4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



ridge is bifurcated upward to a point about half way between the 

 base of the crown and the apex (when complete). 



The dimensions of the portion of the mandible which is pre- 

 served are as follows : 



mm. 



Length of the three parts when in line and touching 196 



Greatest breadth of median portion posteriorly 41 



Least breadth of anterior portion anteriorly 26 



Breadth at middle of median portion 34 



Length of posterior alveolus 20 



Breadth of the same 9-5 



Length of alveolus next to the anterior one 12.5 



Breadth of the same 9 



Length of anterior alveolus 22 . 5 



Breadth of anterior alveolus 12 



Length of the posterior depression 18 



Breadth of the same n -5 



Length of one of the middle depressions 16 



Breadth of the same 10 



Length of the depression next to the anterior alveolus 8 



Breadth of the same 10 



Least breadth of median ridge between alveoli posteriorly. ... 9 



Least breadth of median ridge between alveoli anteriorly. ... 4 



Depth of mandibular fragment posteriorly 29 



Least depth of mandibular fragment anteriorly 23 



From the foregoing description it will be gathered that Hespero- 

 cctus californicus is a toothed cetacean, or porpoise, of moderate 

 size, with a rather long beak and teeth in both jaws. The teeth 

 were separated by wide interspaces, those of the lower jaw fitting in 

 between those of the upper jaw and vice versa when the mouth was 

 closed, but probably the teeth of neither set touched those of the 

 other in front or behind, except in a few instances. The tips of the 

 upper teeth probably rested on the upper surface of the lower jaw in 

 the depressions which intervene between the alveoli, and, similarly, 

 the mandibular teeth probably rested against the roof of the mouth. 



What the affinities of the species are is difficult to determine. The 

 peculiar setting of the teeth just mentioned reminds one, to a certain 

 extent, of the South American genus Ischyrorhynchus Ameghino. 

 The original description of the type-mandible of Ischyrorhynchus 

 vanbenedeni is as follow^: 



" Mandibular rami anchylosed together throughout the length of 

 the tooth-row as in Saurocetes [=Pontoplanodes]. Mandible less 

 compressed, with a flat and rugose space between the two tooth-row 5, 

 one or two centimeters broad in its posterior part. Perpendicular 



