MOLLUSCA OF MICHIGAN— WALKER. 483 



Genus ZONITOIDES Lehman. 



Shell depressed or subdiscoidal, umbilicate, smooth or ribbed, striate or 

 costulate, shining, pellucid, corneus, aperture obliquely 

 lunate. No internal teeth or callus. 



Jaw long, narrow, arcuate with ends pointed or 

 ^. _ , . r. . rounded, lower margin smooth, with a wide median 



Fig.55. Jaw of Z. or&crea. • • t\ i-j^- a • ,^ i- ^^ 



(Binney.) impressiou. Dentitiou as usual ni the family. 



Fig. 56. Dentition of Z. nrb^.j-ea. — (B.nnej-.) 



Section ZONITOIDES s. s. 

 Surface polished. 



KEY TO THE SPECIES OF ZONITOIDES. s.s. 



I. Umbilicus wide, diameter 7^ mm nitida. 



II. Umbilicus moderate, diameter 5 mm. arhorea. 



ZONITOIDES NITIDA (MuUer). 



Shell widely umbilicate, depressed, moderately convex above 

 and concave below, thin, shining, uniform yellowish horn-color; 

 delicately striate; whorls 5 or more, convex; suture impressed; 

 outer whorl large and obtusely angular at the periphery; aper- 

 ture oblique, lunate, rounded below; peristome simple. 



Alt. 3f , greater diam. 7^, lesser 6 mm. 



Z. nitida (Binney.) 



Helix nitida, Muller, Hist. Verm., II., 32, (1774). 



Zonites nitidus, W. G. Binney, Man. Am. Land Shells, 60, fig. 12, (1885). 



Helix hydrophila, Miles, Rep. GeoL. Surv. Mich., 235, (1861). 



Hyalina nitida, Currier, Shell-bearing Moll. Mich., 4, (1868). 



, DeCamp, Shell-bearing Moll. Mich., 5, (1881). 



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



A common and abundant species of general distribution. It frequents the 

 muddy banks of streams, where it is associated with the Succineas, Pomati- 

 opsis and other semi-amphibious species. When alive, it is easily identified, 

 not only by its greater size, but by the dark color of the animal which makes 

 the shell appear to be black, when cleaned it is distinguished from Z. arhorea 

 on the one hand by its greater size and wider umbilicus and from V. cellaria, 

 on the other, by its more convex whorls and lack of the basal callus-deposit. 

 46 



Fig. 57. 



