14 



rangement of the plates, it differs in a marked degree by the 

 hydrospires being single, and not paired, as is the case in C. jcw- 

 ettii, Apiocysfifrs eh\i:;a)is, and alli(^d species ; and while I am in- 

 clined to think it may be of generic importance, the question 

 cannot be decided until other material is found for more critical 

 determination. 



PLATYCERAS LACINIOSUM (N. Sp.). PI. 2, fig. r. 



Shell involute, slightly compressed laterally, coiled nearly on a 

 plane, forming a little more than one volution, which is free 

 throughout its entire extent, and regularly increasing in size to- 

 wards the aperture ; outer side of volution flattened and sepa- 

 rated from the sides by two sharp, lateral carina ; the ventral one 

 of which loses its sharpness as it approaches the aperture, where 

 its position only is designated by slight undulation in the reflexed 

 striae ; this flattened space projects sharply beyond the aperture, 

 as far as the width of the flattened portion; it bears upon its sur- 

 face, somewhat to its upper side, a rather wide, well defined prom- 

 inent ridge; inner side of volution evenly rounded; ventral side 

 convex ; upper side convex towards the inner side and concave 

 towards the outer ; aperture curved backwards next to the lateral 

 carinae, the curvature being broadest and extending further in- 

 wards on the upper, and narrower and more sharply defined on 

 the ventral side. Concentric striae fine, and closely arranged. 



This species is readily distinguished from P. angiilatiiin, with 

 which it is associated, .by its being coiled nearly on a plane, in- 

 stead of having the spire directed towards the upper side, its 

 laterally compressed form, and by having the angulate portion 

 sharply defined, and projecting further beyond the aperture. 



PLATYCERAS PROCLIVE (N. Sp.). PL 2, fig. 2. 



Shell dome-shaped, patelliform and low. Apex obtuse, sub- 

 anterior, inclined posteriorly and a little to one side, and but 

 slightly elevated above the surface. Aperture oval, twice as wide 

 in its longest diameter as the height of the shell. Surface marked 

 by regular concentric striae, that are crossed by well defined 



