170 



PROCEEDINGS OF THE ACADEMY OF 



attachment, bejond which projects slightly the distinct, long 

 cutting point. Laterals 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. Fig. 10, D, gives 

 one marginal tooth in profile. 



This is the first known instance of a species with ribs on its 

 jaw having aeuleate marginal teeth, or of a species furnished with 

 a Zonites-\\kQ 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 Zonites, but that genus 

 has a ribless jaw with median projection. 



Fig. 11. Fig. 12. Fig. 13. 



Jnw of Z. arboreus. [Morse.] Jnw of Z. fuliginosus. Javr of Z. hidenlatnx. [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 cliaracters are constant. 

 Fig. 14. Sometimes there is a vertical me- 



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. e.xiguus is very low. The median vertical 

 grooves in some species have been mentioned above (fig. 1 and 8). 

 Formerly I separated the above species into two genera. 



Jaw of Z. Binneyanus. [Morse.] 



