216 



it is developed outside of the pulp-cavity and fang of the old tooth, and takes its 

 place, as in many Lacertilia and in the Pytlionomorpha, by exciting the absorp- 

 tion of the latter. The conic form of these fangs in Saurocephalus is appro- 

 priate to such a succession, and their great length seems to preclude the 

 nutrition of the young tooth from their bases. The use of the foramina on 

 the inner face of the jaw is thus made apparent, viz, the nutrition of the 

 successional teeth from without. I cannot trace the canal below the crown 

 of the young tooth to the base of the pulp-cavity of the old tooth; and there 

 are canals in the jaw below the latter, one of which probably carried the 

 dental artery. 



Species of this genus are less abundant in the part of Kansas examined 

 by me than those of the preceding genera. Two only have been observed up 

 to the present time, as follows : 



Saurocephalus lancjformis, Harlan, I. c. 



Medical and Physical Researches, 3G2 ; Leidy, Transactions of the American Philosophical Society, 

 185G, plate. — Saurodon landformis, Hays, Transactions of the American Philosophical Society, 

 1830, 47C. 



Established on a right superior maxillary bone, from a locality near the 

 Missouri River. It differs from that of the other species in having a very 

 elongate superior suture with the premaxillary bone, and in the very short 

 dental crowns, which arc as wide as deep. The largest species ; known from 

 the jaw only. 



Saurocephalus arapaiiovius, Cope. 



Established on a portion of a maxillary bone with a pari of a suture, per- 

 haps for attachment to a supernumerary maxillary. The size of the species 

 is nearly that of 5. landformis, and the crowns of the teeth are rather short, 

 as in that species, and less elongate than in I), pltkbotomus. The teeth are 

 very closely set, and the fangs are separated by very narrow septa. The 

 crowns are expanded so that the edges overlap in some cases. The form of 

 these is much compressed: width about equal to height; the edges convex 

 and acute. The enamel is smooth and without facets. The roots are without, 

 the facets shown by Leidy to exist in S. landformis, and appear to be longer 

 than in that species, exceeding the length of the crown nearly four times. 

 None are, however, perfectly enough exposed for complete measurement. As 

 usual, there is a large foramen opposite each fang, below the inner alveolar 



