HOLOCEPHALI. 123 



cavity of largest dental area. Between anterior and lateral 

 dental areas on oral surface a concave depression extending- back 

 to largest dental area. Posteriorly on oral surface externally 

 edge arises in an elevated ridge, apex forming about opposite 

 concavity in largest dental area, surface inside evenly concave. 

 Inner surface of upper maxillary entirely flat. 



As Leidy pointed out, the dental areas appear as white chalky 

 friable spaces, which have more or less decomposed, leaving the 

 little more durable tubules of the vaso-dentine projecting from 

 their surfaces. He supposes originally tubecular structures were 

 found over the dental areas covering the dental columns, but 

 have now disappeared, leaving only their depressed and crum- 

 bling surfaces as now seen. These dental columns, corresponding 

 with the dental areas, may all be located at the posterior ends of 

 all the maxillaries. Length of longest lower maxillary 14 cm. 



I have described several of Leidy's types above, now in the 

 Academy, and note that the others agree in most respects, as he 

 has already remarked. At present they are a pair of maxil- 

 laries and two pairs of mandibulars. Another small example, a 

 right mandibular, agrees. It is from the New Jersey greensand, 

 and shows a few transverse crescentic stride on its damaged in- 

 ferior surface. 



Formation and locality. Known from the Cretaceous green- 

 sand at Barnsboro and Hornerstown [the Hornerstown marl 

 probably, K.]. According to Hussakof Ischyodus gaskillii Cope 

 and /. monolophits Cope, the types of which he has examined, and 

 which are now in the American Museum at New York, are a 

 small left mandibular, apparently of a young individual, and two 

 mandibular teeth, respectively, of the present species. 



I have also seen several examples in the collection of the 

 Geological Survey. They are a right and left mandibular from 

 the Cretaceous of "New Jersey," and one right and two left 

 mandibulars without data. 



Edaphodon miersii (Marsh). 



Dipristis miersii Marsh, Proc. Amer. Assoc. Adv. Sci., 1869, p. 230. Horners- 

 town, N. J. Upper Cretaceous Marl. 



Ischyodus miersii Cope, Rep. U. S. Geol. Surv. Terr., II, 1875, pp. 285, 292. 

 ("Hornerstown, Monmouth Co., N. J.) 



