MOLLUSCA OF MICHIGAN— WALKER. 511 



in the throat; iimbihciis minutely perforate; base of shell sharply keeled 

 between the umbilicus and margin; last whorl impressed behind the peris- 

 tome. 



Alt. 3, diam. If mm. 

 Pupa contracta, Say, Jour. A. N. S. P., II., 374, (1822). 



, W. G. Binnev, Man. Am. Land Shells, 327, fig. 353*, 



(1885). 



, Miles, Rep. Geol. Surv. Mich., 236, (1881). 



Leucochilla , Currier, Shell-bearing Moll. Mich., (1868). 



. DeCamp, Shell-bearing Moll. Mich., 7, (1881). 



Pupa , Walker, Rev. Moll. Fauna Mich., 17, (1894). 



The most common species of the genus and of general distribution over 

 the entire state. 



Section PRIVATULA Sterki. 



Parietal and angle lamella^ very small, short and tuberculiform ; no palatal 

 folds; shell cjdindrical. 



BIFID ARIA CORTICARIA (Say). 



Shell whitish, shining, cylindrical, apex obtuse; whorls 5-6, con- 

 vex; suture well impressed; aperture two-thirds as wide as the last 

 whorl, sub-orbicular, with a single tooth (sometimes two) on the 

 parietal wall, near the centre and a tooth-like enlargement near 

 the umbilical termination of the peristome, which is white, re- 

 ,p ^24 fleeted; umbilicus very minutely perforated. 

 B.corticaria. Alt. 2^, diam. 1 mm. 



(Binney.) ''^ 



Odostomia corticaria, Say, Nich. Encycl. IV, pi. IV, fig. 5, (1817). 



Pupa , W. G. Binney, Man. Am. Land Shells, 330, fig. 355, 



(1885). 



Leucochilla , DeCamp, Shell-bearing Moll. Mich., 7, (1881). 



Pupa , Walker, Rev. Moll. Fauna Mich., 17, (1894). 



Apparently of general distribution over the entire state. Differs from all 

 the other species of the genus in the lack of labial teeth. 



Subgenus VERTIQOPSIS (Ckll.) Sterki. 



Parietal lamella simple; no angle lamella; palatals normal or increased by 

 accessory denticles, often standing on a callous ridge. 



BIFIDARIA PENTODON (Say). 



Shell ovate, sub-cylindrical, much elongated; spermaceti white; whorls 5, 

 convex, smooth, gradually diminishing to an obtuse apex; suture deeply 

 impressed; aperture sub-triangular, the transverse margin straight and 

 slightly oblique, columella nearly straight; peristome somewhat expanded, 

 thickened within by a callus deposit bearing the lamellae; lamellae five to 

 nine, the parietal and inferior palatal curved to the left; perforate. 



Alt. 1§ diam., | mm. 

 Vertigo pentodon, Say, Jour. A. N. S. P., II., 376, (1821). 

 Pupa curvidens, Gould, Invert. Mass., 189, fig. 120, (1841). 



pentodon, W. G. Binney, Man. Am. Land Shells, 323, fig. 347, 



(1885). 

 curvidens, Walker, Rev. Moll. Fauna Mich., 17, (1894). 



