u$ 



LAND AND FRESH-WATER SHELLS OF N. A. [PART 1. 



pearleaceous within ; peristome white, thickened, its terminations slightly 

 converging, subequally reflected, that of the columella 

 narrow, adherent, or subdilated and spreading. Greater 

 diam. IQh, lesser 14^ ; height 10 mill. 



240. 



Helix 

 tnitchelliana. 



Helix mitchelliana, Lea, Am. Phil. Trans. VI, 87, pi. xxiii, 



f. 71 ; Obs. II, 87 (1839) ; Troschel, Arch. f. Nat. 



1839, II, 221. — DeKay, N. Y. Moll. 45 (1843).— 



Pfeiffer, Mon. Hel. Viv. I, 291 ; IV, 322.— Bi,and, 



Ann. N. Y. Lye. VI, 339 (1858).— W. G. Binxey, 



Terr. Moll. IV, 47. 



Helix clausa, Bikney, Terr. Moll. II, 109 ; in Vol. Ill, pi. iv, outline figs. 



Mesodon mitchelliana, Tryon, Am. Journ. Couch. Ill, 45, pi. viii, f. 10 



(1867). 



Kentucky and Ohio. 



Jaw arcuate, of uniform widtii throughout ; ends blunt ; 

 anterior surface with crowded, coarse ribs, deuticu- 

 lating either margin. 



Lingual membrane with 136 rows of 42 — 1 — 42 

 teeth each; centrals long, stout, with a long, conical, 

 pointed apex ; laterals of same shape, but with an 

 obsolete side-cusp ; uncini bidentate, the inner den- 

 ticle very long, outer uncini with subequal denticles. 



Fig. 241. 



Jaw of Helix 

 mitchelliana. 



Fig. 242. 



Lingual deutitioD of Helix mitchelliana. 



Helix elevata, Say. — Shell imperforate, very convex, elevated, 

 almost conical ; epidermis yellowish horn-color ; whirls nearly seven, 

 rounded, with fine oblique transverse striae, the last ventricose ; suture 

 distinct : aperture contracted by the peristome, somewhat triangular ; 

 peristome white, thir-kened, reflected, its basal portion with an obsolete, 

 lamellar denticle ; parietal wall with a large, white, robust, obliquely- 



