MOLLUSCA OF MICHIGAN— WALKER. 469 



Helix thyroidus, Sager, Doc. H. Rep. Mich., 1839, 420, separate, 14. 



thyroides, Miles, Rep. Geol. Surv. Mich., 236, (1861). 



Mesodon , Currier, Shell-bearino- Moll. Mich., 5, (1868). 



, DeCamp, Shell-bearing Moll. Mich., 6, (1881). 



Polygyra , Walker, Rev. Moll. Fauna Mich., 16, (1894). 



Var. PULCHELLA Cockerell. 



Helix thyroides pulchella, Cockerell, Jour. Con., VII., 39, (1892). 



Pale horn-color, tinged with vinous, especially near the aperture. 



Generally distributed through the southern part of the state and on the 

 western side ranges as far north as Chippewa county. The variety occurs 

 not unfrequently in Kent county. 



POLYGYRA CLAUSA (Say). 



Shell sub-imperforate, conoidly semi-globose, rather solid 

 with crowded rib-like striae; yellowish horn-color, shining; whorls 

 5^, rather convex, gradually increasing, the last rounded, con- 

 Fig '>oT^sa stricted behind the lip ; umbilicus narrow, almost covered by the 

 '(Binney.) reflected peristome; aperture rounded; peristome narrow, white, 

 reflected; base very convex. 



Alt. 11^, greater diam. 18^, lesser 16 mm. 



Helix clausa. Say, Jour. A. N. S. P., II., 154, (1821). 



Mesodon clausus,W. G. Binney, Man. Am. Land Shells, 315, fig. 338, (1885). 



Helix clausa. Sager, Doc. H., Rep. Mich., 1839, 420, separate, 14. 



'-, Miles, Rep. Geol. Surv. Mich., 235, (1861). 



Polygyra , Walker, Rev. Moll. Fauna Mich., 16, (1894). 



Very rare in Michigan. Until recently Grand Rapids was the only authen- 

 tic locality recorded. But it has been lately collected in considerable 

 .abundance near Monroe. 



POLYGYRA niTCHELLIANA (Lea). 



Shell imperforate, depressed conoid-globose, thin; finely 

 striate; yellowish horn-color, polished; spire briefly conoid; 

 whorls 5, moderately convex, gradually increasing, the last 

 ventricose, sub-constricted behind the lip; aperture rounded, 

 Yig. 21. p. mitcheiiianaP^^^^^^^^ uarrow, white, thickened, reflected; base -very 



(Binney) COUVeX. 



Alt. 10, greater diam. 16^, lesser 14J mm. 



Helix mitchelliana, Lea, Trans. A. P. S., VL, 87, pi. XXIII, fig. 71, (1839). 

 Mesodon mitchellianiis , W. G. Binney, Man. Am. Land Shells, 305, fig. 326, 



(1885). 

 Polygyra mitchelliana, Walker, Rev. Moll. Fauna Mich., 16, (1894). 



Very rare; Armada, Macomb county, is the only reported localit}^ This 

 species in general appearance is very similar to P. clausa, but is distinguished 

 by being imperforate. 



