24 Geographical Distribution 



little evidence of the existence of terrestrial species of shells. 

 The wonderful development both of genera and species on 

 islands, especially those the later geological movements of 

 which have been of elevation, do not at least negative the 

 indication above suggested. 



With respect to the Freshwater Shells of the West Indies, 

 which are by no meansnumerous, the distribution of the genera 

 shows the same connexion of the islands west of Portorico w4th 

 the northern, and of those east and south with the southern 

 continent of America, as do the Land Shells. Of Melania five 

 species occur in Cuba, none in the other islands ; one of Mela- 

 nopsis inhabits Jamaica. The only Unio in the islands is found 

 in Cuba. Two or three species of Ampularia are in Cuba, and 

 one in Jamaica, of North American type, while A. rugosa Lam., 

 of South America, occurs in Trinidad and Tobago, and A, 

 Knorri Phil, closely allied to A. cornu arietis f L., of New 

 Granada, also inhabits the former island. The species of other 

 genera, which are in the islands westward of Portorico, do not 

 generally extend to the islands east and south of it. Several, 

 however, have a remarkably wide distribution. Planorhis 

 lucidus Pf. occurs in Cuba, Jamaica, Portorico, and Guade- 

 loupe; Ancylus ohscurtis Hald., of North America, in Jamaica, 

 Portorico, St. Thomas, and Guadeloupe ; and Amnicola crystal- 

 Una Pf., which I found abundant in the river Magdalena, at 

 Barranquilla, New Gi-anada, inhabits Cuba, Jamaica, Portorico, 

 Yi^que, St. Thomas, St. John, Tortola, and Guadeloupe.* 



* The -wide distribution, on the continent of North America, of some of the 

 Uniouidoe is really wonderful. Mr. Isaac Lea mentions, in a communication made 

 in 1868 to the Philadelphia Academy, that some species common in the Ohio 

 River, as high up as Pittsburg, are found also in Moose River of Hudson's Bay, 

 62" N. ; in the Red River of the North, 50° :N. ; in Upper Missouri, 47® N. ; and 

 in the Big Sioux, 43° N. ; also as far south as Louisiana. 



The same remark applies to several terrestrial species of North America. 

 H. alternata Say is found from Labrador to Texas, and from the Atlantic ocean 

 to the Rocky Mountains. H. arborea Say, which, according to Beau, occurs in 

 Guadeloupe, inhabits an equally wide area, and extends even into New Mexico. 



