AND AVES OF NORTH AMERICA. 63 



This genus presents the same peculiarity of dentition as the Plerodon Meyei {Dvplocy- 

 nodus Pomel) of the European Miocenes. The P. plenidcns, and P. ratelii are Loth of 

 the Crocodilian type of cranium, the rami of the mandible with curved extremity and 

 short symphysis, while Thecachampsa is a gavial, Avith very long symphysis and slender 

 muzzle. I have seen but one cervical vertebra from American tertiaries, and that is of the 

 type of Thoracosaurus ; hence this character cannot be certainly ascribed to Thecachampsa. 



Three species appear to exist in our Miocene beds. The T. sicaria indicates in its 

 slender mandible one character of the genus ; it shows the surface to have been ridged 

 and pitted as in other Crocodilia. The T. antiqua Leidy indicates in its dorsal vertebra, 

 a smaller hypapophysis than in the known species of Crocodilus. T. sericodon Cope is 

 only known from its teeth. The teeth of the three species may be thus distinguished. It 

 must be mentioned that I have but one tooth of T. sicaria, three of T. antiqua and six of 

 T. sericodon. In the first the tooth has a lenticular section a short distance below the tip, 

 owing to the great development of the lateral cutting ridges, and the compression of the 

 crown at their bases. In the other two, these ridges are much less developed; in T. 

 antiquus they exist only towards the tip on the inner or concave face of the tooth, while 

 in T. sericodon they extend more than half the length of the crown towards the base, on 

 the inner side. 



THECACHAMPSA SICARIA, Cope. 



Proceed. Ac. Nat. Sei., Phila., 1869, 8. 



This species is represented by a lumbar vertebra, an imperfect crown of a tooth, and a portion of the under jaw. 

 They were submitted to me by Philip T. Tyson, State Geologist of Maryland, who procured them from near the 

 mouth of the Patuxent River, along with the remains of Eschrichtius, Physeter, and other Cetacea. 



The portion of mandible indicates an animal of a size considerably exceeding both the Gavial of India and the 

 Thoracasaurus of the Cretaceous of this country. It contains all or parts of alveolae of six teeth. Opposite the 

 fourth alveolus from the front, the margin diverges slightly from the median line, indicating the position of the 

 distal extremity of the splenial bone. The slight degree of this obliquity indicates an extensive contact of these 

 elements, and not a symphysis formed merely by union of the dentary elements as in Mecistops and Crocodilus. As 

 no curvature appears at the anterior extremity of the fragment, and the alveolae are similar to those succeeding, it 

 has evidently not been broken from the anterior portion of the symphysis. The nutritious canal of the ramus is thus 

 nowhere exposed, but is enclosed in the long symphysis. 



The upper face of the ramus is convex, most so anteriorly. Its lateral and inferior face is more convex than in 

 other Gavials which I have noticed, especially posteriorly. Its surface is coarsely sulcate, and with numerous small 

 foramina. A larger space than elsewhere is seen between the two median alveola?, which is occupied by a deep con- 

 cavity for the reception of a large tooth of the maxillary series. This indicates an irregularity in the size of the 

 teeth of that series, as in the Crocodiles, and not an equality as in other Gavials. On placing the fragment in position 

 the teeth are seen to have diverged at an angle of 45°. 



The specimen had laid sufficiently long in the Miocene ocean bottom to have been fixed upon by barnacles and 

 oysters, as a place of abode. That it had not remained unburied very long is evident from the small size which these 

 parasites had attained ; and that it was buried in Miocene deposits and not worn by a more modern sea. is testified 

 to by the Miocene shells (Turritella, etc.), whose fragments were removed from its cavities with the sandy clay of its 

 place of burial. The teeth have been broken off in this rough contact with the elements, but I procured a large and 

 characteristic portion of the crown of a successional tooth whose apex had attained to the level of the edge of the 



