OP CONCHOLOGY. 151 



ON THE LAND AND FRESH-WATER MOLLUSCA OP 

 NICARAGUA. 



BY RALPH TATE. 



I. Introduction. 



The district in which the species enumerated in this paper 

 were collected comprises much of the south and central portions 

 of the republic of Nicaragua. 



Nicaragua presents two distinct types of soil, vegetation, and 

 climate, and, in a limited degree, the land shells are restricted 

 to one or other of the districts. These are : 



(1) Eastern District. — A low mountain chain trends in a 

 north-west and south-east direction through the central part of 

 the country; it is composed of diorites and schistoze rocks, 

 yielding by decomposition a stiff argillaceous soil, which is 

 clothed with a dense forest. This region extends to the Atlantic 

 seaboard, the climate of which is excessively humid. I collected 

 during a period of five months in that portion of this region 

 known as Chontales, which is situated at from 1500 to oOOO feet 

 above the sea level. 



(2) Western District. — Two parallel chains of volcanic moun- 

 tains occupy the western portion of Nicaragua. Here, from the 

 absorbent nature of the rocks and the comparatively little rain, 

 the chief vegetation is grass, but on the margins of the streams 

 and on some of the alluvial flats there is a limited growth of 

 timber trees. The general aspect of this region is that of sa- 

 vannas interspersed with wood. 



The mountain range bordering the Pacific is the primary di- 

 viding ridge, and between it and the median chain extends a low 

 valley stretching from the Gulf of Fonseca on the north into 

 Costa Rica on the south ; within this longitudinal valley is 



