MIOCENE PORPOISES — KELLOGG 115 



that of Inia. The dorsal border of the coronoid process is thickened 

 as in Inia. The distance from the apex of the coronoid process to 

 the hindmost alveola on the left ramus, however, amounts to about 

 30.5 percent of the total length, while in Inia it is equivalent to about 

 23.5 percent of the total length. The external face of the posterior 

 end of the left mandible is convex except for the shallow concavity 

 below the apex of the coronoid process. The dorsoventral axis of the 

 condyle is oblique, and its external border is projected beyond the 

 level of the outer face of the ramus. 



About 35 mm. behind the hindmost alveola and on the internal 

 surface of the ramus is the usual orifice for the large dental canal. 

 Posterior to this orifice the proximal end of the ramus consists mainly 

 of a thin outer shell, with the addition of thin internal shelving 

 strips that merge posteriorly with the upper and lower borders. 



Measurements of mandibles, USNM 15985 (in millimeters) 



Right Left 



Length of mandible, condyle to anterior end 540. 



Length of mandible as preserved, anterior end to 

 broken hinder end 520. 



Greatest length of ankylosed symphyseal portion 

 of rami 179. 179. 



Transverse diameter of ankylosed mandibular 



symphysis at level of hinder end 55. 



Vertical diameter of ankylosed mandibular sym- 

 physis at level of hinder end 32. 2 



Transverse diameter of ankylosed mandibular 



symphysis at anterior end 33. 8 



Vertical diameter of ankylosed mandibular sym- 

 physis at anterior end 



Height of mandible through coronoid process 



Height of condyle 



Breadth of condyle 



26 alveolae in an interval of 



14 hinder alveolae (1st to 14th) in an interval of 



12 anterior alveolae (15th to 26th) in an interval 

 of 170. 180. 



PERIOTIC 



The left periotic (pi. 5, figs. 1, 4) differs from that of Lophocetus 

 calvertensis (pi. 5, figs. 3, 6; USNM 16314) in that there is no osseous 

 projection below the cerebral orifice of the aquaeductus vestibuli, 

 the dorsoventral diameter of the extremity of the anterior jDrocess is 

 considerably less, the fossa for the head of the malleus is less vertical 

 in position, the anteroposterior diameter of the less noticeably in- 

 flated pars cochlearis is considerably less, and the depression on the 



