NATURAL SCIENCES OF PHILADELPHIA. 179 
tinct cutting points upon these cusps. Such cusps and points are 
present in solitaria (pl. VII., fig. 9), aléernata (fig. 5), perspectiva 
(fig. 3), striatella (fig. 10), Hemphilla (fig. 6), Idahoensis (fig. 4), 
asteriscus (pl. X VIIL., fig. 9). 
I do not detect these cusps in P. strigosa (pl. VII., fig. 1), 
Cooperi (fig. 2), probably the same species, or Cumberlandiana, 
excepting on the outer laterals (see pl. VII., fig. 1 d). 
The central and lateral teeth of all the species examined by me 
are, in other respects, as usual in the Helicine. 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 by 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. They 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 (pl. 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. 
