170 PROCEEDINGS OF THE ACADEMY OF 
attachment, beyond which projects slightly the distinct, long 
cutting point. lLaterals like the centrals, but unsymmetrical by 
the suppression of the inner, lower angle of the base of attach- 
ment, and inner side cusp and cutting point. Marginals (C) acule- 
ate, their bases of attachment less sole-like than in Zonites, but 
more circular in outline. © 
Fig. 10, C, shows these bases of attachment. ne 10, D, gives 
one arena tooth in profile. 
This is the first known instance of a species with ribs on its 
jaw having aculeate marginal teeth, or of a species furnished with 
a Zonites-like shell having decided ribs upon the jaw. It will be 
difficult to find a place for the species under any description of 
genus or subfamily. The shell is that of Zonztes, but that genus 
has a ribless jaw with median projection. 
Fig. 11. Fig. 13. 
mre 
Jaw of Z. arboreus. [Morse.] Jaw of Z. fuliginosus. Jaw of Z. indentatus. [Morse | 
The jaw of Zonites is arcuate, ends acuminated, often recurved ; 
anterior surface without ribs; cutting margin with a beak-like 
projection. 
I have examined the jaws of almost all the species enumerated 
above. There is considerable variation in their form, but the 
general characters are constant. 
IDs ee Sometimes there is a vertical me- | 
See ie dian carina, as in Z. minusculus. 
Some species have vertical striae, 
especially on the middle of the 
jaw (see fig. 14). Some have strong 
transverse lines of reinforcement 
(see fig. 12). In several species, 
such as Z. viridulus and Z. Bin- 
neyanus (fig. 14), Morse has detected projecting points on the 
cutting edge of the side of the median beak. But I did not find 
them in a specimen of the last species examined by me; it is very 
high. That of Z. exiguus is very low. The median vertical 
erooves in some species have been mentioned above (fig. 7 and 8). 
Formerly I separated the above species into two genera, 
Jaw of Z. Binneyanus. [Morse.] 
