NORTH-CAROLINA GEOIX5GICAL SURVEY. 



221 



face of the young tooth (Fig. 39) is very rough, and the edges 

 of the rugosities are realy, irregularly serrate, and run into 

 each other. The section is round at all places, from the base 

 to the apex. Its crown is hollow, and its pulp cavity presents 

 a conical hollow which extends about one-third of the length 

 of the crown. On exposure to the weather, the crown ex 

 foliates in conical layers. Below the crown, that part known 

 as the root is hollow, but has a thick strong shell, which on 

 the concave side has three wide shallow furrows ; the middle 

 one is exactly in the concavity ; they occupy about one-third 

 of the cylinder; the remainder is perfectly circular. 



Prof. Owen s description of the polyptychodon* is as fol 

 lows : &quot; Teeth thick and conical ; transverse section of the 

 crown circular, without larger or trenchant ridges ; enamel 

 ridged longitudinally, but only a few reaching the apex. 

 The crowns, when weathered, exfoliate in a conical manner 

 by detached layers, like a cone in cone; base having a con 

 ical pulp cavity which opens into the crown in distinct 

 sockets.&quot; 



The foregoing description of Prof. Owen, of the genus Po- 

 lyptychodon, applies so well to our teeth, that there can re 

 main scarcely a d oubt as to their generic identity. It is, 

 however, only a generic similarity ; the species appears to be 

 quite different from both of the species described by Prof. 

 Owen, and from its remarkable rugose enamel, I propose as 

 its specific name, rugosus. 



It differs from the Alligator in the absence of a deep con 

 striction at the base of the crown, from the Pliogonodon of 

 Leidy, by its robustness and rugosities, and from the Ellipton- 

 odon, by its circular section, this having a circular section only 

 at the base of the crown, while in the former the crown haa 

 a circular section from base to apex. 



Sculptured Cranial Plate, (Fig. 40.) These plates are sep 

 arated from each in the line of suture, and are generally bro 

 ken. They are thick and strong, and were no doubt sufficiently 



* Palaeontographical Society s transrction, p. 46, rol. for 1851. (Description of th* 

 P. interuptus and continuus.) 



