PLATE VIII. 



Enchochi!^ petrosus Cope. 



This specimen, No. 198 in the American Museum, has been figured in 

 part, and described as a new species (E. Sxvits) by Dr. O. P. Hay, but 

 since it displays several features heretofore not discussed, it was thought 

 best to refigure it. 



vt, a vertebra. The fragmentary hyomandibulars (hm) are placed with 

 their dorsal ends upward and their cephalic edges inward on the plate. The 

 larger bone between them represents the dorsal aspect of the caudal end 

 of the skull ; />, the left frontal. The sutures in the skull are too indistinct 

 to be traced. The broken lines represent approximately the outer margins 

 of the cephalic ends of the frontals. These bones should join firmly to 

 the ethmoid, eth (cf. pi. XI, fig. 1, and pi. VI, figs. 3 and 4). pal, palatine; 

 pni.r, the premaxillaries. The cephalic ends are placed downward on the 

 plate. In life the mesial edges probably approximated each other. Near 

 the mesial edges are two elongated foramina, the right one nearly one- 

 fourth longer than the left. On the eephalo-ventral edges are the bases 

 of a single row of teeth. 



The left palatine of this specimen furnishes a fine illustration of the 

 manner in which the new fang originates. The old fang has been broken 

 off, but a considerable portion of the new base remains. This is much 

 flattened on the cephalic side, obviously due to the absorption of the 

 osteodentine. Over this flattened surface there has been deposited a 

 porous layer of new bone tissue, which in time evidently would have 

 hardened and thickened sufficiently to form the base for a new fang. 

 This is the only specimen examined by the author, which shows this 

 particular state in the replacement of the palatine fang. It is doubtless 

 perfectly normal and furnishes a substintial cori-oboration of the theory 

 of the replacement of palatine fangs in Enchodus. 



