvliile the one between the hitter ishmd and Puerto Rico carries but 2G0 

 fathoms. Supposing these islands to have been united at a former time, 

 tlien during- a period of gradual subsidence, Jamaica would be separated 

 sometime before the rest of the Antillian island would be broken 

 up, then Cuba, would be isolated, while Haiti and Puerto llico would 

 remain united for a longer time. The distribution and character of the 

 land-snail fiuinas of these islands agree exactly with just what would 

 be the result of such a subsidence and separation. 



When this region was revisited with a period of elevation — a i)eriod 

 which seems to be still in 5)i"ogTess — a large area of limestone was 

 uncovered, which, with a warm climate and an abundant rainfall, was 

 soon overspread with forests and cut into innumerable gullies and 

 ravines, furnishing the very best of conditions for the de^•elopment of 

 forms, and the multiplication of individual land-snads, and the genera 

 and grouj)S which had been huddled together on the reduced i>eaks 

 of these islands gradually spread out and took ])ossession of the new 

 territory. 1 regard these facts as the ])robable explanation of the 

 enormous development of terrestrial molluscan life in the Greater 

 Antilles. 



RELATIONS OF THE LAND AND FRESHWATER MOLLUSCAN FAUNA OF 

 THE GREATER ANTILLES WITH THAT OF MEXICO AND CENTRAL 

 AMERICA. 



It is, I believe, acknowledged that the terrestrial and Huviatile mol- 

 luscan fauna of the Greater Antilles has certain rather intimate relation- 

 ships with that of the adjoiningmainlaudof Central America andMexico. 

 The great genus Glandina, which at present has its metropolis in the 

 latter region, is represented in the archipelago by a number of species 

 almost equal to that found on the continent. Only a single recent 

 species exists outside of the warmer parts of America — 6'. algira of 

 southern Europe and northern Africa — though the genus is abundantly 

 represented in the Tertiary beds of Europe. Not only is it found in 

 the Greater Antilles, but several of the minor groups are there repre- 

 sented. The section Oleacina is mostly Antillean, but has 4 species on 

 the mainland; Varicella has 7 on the continent and 21 in the islands; 

 Melia has two species in Mexico and 13 in the archipelago, and the 

 section Glandina, which is abundantly represented on the mainland, 

 has a single species in Haiti. StreptostyJa, another JNIexican genus, has 

 Antillean species — lin Cuba, 2 in Haiti, and 3 in Puerto Pico. Vohi- 

 ta.ris, a third group belonging to the American mainland, has 1 species 

 in Cuba and another in Haiti, and Orthalicus, whose metropolis is in 

 the warmet parts of America, has 1 species common to Cuba and 

 Jamaica. 



Fischer and Crosse* divide the Stenogyrida^ into two subfamilies — 



' Miss. Sci. au, Mexique, 7th part, p. 585. 



