252 



A MANUAL OF AMERICAN h.\Sh SHELLS. 



name diodonta, preoccupied in Helix, has precedence as a Mesodon. I 

 have, however, thought it best to retain the well-established specific 

 name in all cases, to avoid future confusion. 



The external generic characters of the animal of the various groups 

 now recognized as genera do not differ. 1 reier, therefore, for them to 

 Patula, the first genus of dismembered Helix included in this portion 

 of my work. 



PATULA, Hald. 



Animal heliciform; body elongated, semi cylindrical, tapering to a, 

 ^^«- 263- point posteriorly, convex above, 



plane beneath ; mantle simple, 

 central, not extending beyond 

 and accurately fitting to the 

 peristome of the shell, into which 

 the whole animal may retire; 

 Animal of Patula soiitaria. liead obtusc J cycs at the cud of 



long, cylindrical, retractile, peduncles; tentacles short, retractile; 

 generative orifice on the side of the head, behind the right eye-pe- 

 duncle ; respiratory orifice in the collar, at the angle of the aperture of 

 the shell; anal orifice immediately adjoining; no caudal mucus pore, 

 no locomotive disk. 



Shell widely umbilicated, depressed, discoidal, turbinate, rugose, or 

 costulately striate ; whorls 4-6, equal or gradually increasing ; aper- 

 ture lunately rounded ; peristome simple, straight, acute. 



As there appears considerable confusion in regard to the limits of 

 the genus, I think it best to make no reference to any species foreign 

 to North America. Here it ranges over both the Central and Eastern 

 Provinces. 



In none of the American species of this genus have I found a jaw 

 with distiuct, well-formed, ribs as in Helix. In several species, how- 



FlG. 2C4. 



Fig. 265. 



Jaw o{ Patula antcriscus. (Morse.) 



Patula striatclla. (Morse. J 



ever, such as strigosa and Cooperi (see ante, p. 106), there are distinct! 

 traces of subobsolete ribs near the cutting margin ; in asterisciisihere' 

 are coarse wrinkles, resembling subobsolete ribs; in jyerspectiva, stria- 

 tella, and Idahoensis there are such wrinkles, and also coarse vertical 



