AND AVES OF NORTH AMERICA. 



63 



Tins genus presents the same peculiarity of dentition as the Plerodon Meyer (Diploey- 

 nodus Pomel) of the European Miocenes. The P. plenidens, and P. ratolii are both of 

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

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

 muzzle. 1 have seen but one cervical vertebra from American tertiarios, and that is of the 

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



Three species appear to exist in our Miocene beds. The 'I', sicaria indicates in its 

 lender 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 J have but one tooth of T. sicaria, three of T. antiqua and six of 

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

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

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

 antiquus they exist only towards the tip on the inner or concave lace 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. Boi., Phila., 1809, 8. 



This specie 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 then, from near (be 

 mouth of the Patuxont River, along with the remains of Eschrichtius, Physeter, and other Oetacea. 



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



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



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



istal extremity of the splenial bone. The slight degree of this obliquity indioates an extensive contact of these 



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



•io curvature appears at the anterior extremity of the fragment, and the alveolae are similar to those succeeding, it 



as 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 "I''"' 1 face " r Ul< ' radius is convex, most so anteriorly. Its lateral and inferior face is more convex than in 

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

 '"•'"una. 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 

 eeth 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 sm;,ll size which these 

 Parasites had attained ; and (bat it was buried in Miocene deposits and not worn by a more modern sea, is testified 

 o 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 

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



