34 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL.69' 



inward. The apex of the crown is most strongly incurved on teeth 

 at the proximal end of the series and less so distally. None of these 

 teeth exhibit any trace of accessory cusps or tubercles. The enamel 

 on the crown is perfectly smooth; the basal margin of the enamel 

 crown is irregularly curved, but no cingulum is developed and the 

 enamel passes into the cementum of the root very gradually, with- 

 out any perceptible increase or decrease in the diameter of the neck.. 

 The penultimate maxillary and mandibular teeth are present on: 

 both sides. With the possible exception of the very long teeth (pi 

 8, fig. 1), the extremities of the roots of all the teeth curve back- 

 ward. In some instances there is a slight side to side enlargement 

 of the root below the crown. On such teeth both the upper part 

 of the root and the base of the crown are flattened anteriorly and 

 posteriorly. The mandibular teeth are similar to the maxillary in 

 form and size. Unfortunately the anteriormost mandibular teeth 

 are missing from both jaws, but the presence of an additional de- 

 tached tooth (pi. 8, fig. 1) indicates that the terminal tooth in 

 each mandible was elongated like its mate in the corresponding 

 premaxilla. 



Measurements of the teeth {in millimeters) 



Only one of the hyoid bones (pi. 1, fig. 1) is preserved and, judg- 

 ing from its size and other peculiarities, it is the right thyrohyaL 

 This bone is embedded in the matrix behind the left exoccipital and 

 its base is in contact with the transverse process of the atlas. In 

 Delphinodon dividv/m.', the lateral winglike thyrohyals are free and 

 are not anl^losed at the base with the basihyal. This may or may 

 not be due to immaturity. 



This right thyrohyal is at least 49 mm. long, 8.5 mta. wide at 

 the constriction near the base, and 11.5 mm. wide at the most ex- 

 panded portion. The extremity is buried in the matrix and the 

 proximal end or base is rugose for cartilaginous attachment to the 

 basihyal. This bone is thickest at the base and tapers to the distal 

 end; the posterior margin is nearly straight, but the anterior is 

 slightly convex. It differs from the thyrohyal of Delphinodon divi- 



