Dentition of Pulmonata. 36 



liquely toAvards the median line, so that those of the centre converge 

 before reaching the bottom of the plate. These ribs serrate the upper 

 and lower margins. They increase in thickness gradually on their outer 

 edge. There are twenty- one ribs on the specimen examined. The ma- 

 terial of the jaw is so thin on the outer edge of the ribs irhat it separates 

 into distinct plates at these points, when macerated. In some specimens 

 examined the ribs appear to be formed by an actual overlapping of distinct 

 plates. I have no doubt, however, of the jaw being in one single piece, 

 divided by these delicate ribs into numerous plate-like compartments. It 

 is not composite as formerly believed by most authors. 



The lingual membrane (pi. I, fig. 1) is broad, very delicate in texture and 

 difficult to handle. There are numerous rows of about 90-1-90 teeth each. 

 The centrals have a base of attachment longer than wide, with lower lat- 

 eral expansions. The reflection has one stout median cusp, the side cusps 

 being obsolete ; this cusp bears a short, rapidly attenuated, sharp cutting 

 point, not reaching the lower margin of the .base of attachment. The lat- 

 erals are of same type as centrals, but unsymmetrical, the cutting point, 

 however, is very difl"ereut from that of the centrals, being very broad, 

 bluntly rounded at its end, oblique, extending far below the base of at- 

 tachment, and having on its inner margin, near the blunt end, a promi- 

 nent blunt notch. The marginals are a modification of the laterals, but 

 lower, with a much more oblique cusp, bearing a much broader trifid 

 cutting point, the middle division very much more produced than the outer 

 ones. 



The figures represent a one central with its adjacent lateral teeth, and 

 h, two marginal teeth. 



The lateral teeth are a modification of the usual Helicidce type not before 

 observed by me. The marginal teeth are somewhat like those seen in 

 many species of Bulimulus, such as laticinctus, Bahamensis, auris-leporis, 

 papyraceus, Jonasi, membranaceus. They only approach, however, the 

 teeth of those species in form. 



Bulimulus rhodolarynx, Eve. (^Scutalus.) 

 Northern Peru. Prof. Orton. 



The genital organs were so reduced as to be only threadlike, and not 

 sufficiently developed to be described as perfect. 



The jaw was not examined, being of so delicate texture as to be quite 

 destroyed by the action of potash. 



The lingual membrane is long, narrow. Teeth about 40-1-40, of the 

 usual type of Helicince (see pi. I, fig. v). The central teeth, a, have one 

 median cusp, the outer cusps being obsolete, the cutting point is short 

 and bluntly pointed. Lateral teeth same as centrals, unsymmetrical, the 

 inner subobsolete cusp more developed. The marginals (b) are simple 

 modifications of the laterals, subquadrate, bicuspid, each cusp with a 

 long, oblique, stout cutting point. 



