GASTROCOPTA. 7 



present; palatal folds developed (except in B. corticaria). 

 Lip well expanded. 



The foot is short; tentacles are rather short but distinct. 

 The sole is not divided longitudinally, and in progression 

 shows few muscular waves over its whole width. 



Type, G. acarus (Bens.). 



Distribution, nearly world-wide, in tropical and temperate 

 regions, but wanting in the recent European fauna. 



Gastrocopta. is essentially a hexodont Pupillid of oblong- 

 conic, subcylindric or ovate shape, in which the angular and 

 parietal lamellae converge and are connected ~by a callus in- 

 wardly, or become completely concrescent into a single sin- 

 uous lamella; the shell being small, thin, usually corneous, 

 and without lamella? in youth. 



The affinities of the species are determined by the mode 

 and degree of specialization of the lamellae and plicae. Spec- 

 ialization has been in two directions, which might be termed 

 negative and positive : 



(1) In some forms the teeth have been reduced in size and 

 number. Thus Privatula (G. corticaria) has lost the palatal 

 and basal plicae; in Vertigopsis (G. pentodon) the lamellae of 

 the parietal region have degenerated. 



(2) In other forms the lamellae, and more rarely the plicae, 

 are enlarged and specialized in shape, producing very com- 

 plicated apertures. 



In either series, accessory lamella? and plicae may be de- 

 veloped; they have little significance. 



Many species of Gastrocopta have the shell daubed with 

 dirt, attached by the mucus of the animal. Bothriopupa has 

 the same habit, but not our other American genera such as 

 Pupoides, Pupilla and Vertigo. Species and individuals are 

 most numerous on limestone terranes, or where the rock con- 

 tains considerable lime, living under stones or wood in grassy, 

 often sunny places, or in the shade on leaves and dead wood. 

 G. corticaria is commonly found on the trunks of trees, not 

 far from the ground. 



Gastrocopta approaches more nearly to a world-wide dis- 

 tribution than any other genus of the family Pupillida:. If 



