Berry and Gregory — Prorosmarus alleni. 447 



The detailed description of the specimen is as follows : 



Prorosmarus alleni gen. et sp. nov. 



Mandibular ramus complete except posteriorly, the coronoid 

 process and the region of the mandibular angle being broken 

 off at a point which leaves the inferior dental canal (8 mm in 

 diameter) centrally located and on a horizontal line with the 

 alveolar border. The jaw is extremely massive throughout 

 and is vesicular anteriorly and along the alveolar region. The 

 canine alone is in place and from its worn appearance indicates 

 an old animal, as does also the character of the whole specimen. 



Dental formula. — The dental formula of the lower jaw is 



I— — — , C— , P , M-, but judging by analogy with the 



walrus one or more of the true molars may have been present 

 in the young jaw, and even as vestiges, without alveoli, in the 

 adult. It would be interesting to know whether the milk teeth 

 were better developed than in Odobcenus, as Flower believed 

 that in Odobcenus the vestigial milk teeth " never cut the gum, 

 but are absorbed rather than shed," this process commencing 

 before birth. In the upper jaw there must have been three 

 incisors (the existence of the outer pair being plainly indicated 

 by the worn antero-internal face of the lower canine), a canine 

 not nearly so much enlarged as in Odobcenus, four premolars 

 and possibly one or more much reduced molars. The outer 

 lateral incisor, like its opposing tooth the lower canine, had not 

 yet been taken over into the molariform series. Thus the com- 

 plete dental formula of the adult was probably If, Cf, Pf- My. 



The internal incisor (% of the typical Eutherian formula) 

 was evidently considerably reduced in size as compared with 

 the other teeth, but still functional, and was apparently retained 

 in the specimen until after the death of the animal. It is placed 

 almost behind the outer incisor, decumbent, directed forward 

 at an angle of about 45°. Alveolus round, 8 ram in diameter and 

 2 cm in depth. The outer incisor (i 3 ) is large, approximately 

 paralleling the canine in direction. Alveolus 13xl5 mm in 

 diameter, the longest diameter being transverse ; depth 5 cm . 



Canine — Bluntly conical, directed slightly forward and out- 

 ward and curving slightly backward, nearly circular at the base 

 in cross section but slightly flattened anteriorly. Much worn 

 on the antero internal quadrant, presumably by the attrition of 

 the upper outer incisor. Height 2*2 cm , diameter l-7 om , diastema 

 l*4 cm . The premolars were all rounded, simple and deep-set. 

 The first alveolus indicates a vertical, slightly forward direction 

 and is l-7 cm in diameter and 4'4 cm in depth. The second alveolus 

 indicates a slight outward and forward direction and is l - 8 cm in 

 diameter and 4 cm in depth. The third alveolus is very slightly 



