342 Lingual Dentition and Anatomy of 



synonymy of the last named subgenus. Of the species re- 

 ferred to Polymita we presume none Avill prove to have 

 similar dentition unless, as may probably be the case, H. 

 verfiicolor, Born, so that the others must all be removed from 

 Polymita, to form a distinct subgenus under the name of 

 Hemitrochus, Swainson, 1840. We have, however, ourselves 

 examined oulj'- H. varians, Mke., Troschell, Pfr., gallopavo- 

 nia, Val., and graminicola, Adams, all of which have the 

 usual form of lingual teeth of the Helicldm (see Amer. Journ. 

 Conch., VI, 206^ VII, 178, and L. and F. W. Shells, N, A., 

 VI, 185, tig. 325). The jaw offers no subgeneric character 

 to distinguish the two subgenera Polymita and Hemitrochus. 



The long, subquadrangular lingual tooth, not reflected 

 along its upper margin as usual in the Helicidce, but bearing 

 the gouge-shaped, expanded, cutting edge, soldered as it were 

 upon its surface, has never been noticed by us before in the 

 genus Helix. It is, however, characteristic of Orthalicus* 

 of G<jeotis,-\ and of the marginal teeth of Liguus.X 



Our fig. 1, of pi. xvi, represents the jaw of H. picta. 

 Fig. 2 gives two central teeth of the lingual membrane with 

 the adjacent laterals. 



Helix g'a.lloi>sivOBia§, Val. (Hemitrochus). 



Jaw as ia Helix varians (see L. and F. W. Shells, I, p. 185, f. 325) aud 

 H. Troschell (herewith described). 



Lingual membrane as usual in the Helicidce. Cusps of centrals and 

 laterals stout, short, with short points ; side cusps subobsolete. The re- 

 flected cutting; portion of both centrals and laterals does not reach beyond 

 the middle of the plates, which are very long. Marginal teeth low, wide, 

 with four or more short, oblique, bluntly rounded denticles, the two 

 inner ones the largest. 



We are indebted for the specimen examined of this Turk's 

 Island species, and the following one from New Providence, 

 Bahamas, to Governor Rawson. 



* See Amer. Journ. Conch., VI, 212, 21.3, pi. ix, figs. 2, 10, 12. 

 t See Ann. N. Y. Lye. Nat. Hist., X, 2.52, pi. xi, figs. 5, 6, 7. 

 X See Amer. Journ. Couch., VI, 209, 211, figs. 4, 5. 



