GASTROCOPTA, NORTH AMERICA, WEST INDIES. 51 



north of the S. P. Railroad close to where it enters Maricopa 

 Co. from the east, type loc. ; 5 miles south of Jerome, Yavapai 

 Co. (Ashmun). 



The localities of media are west of all those known for O. 

 dalliana, but its range seems to be overlapped by the eastern 

 extension of bilamellata. Its structural characters are be- 

 tween the two. 



14. GASTROCOPTA BILAMELLATA (Sterki and Clapp). PL 8, 

 figs. 1 to 4. 



"Shell small, slender, cylindrical or slightly attenuated 

 above, with an obtuse apex, perforate ; whorls 51/2, sub- 

 equal, the apical ones comparatively large ; colorless to pale 

 or reddish-horn (so far as can be seen from drift specimens), 

 transparent; surface shining, with very fine, crowded, sub- 

 regular striae, on the apex microscopically rugulose ; the last 

 whorl ascending above, somewhat flattened at the base close 

 to the aperture, keel-like further back, somewhat flattened 

 over the palate, with a slight to strong, not sharp, crest be- 

 hind the margin, with two spiral impressions, one over the 

 lower palatal and another near the base ; aperture broadly 

 elliptical to almost circular, peristome continuous or its ends 

 closely approximate and connected by a raised callous, well 

 everted, with a slight to rather strong lip thickening ; lamellae 

 and plicas, parietal and angular, well differentiated, con- 

 nected, large, the angular connecting with the peristome ; 

 columellar complex, with a lower axial and an upper hori- 

 zontal part; ' basal ' a short, transverse lamella, rather 

 abrupt ; lower palatal far remote from the margin, but visible 

 in front view, rather long, lamellar, thin ; upper palatal some- 

 what less deep-seated, close to the lower, somewhat oblique, 

 shorter. 



"Alt. 2-2.4, average 2.2, diam. 0.9 mm.; aperture alt. 0.8 

 mm. Soft parts not seen" (Sterki). 



Arizona : foothills of Plumosa Range, about 8 miles east of 

 Quartzsite, Yuma Co., in drift (type loc.; G. S. Hutson) ; 

 Salt River drift, Tempe, Maricopa Co. (Pilsbry and Ferriss) . 



Bifidaria bilamellata STERKI and CLAPP, Nautilus, xxii, 



