ON CTENODUS. 417 



arched, the lower margin being regularly convex ; the symphy- 

 sial surface is not distinguishable, and was probably formed 

 chiefly by the cartilage that undoubtedly occupied the groove 

 or channel of the inner surface. 



The teeth (d) are placed on the upper border of the expanded 

 portion, and extend in a close series of from six to eight from 

 the posterior extremity almost to the junction of the border with 

 the anterior semicylindrical portion of the bone : the dentary 

 area is thus very limited. The teeth are small, short, stout, co- 

 nical, and obtusely pointed, and seem to be firmly anchylosed to 

 the bone. 



The dentary bone has apparently been united to the articular 

 piece by a squamose suture ; but however this may have been, 

 it is evident that the attachment was only slight, as the two 

 bones are frequently found detached. 



The maxillary teeth are well developed ; they are larger than 

 those of the mandible, are stoutish at the base, decidedly re- 

 curved and sharply pointed ; but we are unable to determine 

 their number and arrangement, on account of the disturbed con- 

 dition of our specimens. There are teeth on both the maxillae 

 and premaxillse. In addition to these dental organs, the vomer 

 is armed with close-set, minute, rounded tubercles or teeth. 

 This is undoubtedly the same spatulate dentigerous bone figured 

 and described in the 12th Decade of the Geological Survey by 

 Professor Huxley as the parasphenoid or vomer in Macropoma : 

 in form and position it is very similar. 



Ctenodus, Agassiz. 



The body-scales of Ctenodus are entirely unknown, with the 

 exception of those of C. elegans and C. obliquus, which we de- 

 scribed some time ago* — the former in a good state of preserva- 

 tion, the latter in a less perfect condition. We have, however, 

 obtained from time to time numerous fragments of large scales, 

 so frequently associated with the remains of the larger Ctenodi, 



* Ann. Nat. Hist. Ser. 4, Vol. I., p. 77. 



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