294 



A similar tooth, nearly the same size but slightly more sigmoid, is repre- 

 sented in Fig. 96, page 244, of Professor Emmons's Report of the North 

 Carolina Geological Survey, published in 1858. Tiie specimen is attributed 

 to the Miocene Tertiary, and is referred to a species with the name of 

 Pycnodus caroHnensis. 



HADRODUS. 

 Hadrodus priscus. 



The genus above named is obscure in its relations, and was originally 

 described in 1857, in the Proceedings of the Academy of Natural Sciences 

 of Philadelj)hia. It was founded on a specimen consisting of a bone with 

 two singular-looking teeth, discovered by Dr. William Spilhnan, in the Cre- 

 taceous formation in the vicinity of Columbus, Mississippi. 



The specimen represented in Figs. 17 to 20, Plate XIX, I have supposed 

 to be a jiremaxillary bone of an animal allied to the extinct genus Placodus, 

 ■formerly considered to be a pycnodont tish, but now determined to be a 

 sanropterygian reptile, 



The bone is nnsymmetrical, and sujiports two strongly co-ossified teeth. 

 Whether the specimen is complete in itself or whether it is part of a larger 

 bone, I have not been able to ascertain. 



The bone is quadrate in outline; thicker and longer on one side, and 

 oblique at the upper border. The anterior surface is convex and compara- 

 tively smooth. On each side and extending posteriorly, the bone is deeply 

 excavated into large reserve cavities for successional teeth. The back surface 

 between the cavities inclines from each side, forming a median angular groove 

 descending to the interval of the teeth. The bone is more porous and striated 

 posteriorly than anteriorly. 



The teeth remind one of the premolars of some pachyderm, rather thau 

 the teeth of a fish or reptile. They are not exactly alike, and are co-ossitied 

 with the bone by a firm osseous base or root, striated in front. They are 

 quadrate in outline, with the breadth and height nearly the same, and the 

 thickness about half. The crown is convex in front and at \he sides, and is 

 bilobed at the triturating border, which slopes off posteriorly. An acute 

 ridge and the conical blunted summits of the lobes define the outer from the 

 inner surface. Smooth enameloid substance invests the crown, extending" 

 twice the depth on the outer surface that it does on the inner suritice. In 

 transverse section the teeth are ovoid. 



