226 



LAND AND FRESH- WATER SHELLS OF N. A. [VART I. 



Fig. 384. 



pointed, vertical striae very fine, scarcely any denticles on the 



concave margin. Morse describes 

 the jaw of specimens from Maine 

 as slightly arcuate, tapering to a 

 point laterally ; anterior surface 

 with conspicuous longitudinal 

 striae : the middle of the concave 



Jaw of Cionella sttbcylindrica. [Morse.] 



margin produced into an obtuse beak. 



On p. 224 I have given a figure of the lingual membrane of a 

 Maine specimen. There are 90 rows of 43 teeth (21 — 1 — 21) ; 

 central plate long, very narrow, with a minute central tooth, with 

 traces of' a denticle at each side of its base ; laterals square, 

 bicuspid, first cusp wide and strong, as long as plate, second 

 cusp short, obtuse ; first seven uncini tridentate, inner denticle 

 prominent ; the rest short wide plates, denticulated, two extreme 

 uncini plain. 



Fig. 385 a gives an enlarged view of the central and first lateral 



Fig. 385. 



bJ 



Teeth of Cionella subcylindrica. [Moebe.] 



teeth of an American specimen, which may be compared with 

 the fac-siraile (Fig. 385 6) of the same, of Thomson (Annals Nat. 

 Hist. VII), from an English specimen. The differences between 

 the central teeth are certainly very great, but of what value in 

 determining specific distinction I am not prepared to say. 



