54 GASTROCOPTA, NORTH AMERICA, WEST INDIES. 



Type G. acarus (Bens.). 



Distribution, tropical and warm temperate portions of 

 America and Africa; Mascarene Is., Ceylon, the Philippines 

 and Hawaiian Islands. 



This group is developed in warm temperate and tropical 

 America, chiefly from the southern tier of states in the United 

 States to the Argentine Republic. They are the common and 

 abundant Pupse of much of these regions. Besides its distri- 

 bution in North and South America (species nos. 16 to 32), 

 where the greatest number and variety of species have been 

 found, typical Gastrocoptas inhabit Africa and the islands 

 in the Indian Ocean (species nos. 66 to 76), Ceylon and per- 

 haps India (species 77, 78), the Philippines and Oahu (spe- 

 cies nos. 86, 87). 



Gastrocopta appears to be related to Immersidens, but not 

 closely to the northern group of subgenera, Albinula, Sinalbi- 

 nula, etc. Among other significant differences, the position 

 of the basal plica may be noted. In Albinula, Sinalbinula and 

 Vertigopsis this plica is more or less obviously subcolumellar 

 in position; so much so that many describers have referred 

 to it as a second or inferior columellar tooth. In Gastrocopta 

 and Immersidens it never assumes a subcolumellar position. 



The species are much alike and partly difficult to distin- 

 guish, both from the absence of salient differential charac- 

 ters, and in some cases from the resemblance of simplified 

 members of different specific stocks. They are especially vari- 

 able in the development and prominence of callosities or 

 tubercular teeth below and above the eolumellar lamella, and 

 the prominence of the crest behind the outer lip, and are 

 somewhat variable in the degree of concrescence of the angu- 

 lar and parietal lamellae. Moreover, a number of the species 

 have been so imperfectly defined that positive decisions are at 

 present unattainable. 



Key to North American and Antillean Species. 



a. Lip distinctly or heavily calloused within. 



b. Form distinctly tapering; callous of the lip heavy, 

 c. Corneous or whitish, the lip white. 



G. rupicola, no. 17. 



