56 PROCEEDINGS OP THE ACADEMY OP 



centrals, but unsymmetrical. Marginals quadrate, with one broad, 

 oblique, long, bluntly bifid inner cusp, and one or ^wo very short 

 rounded side cusps. 



Theiidomus. — We have examined H. asjoera, Fer. (Am. Journ. 

 Conch., YI. 204) ; discolor, Fer. (ante, p. 51) ; notabilis, Shuttl. 

 (Amer. Journ. Conch., VII. 177); Zma, Fer. (ante, p. 51); and 

 provisoria, Pfr. (Ann. Lye. N. Y., x. 347). 



There are 8 decided stout ribs on the jaw of aspera, 7 on that 

 of discolor and liyna, on provisoria we find 10-15 ribs, less decided 

 than in the other two species. 



I figure the lingual dentition of H. discolor (plate X., fig. 1). 

 H. aspera agrees with it. The marginal teeth of jjrovisoi'ia and 

 notabilis agree with those of aspera and discolor, but as the centrals 

 and laterals differ in the shape of the plates and the development 

 of the cusps, I also figure the central and lateral of notabilis 

 (plate IX., fig. 10), with which provisor-ia agrees. 



Cysticopsis we know by tumida, Pfr., and pemphigodes, Pfr. 

 For description and figure of the former see Ann. N. Y. hyc. 

 N. H., IX. 213, f. 3 ; Am. Journ. Conch., YI. 203, f. 1. Finding the 

 dentition of pemphigodes to be diflferent (Am. Journ. Conch., YII. 

 177) I here figure it (plate IX., fig. 1). 



Plagiojjtycha. — We have published ^. Zoa;o(7ow, Pfr., Albersiana, 

 Pfr., monodonta, Lea, diaphana. Lea, and macroglossa. (See Am. 

 Journ. Conch., YII. 177, 178.) The3' all agree in having a ribless 

 jaw with blunt median projection to cutting edge, and in dentition 

 such as I figure for H. macroglossa, Pfr. (plate X., fig. 10). 



Polymita — We have elsewiiere (Ann. N. Y. Lye, x. 341) pointed 

 out the necessity of revising this subgenus. The typical species 

 muscarum, and H. picta which must be removed to it from Lio- 

 chila, have a ribless jaw without median projection to the cutting 

 margin (see Am. Journ. Conch., YI. 204, pi. IX., f. 4, 10). The 

 lingual dentition of both species agrees (see ibid, and Ann. N. Y. 

 Lye, X. pi. xvi. fig. 14). It is entirely difl'erent from that of any 

 species now known. 



Hemitrochus must be used as the name for the balance of the 

 subgenus Polymita of von Martens. We have examined varians, 

 Mke. (Amer. Journ. Conch., YII. 206, and L. and Fr. w. Shells, I. 

 185) ; Troscheli, Pfr. (Ann. X. Y. L3'c., x. 343); graminicola, Ad. 

 (Am. Journ. Conch., YII. 178) ; galloiMvonis, Yal. 343. (N. Y. Am. 

 X. 343.) All agree in having an arched ribless jaw with blunt 



