222 PROCEEDINGS OF THE ACADEMY OF 



of attachment and bearing one inner, long, oblique, acutely bifid 

 cutting point, and one shorter, outer, sometimes bifid, side cutting 



point. 



The only other Pomatia whose dentition has been figured is 

 H. pomatia, which shows the same type of teeth (Goldfuss, 1. c. 

 pi. IV., fig. 6). The jaw of numerous European species is known, 

 and of the same type as in aspersa. 



(3) Jaw with delicate, distant ribs to its anterior surface, usually running 

 obliquely to the median line. 



Genus CYLINDRELLA, Pfr. 

 Jaw as in 31acroceramus, described below. 

 Lingual membrane of our two species C. jejuna and G. Poeyana 

 not examined b}' me. The dentition of the genus is very peculiar. 

 The membrane is exceedingly long and narrow. The base of 

 attachment of the centrals is small, long, narrow, with the upper 

 margin broadly reflected into a blunt, rounded and expanded 

 gouge-shaped cutting point ; the laterals have a long, subquad- 

 rangular base of attachment, bearing below, a large, bluntly 

 rounded, greatly expanded, palmate cusp, representing the inner 

 and central cusps of the laterals ; and, above, a long, slender, graceful 

 extension, representing the external cusp of the other Helicidse. 

 This last is bluntly truncated, or bears a recurved cusp smaller 

 but of same shape as that below ; or it has a laterally extended, small 



blunt point. In some species the laterals 

 '" extend to the margin of the lingual mem- 

 brane j 1 in others there are distinct marginal 

 teeth, long, narrow, laminar, with bluntly 

 recurved apices. A full description and 

 figures of these various forms of teeth will 

 be found in Journal de Conchyliologie, 

 January, 1870. 



I here give a figure of the dentition of one 



Lingual uVutitiun of , , 



r.tiindreiiascava. [Biand.] onl J of these types represented by the 



membrane of C. scseva. 



1 Probably this is the case in our species, as it is so in the allied C. clegans. 

 See pi. XX., fig. 6. 



Since the above was written, I find my anticipations realized in the case 

 of C. Poeyana. Specimens from Key West collected by Mr. W. W. Cal- 

 kins, have 14114 teeth of same type as in elegans. There are over 40 

 ribs on the jaw. m 



