50 



GASTROCOPTA, NORTH AMERICA, WEST INDIES. 



lip are rather widely separated in dalliana, connected in bila- 

 mellata. 



The shell is very fragile and usually dirty, like all the 

 species of the same section. The inner end of the angular 

 lamella lies adjacent to the outer end of the parietal, with a 

 lower connecting callous between them. The parietal may 

 project slightly forward of the junction, or it may stop there. 

 Its inner end usually bends a trifle outward. The columellar 

 lamella is stout and transverse (pi. 8, fig. 8). Fig. 17 is from 

 a paratype. Length 1.8, diarn. 0.8 mm. 



In the Chiricahua and Dragoon mountains it is often 

 larger than the types, up to 2 mm. long, .85 wide. The basal 

 fold is usually longer than in the typical form. 



FIG. 17. O. dalliana. 



FIG. 18. O. bilamellata. 



130. G. dalliana media n. subsp. PL 8, figs. 10, 11. 



The shell is like dalliana in size, shape and fragility. It 

 differs by having a callous buttress below the inner end of the 

 columellar lamella (pi. 8, fig. 11). This is much less devel- 

 oped than that of G. bilamellata. The parietal and angular 

 lamellae are less intimately united, and the former reaches 

 further forward (pi. 8, fig. 10). The terminations of the lip 

 are rather widely separated, as in dalliana. 



Distribution. Arizona: Montezuma's Well, several miles 



