212 UROCOPTIS, S. G. GONGYLOSTOMA. 



This is the most difficult group of Cuban Urocoptis, not 

 only because many of the species are very similar, but on 

 account of the numerous unfigured and not fully described 

 forms introduced by Arango. The key given below is to be 

 regarded as a first attempt. 



There is a regular and uninterrupted gradation in axial 

 structure from the two strong lamellae of the group of U. 

 elegans and U. crispula, to the single weak spiral thread of 

 the group of U. capillacea. 



In the group of U. elegans there is often a short third 

 lamella interposed between the other two. The upper 

 lamella is noticeably thicker than the lower one. In some 

 of the other groups the upper lamella also is thin. 



Key to Species of Gongylostoma s. str. 



I. Shell ribbed; uniform or with light ribs on a darker 

 ground; two axial lamellae (group of U. crispula). 



1. Sinistral. U. coronadoi, no. 88. 



2. Dextral. 



a. Two axial lamellae subequal, both stout. 



U. crispula, no. 87. 



&. Upper lamella decidedly thicker than lower. 



U. artemisice, no. 84. 

 c. Lamellae subequal, both thin. 



U. gutierrezi, no. 85; U. lirata, no. 86. 



3. Dextral, small with only one well-developed axial 

 lamella. 



a. Rapidly tapering above ; 12 to 15 x 3 mm., 



with 12-15 whorls. U. fusiformis, no. 104. 



1. Length 10 to 12, diarn. about 3 mm., with 



Sy 2 to 9 whorls. U. garciana, no. 108. 



II. Shell striate, the axis with two or three strong lamellae. 



1. Striae coarse but low, sometimes effaced on the 



convexity of each whorl. 



a. Small, about 11x3 mm., with 9%-ll whorls ; 



upper lamella obsolete above the last 4 whorls. 



1 U. distincta, no. 98. 



