512 



MICHIGAN SURVEY, 1905. 



Fig. 135. B. penfcdon. (P. & V.) 



13. 



Not abundant, but apparently of general distribution through the state. 

 Closely related to B. tappaniana, from^which it is distinguished by its smaller 

 size, more cylindrical outline, and curved parietal and inferior palatal folds. 

 This species has been commonly known as B. curvidens Gld., But Dr. 

 Pilsbry has recently shown that this is the B. pentodon of Say and not the 

 species usually so called. 



BIFIDARIA TAPPANIANA (C. B. Adams). 



Fig. 136. B. tappaniana. (P. & V.) xl3.S. 



Shell sub-perforate, elongate, ovate, of a spermaceti or whitish horn- 

 color; w^horls 5, well rounded and separated by a deep suture; apex rather 

 acute; aperture oblique, nearly semi-circular; peristome sharp and some 

 what expanded, but not reflected; the inner margin thickened by a ridge 

 of white callus, on which the palatals are situated: lamellae 5 to 10, of which 



