CERION, GROUP XIV. 277 



very finely, sharply striate, the latter four with coarser riblets, much 

 narrower than their intervals, about 30 in number on the penultimate 

 whorl. 



Aperture ovate, large and open, white, higher than wide. Per- 

 istome expanded and recurved, rather thick ; axial lamella basal ; 

 parietal lamella narrow, nearly a half whorl long ; an accessory in- 

 fraparietal lamella ascends around the root of the columella, but at 

 the apertural termination approaches close to the main parietal 

 lamella ; its termination visible in a front view. 



Length 29, diam. 10^, long axis of aperture 11^ mill. 



Bahamas, 



O. duplodon P. & V., Proc. A. N. S. Phila. 1896, p. 337, pi. 11, 

 f. 26. 



This is an albino form of the Diacerion group, differing from C. 

 rubicundum and its immediate allies in the greater distance between 

 the two parietal lamellas within, the more expanded aperture and 

 delicate riblets. 



XIV. Group of C. striatellum (Cuba). 



Paracerion P. & V., Proc. A. N. S., Phila., 1895, p. 206 (June 

 18) Tridentistrophia MAYNARD, Contrib. to Science, iii, p. 9 

 (March, 1896). 



The parietal lamella is long, extending inward to a dorsal position, 

 and usually interrupted or partially so in the middle, when it would 

 be described as two lamellae, one behind the other. A short infra- 

 parietal lamella lies between the middle of the parietal lamella and 

 the axis. Axial lamella and other characters as usual. 



This group is either an incipient or a degenerate stage of the 

 Diacerion branch ; and in the present state of our knowledge, I see 

 no means of deciding which. The armature of the parietal wall is 

 exactly paralleled by that of some degenerate forms of Diacerion 

 from Inagua. 



Three species are known : C. tridentatum, smooth, white with some 

 zigzag gray marbling, and the aspect of C. incanum ; C. striatellum, 

 very strong, densely rib-striate, with short mouth and thick peri- 

 stoine, and O. basistriatum, a nearly smooth and thin species other- 

 wise resembling striatellum. 



