1894. PROCEEDINGS OF THE NATIONAL MUSEUM. 435 



ooiifmed to Haiti, Puerto Rico, and tlie Balianias, a Cerion., not differ- 

 ing greatly in ai)])earance from G. incana, but wholly destitute of teeth, 

 a Cylindrella much like some of the recent Cuban species, and four 

 Bulimulus. The Miocene silex beds of Tampa and the Bowden marl 

 are believed by Dr. Dall to be nearly or quite synchronous. These 

 lorms, or their ancestors, may have migrated from Cuba across the 

 Bahama i>lateau and what is now the bed of the Gulf Stream. An 

 elevation of 344 fathoms would Join the Bahamas to Florida. 



If, then, a land connection existed between the Greater Antilles and 

 Central America during the period of elevation it wouhl not be difficult 

 for species of Glandina, t^ircptoHtyla, Volutaxis, Polygyra, Bulimulus, 

 Orlhalicus, Neocyclofiis, AmpuUarla, Pachycheilus, and Hemisinus — 

 genera whose metropolis is on the continent — to pass from the latter to 

 the former, or forms of widespread genera to migrate across to the 

 islands. And on such a landway it seems more i)robable that the 

 species of Thy.sanophora, Cylindrella, Macroceramus, Megalomastoma,, 

 Choanopoma, Cistula, Chondropoma, Tudora, Colohostylus, Adamsiella, 

 and Eutrochatelhij passed over to Mexico and Central America than 

 that they were carried by currents or any of the other agencies I have 

 mentioned. 



In the present state of our knowledge it is a little difficult to tell how 

 long the period of subsidence lasted, and we can not determine with 

 certainty how much of the area of the islands was submerged. An 

 elevation of some 3,000 feet above present sea level probably marks the 

 limit in Jamaica, as the stratified Miocene rocks are believed to reach 

 to about that height. 



In another part of this jiaper I have attempted to show something of 

 the close relationship of the molluscau faunas of the different islands of 

 the Greater Antilles. Jamaica, by the evidence of its land snails, 

 stands the most isolated of any of the islands ; Cuba is the next most so, 

 while those of Haiti and Puerto Rico are much more nearly related to 

 each other than to those of either of the first two. About 20 genera and 

 minor groups are confined to or have their metropolis in Jamaica; a like 

 number belongs to Cuba, 7 to Haiti, and 1 to Puerto Rico. Of the spe- 

 cial Jamaican groups, kSafjda, Plcxrodonte restrk'ted, Geomelania, Coloho- 

 stylus, Tudora, PtychocochUs, Adamsiella, Alcadia, Ijucidclla, and Stoas- 

 toma are abundantly represented throughout the island, and highly char- 

 acteristic, forming the major part of the land-snail fauna. In Cuba, 

 Liguus, Macroceramus, Cerion, Choanopoma, Gte)iopoma, and Chondro- 

 poma are generally distributed and characteristic ; while Carocolus and 

 Parthena stand in the same relation to the Haitian fauna. 



ISTow, as bearing directly on this subject, it may be mentioned that 

 the strait between Haiti and Jamaica is deeper than that between any 

 of the other islands, being nearly 1,000 fathoms in depth, that between 

 Cuba and Haiti is slightly more shallow, being only about 875 fathoms, 



