MOLLUSCA OF MICHIGAN— WALKER. 509 



Bulimus marginatus, Miles, Rep. Geol. Siirv.'^Mich., 236, (1861). 

 Pwpa jallax, Walker, Rev. Moll. Fauna Mich., 17, (1894). 



Not a common species. Reported from Berrien, Kent, Genesee, Monroe, 

 and Washtenaw counties. 



Genus BIFIDARIA Sterki. 



Shell small, umbilicus perforate, cylindrical, turriculate, conic or ovoid; 

 surface smooth, polished or finely striate or, rarely, finely ribbed; aperture 

 lateral, oval or sub-orbicular; contracted by one or more teeth on the pari- 

 etal wall and inner margin of the lip and columella; peristome expanded or 

 reflected; parietal lamella large and more or less distinctly complex, formed 

 by the fusing of the parietal and supraparietal lamellae; the columellar 

 lamella also generally somewhat complex; the typical inferior and superior 

 palatal lamellae are generally present and as a rule deep seated, never reach- 

 ing the margin. 



Animal, jaw and dentition as in Pupilla. 



Fig. 129. Animal of B. tappaniana. (Binney.) Fig. 130. Jaw of B. tappaniana. (Binney.) 



Fig. 131. Dentition of B. tappaniana. (Binney.) 

 KEY TO THE SECTIONS OF BIFIDARIA* 



I. Parietal and angle lamellae very short, small and tuberculif orm ; no 



palatal folds ; shell cylindrical Privatula, 



II. Parietal and angle lamellae elongate, more or less united, either by a 

 callous ridge, or so extensively as to appear like a single sinuous, 



or emarginate lamella Alhinula. 



III. Parietal lamella simple; no angle lamella; parietals normal or increased 

 by accessory denticles, often standing on a callous ridge . . Vertigopsis, 



KEY TO THE SPECIES OF BIFIDARIA. 



I. Base of shell between umbilicus and margin compressed, forming a keel. 



a. Shell cylindrical, apex obtuse, length more than 4§ mm armifera. 



aa. Shell sub-conical, length 3 mm : contracta, 



II. Base of shell rounded. 



a. Aperture multidentate, labial teeth on a ridge of callus, contracting 

 the aperture. 

 b. Shell obtusely conical, last whorl widest, parietal and inferior pal- 

 atal teeth straight tappaniana. 



* Adapted from Pilsbry, Proc. A. N. S. P., 1900, 593. 



