96 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



panic) are round, relatively small, and distinct, characters which readily 

 distinguish this element from Delphinoid periotics. 



Delphinidae. 



The anterior facette of the periotic for articulation with the tympanic 

 is deeply grooved, the posterior tympanic surface of the former is com- 

 paratively narrow, and its ridge for articulation with the free border of 

 the tympanic is ill-defined and situated close to one edge. The attach- 

 ment of the two elements to the cranium is secured by ligaments only, 

 not by bony union. Porus acusticus relatively large and of oval outline. 



Delphinus. 



Although the ear-bones of the type species, D. delphis Linne present 

 easily recognized peculiarities, yet, owing to the restricted sense in which 

 the generic term is now employed, 1 it does not appear possible to formu- 

 late a diagnosis from such minor details which will enable us to distin- 

 guish this genus from all other Dolphins by means of ear-bones alone. 

 It is to be noted that some of the "Albatross" ear-bones agree very 

 closely with the existing D. delphis, the resemblance being closer than 

 with any known fossil species ; yet we cannot be sure of absolute specific 

 identity. 



Comparisons v:iih recent forms. — The remark just made with refer- 

 ence to Delphinus applies also to Kogia, a genus which has not been 

 recognized with certainty in the fossil state, and is represented by at 

 least three well-characterized living species. The few deep-sea ear-bones 

 which have been obtained do not differ in any material degree from 

 those of the supposed nearest ally of Physeter, Kogia breviceps. Three 

 examples are shown in Plate 3, Figs. 24-26, and one very perfect spec- 

 imen has been figured in an earlier Report. These may all be assumed 

 to belong either to the pygmy sperm whale or to a closely allied species. 



The case of Hyperoodon is somewhat different, inasmuch as the deep- 

 sea ear-bones referred to this genus cannot be identified either with the 

 existing H. rostratus or with any known fossil form. Although it is 

 clear that a distinct species is represented, no necessity appears for 

 designating it by a new name, for the simple reason that no satisfactory 

 diagnosis can be framed upon the evidence of ear-bones alone. The 

 principal differences to be noted between the "Albatross" material 



1 True, F. W., Review of the Family Delphinidae. Bull. 36, U. S. Nat Mus., 

 (1889), 191pp., pi. 46. — On Species of Soutli American Delphinidae described by 

 Dr. R. A Philippi in 1893 and 1896. Proc. Biol. Soc. Wash. (1903), 16, p. 133-114. 



