116 Dentition of Pulmonate Mollusk's. 



found in Cylindrella ; no upper median ribs en chevron, but all the ribs slightly 

 oblique. 



Lingual membrane (PI. XI, fig. F); centrals tricuspid, laterals bicuspid, 

 each cusp with long cutting point. 



(c) Jaw with separate, delicate ribs, usually running 



OBLIQUELY TOWARDS THE CENTRE, 



Several species are found in the last genus with this type of 

 jaw. 



Gaeotis. 



The genus Gceotis was described by Shuttleworth,* founded 

 on a curious mollusk from Porto Rico. The lingual dentition 

 was said by him to be nearly the same as in Vitrina and Zonites, 

 the teeth arranged in oblique rows, centrals obtusely tridentate, 

 laterals scarcely differing from the centrals, marginals length- 

 ened, awl-shaped, arcuate, at base ? bifurcate. The presence of 

 a jaw was not verified by Shuttleworth. The character of the 

 dentition was considered such as to denote carnivorous habits of 

 the animal. 



An examination of an unidentified Porto Rico specimen (Mr. 

 R. Swift) has furnished the following description. 



GcboUs . 



Jaw (PI. XV, fig. A) long, low, slightly arcuate, ends attenuated, ex- 

 tremely thin and delicate, transparent; in one single piece, but divided by 

 over fortyf delicate ribs into as many plate-like compartments of the type - 

 common in Cylindrella and Bulimulus, but with no upper median triangular 

 space ; the ends of the ribs serrate the upper and lower margins. 



Lingual membrane (PI. XI, figs. H, I) long and broad, composed of nu- 

 merous rows of teeth arranged en chevron. Centrals with base of attachment 

 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 has three bluntly-rounded cutting points. Laterals same 

 as centrals in shape, but a little larger, and asymmetrical from the dis- 

 proportionate expansion of the cutting point. Marginals same as laterals, 

 but more slender, with more developed and graceful cutting points, of 



* Ferussac's figure of Parmacella palliolum seems to show a jaw with stout 

 ribs; I do not think Gceolls can belong to the same genus, Peltella. 



f Fragments only of the jaw were saved ; the largest one I have 

 figured, and from it estimate the whole number of ribs. 



