254 Lingual Dentition of Gceotis. 



common in BuUmnlus and Cylindrella, but without the upper median tri- 

 angular plate characteristic of the latter; both margins scarcely serrated 

 by the ends of the ribs. 



From our numerous observations on the jaws of Pidmo- 

 nata (see Ann. Lye. N. H. of N. Y., X, 165), we consider 

 this to be a form of ribbed jaw, the phite-like sections being 

 actually divided by delicate longitudinal ribs. It is to be 

 understood that the jaw is not in separate pieces, as in Or- 

 thalicus and Liguus (sec I1)id, p. 168). Our figure of the 

 jaw of Helix turhiniformis, Pfr. (Ibid, pi. ii, fig. 2), gives 

 the same type of jaw, though differing in form. That of 

 Succinea 9 appendiculata (Ibid, X, pi. ix, fig. 2) is still 

 nearer the jaw we are considering. 



The lingual membrane is entirely different from what we 

 had supposed from our interpretation of Shuttleworth's de- 

 scription. We recognize no resemblance to that of Zoniles 

 and Vitrina, but rather (in arrangement and shape of teeth 

 and position of cusp) to that figured by us of Ortlialicus 

 zebra and undatus (Amer. Jour, of Conch. 1870, pi. ix, 

 figs. 2, 6, 10, 12,) and Liguus fasciatus drawn by Leidy, 

 (Terr. Moll. U. S. II, 270). From these, however, it dif- 

 fers in the development of its cusp, which shares the trifid 

 character, and nearly resembles that of Helix muscarum 

 (Am. Jour. Conch. I. c. fig. 4). 



Lingual membrane long and broad, composed of numerous rows of 

 teeth arranged en chevron. Centrals very long, narrow, obtuse above, 

 incurved at sides, obtusely rounded and expanded at base near which is a 

 short, gouge-shaped, expanded cusp, whose lower edge is bluntly triden- 

 tate. Laterals same as centrals in shape, but a little larger, and unsym- 

 metrical from the disproportionate expansion of the outer denticle of the 

 cusp. Marginals same as laterals, but more slender, with more developed 

 and graceful teeth, of which the median is pointed, often bifld. There is 

 much variety in the shape and deuticulation of the cusps. The middle 

 denticle is always the smallest. 



We 6nd no distinct marginal teeth of the aculeate type 

 noticed by Shuttle worth, but believe he was misled by see- 

 ing these teeth in exact profile, when they have somewhat 

 that form as shown in our figure 6. Seen from above, 



