NATURAL SCIENCES OF PHILADELPHIA. 179 



tinct cutting points upon these cusps. Such cusps and points are 

 present in Holitaria (pi. YII., fig. 9), alternata (fig. 5), pen^pectiim 

 (fig. 3), striatella (fig. 10), Hemphilli (fig. 6), Idahoensis (fig. 4), 

 asteriscus (pi. XVIII., fig. 9). 



I do not detect these cusps in P. strigosa (pi. VII., fig. 1), 

 Cooperi (fig. 2), probabl}' the same species, or Gumherlandiana, 

 excepting on the outer laterals (see pi. VII., fig. 1 d). 



The central and lateral teeth of all the species examined by me 

 are, in other respects, as usual in the HeMcinse. It will be noticed 

 that the base of attachment is subquadrate, the reflected portion 

 large (except in asteriscus), the cusps short, the cutting points 

 short. 



All the outlines of the teeth are less graceful than in Zonites. 

 The lateral teeth are made unsymmetrical b}' the suppression of 

 the inner lower angle of the base of attachment, and the less de- 

 velopment, if not suppression, of the inner cusp, which loses the 

 cutting point also. The marginal teeth are quite different from 

 those of Zonites, Limax, Vitrina, Macrocyclis, and Glandina in 

 not being aculeate. They are more crowded than in those genera. 

 They have a quadrate base of attachment, not sole-like, shortened 

 on its inner lower side, but produced at its outer lower margin. 

 The reflected portion is as wide as the base of attachment, is more 

 produced than in the central and lateral teeth, retains its width 

 throughout, and bears two oblique, blunt cutting points, the inner 

 one always much the larger and longer, and the outer one of 

 which, in most of the species, has a tendency to bifurcation. 

 There is considerable variation in these cutting points even in the 

 same lingual membrane, but as a general thing it may be said that 

 the marginal teeth are but a modification of the form of the 

 laterals. Thev decrease in size greatly at the outer edge of the 

 lingual membrane. 



It must be borne in mind that the cutting points vary in de- 

 velopment on different portions of any one lingual membrane. I 

 have in each case chosen for drawing such individual teeth as 

 appear best to illustrate the general character of the dentition. 



In P. strigosa (pi. VII., fig. 1) there are 50 — 1 — 50 teeth, with 

 15 perfect laterals, c is an extreme marginal. I give in fig. e a 

 central tooth drawn from the membrane of an embryonic young 

 found in the oviduct. 



