A FOSSIL TOOTHED CETACEAN FROM CALIFORNIA, 

 REPRESENTING A NEW GENUS AND SPECIES. 



(With Two Plates) 

 By FREDERICK W. TRUE 



A portion of the mandible of a fossil cetacean belonging to the 

 museum of the University of California, has recently been sent me 

 by Prof. J. C. Merriam and proves on examination to represent 

 an undescribed form. With the jaw are four detached teeth. This 

 material, which is recorded as No. 1352 Mus. Univ. Cal., was 

 obtained from Upper San Pablo, near Rodeo, California. Rodeo 

 is a town about 16 miles northeast of San Francisco on San Pablo 

 Bay. Although so small a part of the skeleton is available for study, 

 yet as it represents a quite distinct form, it seems to require a name. 

 It is, therefore, described below under the designation of Hespero- 

 cetas califormcus. 



The portion of the symphyseal region of the mandible preserved 

 consists of three fragments which, when placed in line, measure 

 196 mm. It is probable, however, that the anterior and middle 

 portions should be separated by an interval of about 30 mm. The 

 posterior portion is probably from near the posterior end of the 

 symphysis. The greatest breadth posteriorly is 41 mm. and the 

 greatest depth, 29 mm. In section, the mandible is triangular or 

 cordate, the sides being convex and the upper surface nearly flat. 

 When viewed from above, the jaw appears at first to present a 

 series of ten or eleven pairs of alveoli closely approximated, but 

 upon careful examination it is seen that every second pair in reality 

 consists of two shallow depressions in the surface of the jaw, while 

 the alveoli themselves are widely separated. There are, in fact, only 

 six pairs of alveoli represented in the fragment preserved, unless 

 the anterior pair is to be regarded as consisting of two or three pairs 

 of small alveoli closely approximated. Further reference will be 

 made to this question below. Aside from this anterior pair, the 

 alveoli are large and elliptical, the largest posterior one having a 

 longitudinal diameter of 20 mm. and a transverse diameter of 9.5 

 mm. They decrease in size anteriorly, the pair immediately follow- 

 ing the anterior ones having a length of 12.5 mm. The two alveoli 



Smithsonian Miscellaneous Collections, Vol. 60, No. 11 



