Helix Jamaicensis, etc. 147 



Martens (1. c, 146) has as the type of Polymita. We as- 

 signed both muscarum and picta to Polymita, proposing that 

 other species, the dentition of which we had examined, em- 

 braced in that subgenus by v. Martens, should form a dis- 

 tinct group under the name of Hemitrochus, Swainson. 



We expressed the opinion that the curious lingual denti- 

 tion of H. picta might be found in H. sulphurosa, but not 

 in //. Jamaicensis, adding "the latter, which is the type of 

 Liochila, will therefore remain undisturbed in its systematic 

 position, unless indeed, it belongs to Thelidomus, in which 

 case the name Liochila will be placed in the synonymy of 

 the last named subgenus." 



Through the kindness of Mr. V. P. Parkhurst, who lately 

 visited Jamaica, I am enabled to solve the doubt as to the 

 subgeneric position of II. Jamaicensis. He brought from 

 that Island, and placed at my disposal, one living and two 

 dead specimens (in alcohol) of the species in question. I 

 am indebted to W. G. Binuey for the following description 

 of the jaw and dentition : — 



II. Jamaicensis has a jaw high, slightly arcuate, ends attenuated; no 

 median projection to cutting edge; anterior surface with 13 decided ribs, 

 varying in size and irregularly disposed, but denticulating either margin. 



Lingual nlenibrane long and narrow; teeth about 41-1-41, of the usual 

 Helicince type. Centrals with the base of attachment longer than wide, 

 and lower lateral angles greatly developed ; side cusps subobsolete, side 

 cutting points absent, median cusp stout, reaching only half way to the 

 lower edge of the base of attachment, beyond which projects slightly the 

 cutting point, whose outer lower sides are somewhat bulging. Laterals 

 same as centrals, but unsymmetrical as usual, and very gradually changing 

 into the marginals. The latter are a simple modification of the laterals, 

 with a very short, blunt, broad, bluntly bifid cutting point. 



Comparing the forms of jaw and lingual teeth with those, 

 especially of H. aspera (Amer. Jour, of Conch., VI, 204, 

 1870) and H. discolor (Proc. Phila. Acad. Nat. Sci., 51, pi. 

 x, fig. 1, 1874), belonging to Thelidomus, there can be no 

 doubt as to the correctness of placing H. Jamaicensis in that 

 subgenus. 



