MESODON. 339 



CXCIII. Fig. 12. KEEVE, Con. Icon., 682. W. G. BINNEY, Terr. Moll., 



IV. 70 ; L. & Fr.-W. Sh., I. 152 (1869). 

 Helix Richardi, FERUSSAC, Tab. Syst. 43 ; Hist., PI. LXX. three lower figs. 



LAMARCK, An. s. Vert., VI. 72. DESHAYES, Encycl. Meth., II. 212; in Lam., 



VIII. 40; ed. 3, III. 283. CHENU, 111. Conch., PL XII. Fig. 13. DELES- 



SERT, llec. des Coq., PI. XXVI. Fig. 7. 

 Junior? Helix bulbina, DESHAYES in FER. Hist., I. 108, PI. LXXXV. Figs. 



14_18._ PFEIFFER, Mon. Hel. Viv., III. 201. W. G. BINNEY, Terr. Moll., 



IV. 116, PI. LXXIX. Fig. 10. 

 Ulostoma profunda, TRYON, Am. Journ. Conch., III. 37 (1867). 



A Post-pleiocene species, now found in the Interior Region ; from Western 

 New York to Minnesota, Virginia to Kansas. 



Animal light brown, darker on the head, neck, eye-peduncles, and tentacles, 

 and pale on the posterior extremity ; foot rather thick, in length less than 

 twice the diameter of the shell, terminating acutely. (See Bost. Journ. Nat. 

 Hist., I. PL XV.) 



Jaw arcuate, of uniform width, ends blunt; anterior surface crowded with 10 

 stout ribs, denticulating either margin. 



The lingual membrane (PL VIII. Fig. Q) has 40 1 40 teeth, with about 

 14 perfect laterals, but the change from laterals to marginals is very gradual, 

 being made without splitting of the inner cutting point, which is simple on the 

 extreme marginals even. 



Genitalia figured by Leidy (1. c.). The penis sac is not very stout, long, 

 receiving the retractor muscle at about the middle of its length, and tapering 

 very gradually towards its summit into the vas deferens; genital bladder large, 

 globose-oval, on a long, narrow duct. The penis sac is very different from 

 that of M. Sayii. 



Mesodon Sayii, BiNNEY. 1 



Vol. III. PI. XXIII. 



Shell umbilicated, orbicularly depressed, thin ; epidermis light russet, shin- 

 ing; whorls between 5 and 6, with numerous fine, oblique striae; suture im- 

 pressed ; aperture lunately subcircular, not dilated ; peristome white, narrow, 

 thickened, reflected, with a slightly projecting tooth on the inner edge of the 

 basal portion near the umbilicus ; parietal wall with a sub-prominent, white 

 tooth ; umbilicus open, deep, not wide, exhibiting all the volutions, slightly 

 contracted by the reflected peristome ; base rounded, with the striae distinct, 

 converging into the umbilicus. Greater diameter 2 7, 2 lesser 23 mill.; height, 

 17 mill. 



1 The name diodonta, which has not precedence in the genus Helix, may be adopted in 

 Mesodon by those who follow the strict laws of nomenclature ; I doubt myself the pro- 

 priety of changing the long-established name in any of the genera formed from disinte- 

 grated Helix. 



2 One specimen measured 41 mill. 



