GASTROCOPTA, NORTH AMERICA, WEST INDIES. 47 



sensis, but having carefully gone over larger series of both, 

 than I had seen in 1910, I fail to find any really connecting 

 examples. It stands nearer G. prototypus, but differs in the 

 shape of the columellar lamella, which is placed somewhat 

 obliquely, and descends inward as a whole, while in proto- 

 typus the whole lamella is horizontal but with a thickening 



c 



FIG. 16. G. oligobasodon. Ash canyon, Huachuca Mts. 



below its inner end, and another running upwards. The 

 lower palatal plica is far more deeply placed in oligobasodon 

 than in prototypus. In a large series of prototypus exam- 

 ined, none has a basal plica. In oligobasodon this fold is 

 rarely absent. 



12. GASTROCOPTA PROTOTYPUS (Pilsbry). PL 7, figs. 1 to 5. 



The shell is shortly rimate, subcylindric, slightly tapering 

 upwards, light brown, lightly striate, with but little gloss; 

 composed of 5% strongly convex whorls, the last without 

 any trace of a wave or crest behind the lip or on the neck. 

 The aperture is squarish-oval; peristome thin, well expanded 

 except near the upper end of the outer lip; insertions sep- 

 arated by nearly half the width of the mouth. Both angular 



