GASTROCOPTA, NORTH AMERICA, WEST INDIES. 49 



13. GASTROCOPTA DALLIANA (Sterki). PL 8, figs. 5 to 9. 



"Shell minute, ovate-turriculate, perforate-rimate, pale 

 horu-colored, translucent ; apex somewhat obtuse ; whorls 5, 

 regularly increasing, convex, with the suture deeper between 

 the upper than the lower whorls ; the last whorl ascending at 

 the aperture, compressed at the periphery, especially so 

 toward the aperture, with a slight, shallow crest-elevation, its 

 base narrow except just behind the aperture, where there is a 

 slight depression ; surface with very fine, crowded striae ; 

 aperture equaling a little over one-third of altitude, almost 

 as wide as high, rounded below, with three almost equal angles 

 above, margins approximate, somewhat extended upward and 

 connected by a slight, straight callous, somewhat everted, 

 especially below, without a thickened lip. Lamellae and folds: 

 angular and parietal rather large, connected but distinct, the 

 former ending at the margin; a nodule-like inf raparietal ; 

 columellar rather large, lamellar, horizontally encircling the 

 somewhat projecting colurnella; basal transverse (radial) on 

 the impressed part of the base, short lamellar, abrupt; pari- 

 etal folds approximate, the superior rather short, the inferior 

 longer, deeper in the throat, somewhat oblique. Alt. 1.6 to 

 1.8, diam. 0.8 to 0.9, apert. alt. 0.6 mm." (Sterki). 



Southeastern Arizona: Nogales (type locality) and Santa 

 Rita Mts., Santa Cruz Co. (Ashmun) ; mouth of Sabino 

 canyon, Santa Catalina Mts., Pima Co. (Ferriss) ; Eagle 

 Creek, Graham Co. (Ferriss) ; Dragoon and Chiricahua Mts., 

 Cochise Co. (Pilsbry and Ferriss). 



Bifidaria dalliana STERKI, Nautilus, xii, Dec. 1898, p. 91. 

 PILSBRY and VANATTA, Proc. A. N. S. Phila., 1900, p. 593, pi. 

 22, f. 8. PILSBRY and FERRISS, Proc. A. N. S. Phila., 1910, 

 p. 143, f. 36a. ASHMUN, Nautilus, xiii, p. 14 (Ephraim can- 

 yon, Santa Rita Mts. ) . 



The shell is generally smaller than G. hordeacella, the an- 

 gulo-parietal lamella is conspicuously complex, and the basal 

 plica is transverse instead of entering. It is related to G, 

 bilamellata, from which it differs by the more cylindric shape, 

 the less diverging outer ends of the parietal and angular 

 lamellse, and the simple columellar lamella. The ends of the 



