6 PROCEEDINGS OF THE NATIONAL MUSEUM vol.66 



The crown of the third mandibular tooth is broken off obliquely 

 in an interno-external direction. The enamel forms a band en- 

 circling the crown of the tooth, about 1 mm. in thickness and ap- 

 proximately 35 mm. in depth when complete. The crown and upper 

 part of a tooth which broke away from the end of the root in the 

 mandible at the time the specimen was removed from the sea cliff 

 measures 153 mm. in length. The greatest transverse diameter of 

 the base of this apical section of the tooth equals 68 mm. and the 

 maximum thickness of the cement is 9.5 mm. At the level of the 

 superior face of the mandible, the outer coat of cement varies from 

 10 to 19 mm. in thickness. From these measurements it is evident 

 that a short section of the root which intervenes between this apical 

 portion and the distal extremity is missing. A large mandibular 

 tooth will measure at least 300 mm. in length. The roots of these 

 teeth are fusiform, remarkably robust, and very large in proportion 

 to the crown. They are almost straight at the basal two-thirds, but 

 curved toward the crown so that the latter appears to be obliquely 

 placed upon it. 



Tlie enamel on the crown does not form an enlargement at the base 

 and passes into the cement on the root without any perceptible in- 

 crease or decrease in the diameter of the neck. Hence there is no 

 distinct neck and no constriction at this point can be observed on any 

 of the teeth which are sufficiently preserved to offer any data. The 

 distal extremities of all the teeth are present in the left mandible. 

 At their upper ends, a small pulp cavity is exposed in the second and 

 ninth teeth, measuring 3.5 and 7.5 mm. respectively in diameter. This 

 indicates that the lower portions of the roots were pervaded by a 

 slender pulp cavity, irregular in diameter because of the presence of 

 nodosities on the sides. 



As seen in cross section, the teeth consist of an internal cone of 

 ossified pulp and dentine which is covered externally by a thick layer 

 of cement. This outer coat of cement is usually brownish in con- 

 trast to the light cream-colored dentine, and on the eighth tooth of 

 the right mandible is equal to about one- fourth of the transverse di- 

 ameter of the root. The dentinal axis is formed in concentric layers 

 while the cement on the other hand appears to be composed of thin 

 and narrow longitudinal strips or laminae. In cross section, the ends 

 of these laminae are so arranged that their axes correspond to lines 

 radiating from the center of the pulp cavity. 



The most obvious distinction between these teeth and that of 

 Ontocetus emmonsi is the relative thickness of the outer layer of 

 cement. In cross section the central axis of dentine appears to be 

 more or less ovoidal in the anterior mandibular teeth in contrast to 

 the circular outlines of the posterior ones, but this may be due in 



