486 



MICHIGAN SURVEY, 1905. 



Generally distributed in the northern part of the state. 

 The only locality reported south of Lake county is Grand 

 Rapids. Distinguished from Pyramidula asteriscus, the only 

 species with which it is likely to be confounded, by its 

 larger size and the position of the ribs, which are oblique to 

 the lines of growth. 



Fig. 62. Sculpture of 

 Z. exigua. (Binney.) 



ZONITOiDES niLIUM (Morse). 



Shell widely umbilicated, depressed, transparent, shining, 

 greenish- white, distinctly and regularly striate above, with 

 microscopic revolving lines, more conspicuous below; spire 

 very low; whorls 3, rounded, rapidly increasing; aperture very 

 oblique, semi-circular, remote from the axis; peristome simple, 

 acute. 

 Fig. 63. z. milium, ^^^t' i^ S^^^ter diam. H mm. 



XI Of. (Bmney.) 



Helix milium, Morse, Proc. B. S. N. H., VII., 28, (1859). 



Zonites , W. G. Binney, Man. Am. Land Shells, 66, fig. 23. (1885). 



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



Owing to its minuteness this species is apparently rare, but evidently has 

 a general distribution throughout the state. "The surface of the shell is 

 raised in numerous costal folds, frequently anastomosing; longitudinal ribs 

 reticulate the surface and render the folds so crenulated that in certain 

 lights the shell appears as if ornamented with strings of beads. This pe- 

 culiar character disappears at the base of the shell and is replaced by re- 

 volving lines and regular lines of accretion." — (Morse). 



Genus QASTRODONTA Albers. 



Shell subperf orate or umbilicated, orbicularly convex or depressed, light 

 horn-color, finely and obliquely striate, sometimes glassy; whorls 5-7, aper- 

 ture lunate, base furnished with internal teeth, not reaching the margin, or 

 thickened by an internal deposit of callus; peristome simple acute. - 



Animal bluish-black or dark slate-color above, paler on the posterior ex- 

 tremity and base; foot narrow and long; eye-peduncles long and slender; a 

 distinct locomotive disk; pedal grooves terminating in a longitudinal mucus 

 pore. 



Fig. 64. 



Animal of G. ligera. 



(Binney.) 



F'sr. 65. 



Tail of G. suppressa. 



(Binney.) 



Fig. 66. 

 Jaw of G. ligera. 



Jaw strongly arcuate, ends rounded; anterior surface striated; concave 

 margin with a well developed median projection. 



