342 



GASTEROPODA. 



Pleurotomabia Canadensis. (N. sp.) 



Fig. 328. 



Fig. 328. — Pleurotomaria Cnnodensis. n, front view of a cast of the interior ; b, spire of 

 a specimen with the shell preserved with a wide smooth marginal band ; 

 c, a specimen with a sharp elevated margin, and with the surface reti- 

 culated by transverse and spiral lines. 



Descri])tion. — Shell large, lenticular ; spire varying from nearty flat to 

 depressed conical ; whorls about six, rather slender, a wide shallow con- 

 cave band just within the margin, the inner two thirds gently convex ; 

 suture distinct. The margin in some specimens is acute and turned 

 upwards ; in others with a rounded band sometimes one line in width. 

 Umbilicus wide, usually one-half or two-thirds the whole width, the mar- 

 gin sub-angular, and the slope of the whorls within flat or nearly so. The 

 under side of the whorls have usually a shght concave band just beneath 

 the margin ; thence to the edge of the umbilicus uniformly convex, often 

 strongly so. The aperture is transversely ovate or obscurely rhomboidal, 

 the outer and inner angles acute, the contour corresponding to the form 

 of the whorl. 



