232 THE CHICAGO ACADEMY OF SCIENCES. 



Jaw: Rather wide, arcuated, ends slightly attenuated but 

 blunt. 



Radula formula: A+f +i+f+is-7> (H-I-II); teeth of 

 the usual form. 



Genitalia: Not known. 



Distribution: Eastern United States west to Minnesota 

 and south to Texas and South Carolina. 



Geological Distribution: Pleistocene; Loess. 



Habitat: Similar to corticaria. 



Fig. 63. 

 BIFIDARIA PROCERA Gould. (Binney, Fig. 354.) 



Remarks: This species may be known by its peculiar 

 aperture and five teeth. The parietal tooth is almost bifid and 

 turns in toward the tooth on the columellar wall. Procera is 

 very rare and has been found only in the southwestern part of 

 the western region. 



SECTION ALBINULA Sterki. 



"Shell oblong or conic-ovate or cylindrical, colorless." 

 (Sterki.) 



91. Bifidaria armifera Say, pi. xxx, fig. 15. 



Pupa armifera SAY, Journ. Phil. Acad., Vol. II, p. 162, 1821. 



Pupa armigera POTIEZ et MICHAUD, Galerie, Vol. I, p. 159, pi. xvi, 



figs. 1, 2. 



Bifidaria armifera ruidosensis CKLL., The Nautilus, Vol. XIII, p. 36, 

 1899. 



Shell: More or less cylindrical, obtuse, inflated, transpar- 

 ent; color very light horn, vitreous; surface smooth and shining, 

 lines of growth oblique, numerous, crowded; apex rounded, 

 almost concealed by the succeeding whorls, light horn color; 

 sutures well impressed; whorls six to seven, convex, the last 

 three being about equal in size, and above these the shell tapers 

 to an obtuse point; aperture ovate, narrowing toward the bend 

 {throat) where there are from four to six teeth, arranged as fol- 

 lows: a single, sometimes bifid, lamelliform tooth which begins 

 on the upper margin of the aperture, near the junction of the 



