JVbrth American Terrestrial Mollusks. 161 



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Cylindrella (p. 22). — In this genus there is a jaw, 



thin, almost membranous, light horn color, semitransparent, 

 arched, ends but little attenuated ; in one single piece, but 

 divided by delicate ribs into numerous oblique plates,* 

 chevroned on the central line, with a median triangular plate 

 at the top ; cutting edge simple ; no beak. 



The teeth are not joined two by two at their bases. They 

 are distinct as in the other Helicidm. The centrals are small, 

 long, narrow, with a broadly recurved, blunt, rounded and 

 expanded apex ; the laterals have a long, subquadrangular 

 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 cusp, representing the external cusp of the other 

 Helioidoi. This last is bluntly truncated, or bears a re- 

 curved 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 membrane ; 

 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, Jan., 1870. 



HoLOSPiRA (p. 24). — Messrs, Crosse and Fischer, in the 

 article on Cylindrellidoe, referred to above, hav^ shown that 

 Holospiixi is a distinct genus from Cylindrella. 



The jaw is arcuate, about the same shape as in Gylindrella, 

 thin, light horn colored, without separate plates or anterior 

 ribs; with obsolete striae, transversal and vertical; cutting 

 edge simple, without a median beak. 



The lingual membrane wants entirely the chevron-shaped 

 rows of teeth and the palmate form of cusp, characteristic of 

 Cylindrella. It resembles that usual in the Helicid(E, the 

 lateral teeth not unlike those we have figured of Bulimulus 

 pallidior (Ann. Lye. N. H. of N. Y., ix., p. 282)! 



* As in Helix turhirdformis, uot as in Orthalicus. (See Ann. N. Y. Lye, X., 79, pi. ii. 

 fig. 2.) 



