342 



a rule, the ribs on the outer volution are not more developed than on the 

 Canadian specimen No. 14." 



Pachydiscus Neevesii. (N. Sp.) 



Plate 47, fig. 1. 

 Shell compressed convex and rather narrowly umbilicated, volutions 

 somewhat closely convolute, a little more than half of the inner ones being 



FiQ. 21. — PachydAscus Neevesii. Outline of transverse section of the outer volution, near 

 the aperture, of the specimen from James Island represented on Plate 47. 



covered by those that succeed them ; umbilicus occupying one-fourth of 

 the entire diameter, its margin rounded and its inner wall rather steep. 

 Aperture higher than wide, broadly subelliptical, but rather deeply 

 emarginate by the encroachment of the preceding volution. 



Surface of the outer volution marked with numerous, very slightly 

 elevated, gently flexuous, transverse ribs, which are everywhere much 

 narrower than the very shallowly concave or nearly flat spaces between 

 them. On the periphery and near the aperture of the specimen figured 

 the ribs average from two to three millimetres in breadth, and from 



