400 PROCEEDINGS OF THE ACADEMY OF [1899. 



places. Surface glossy, sculptured with unequally spaced longitu- 

 dinal grooves, and showing a few slight growth-Avrinkles in places. 

 General outlines of the spire straight. Apex obtuse. Whorls 9 

 to 9^, the earlier ones quite convex, the later four or five somewhat 

 flattened. Aperture small, ovate, the outer lip a trifle curved 

 forward in the middle; columella slender, concave. 



Alt. 7, diam. 1.9, longest axis of aperture 1.6 mm. 



Alt. 7, diam. 1.7, longest axis of aperture 1.6 mm. 



Diente, near Monterey, State of Nuevo Leon, Mexico. 



Similar in sculpture and color to Opeas odiosum, but perceptibly 

 more slender in the spire, with smaller apex. These two species 

 have the general form of Opeas subula, but diflfer totally in sculp- 

 ture; they are also more brilliant and more transparent. The 

 columella is not at all twisted, and there is no trace of a basal 

 notch or truncation. This species, of which about fifteen speci- 

 mens were obtained, is named in honor of Mrs. Mary C. Rhoads. 

 Bifidaria prototypus n. sp. 



Shell small, subcyliudrical, somewhat taperiug above, brownish 

 corneous, thin. Whorls 5, convex; apex obtuse. Aperture 

 truncate-oval; peristome expandfd. Teeth : the parietal bifid, 

 composed of two lamime, that on the light running outward to the 

 posterior termination of the outer lip, more or less united at its 

 inner end with the left lamina, which is more deeply seated, and 

 enters deeply; a rather high tooth at the middle of the columella; 

 and a similar but smaller and short denticle moderately remote 

 from the lip-edge, at the junction of the outer with the basal walls 

 of the aperture. Usually there is a minute denticle above the 

 last-described denticle. 



Alt. 2.5, diam 1 mm. 



Huingo, State of Michoacan, Mexico. 



This species has the general appearance of Pupa riipicola, but 

 differs markedly in dentition. There are only two denticles within 

 the outer lip, none at the base of the columella. The parietal 

 armature illustrates clearly the origin of the bifid fold of the 

 Bijidarke of the United States, retaining the ancestral form more 

 than any American species I have examined. There are two folds, 

 one to the right and more emerging, the other to the left and more 

 deeply entering ; the two more or less connected by a callus at the 

 inner termination of the ri":ht tooth. 



