78 CETACEA. 



35592. An anterior left lower true molar, probably belonging to 

 this species ; from the Miocene (?) of North America. 

 The specimen shows minute denticulations on the anterior 

 border, and has very rugose enamel ; it agrees in size 

 with the teeth figured by Leidy in the ' Journ. Ac. Nat. 

 Sci. Philad.' ser. 2, vol. vii. pi. xxviii. 



Presented by Prof. J. W. Mallet, 1859. 



Family DELPHINID^E. 



The teeth are simple, and usually numerous in both jaws ; the 

 length of the mandibular symphysis may be very small, and never 

 exceeds one third of that of the ramus. The anterior facette on the 

 periotic (fig. 17) for articulation with the tympanic is deeply grooved, 

 and the posterior tympanic surface of the former is comparatively 

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

 tympanic ill-defined and situated close to one edge. 



Genus MONODON, Linn. 1 



The dentition is practically restricted to a single pair of maxillary 

 teeth, of which the left one in the male is usually developed into an 

 immense cylindrical tusk without enamel. The cervical vertebrae 

 are usually separate. 



monorrro*, Linn. 2 



This species is recorded by Owen 3 from the later deposits of the 

 Eastern coast, and has also been obtained from the Norfolk Forest-* 

 bed 4 . 



Hob. Arctic Seas. 



24576. Two lumbar and one caudal vertebrae ; from the Pleistocene 

 of Kotzebue Sound, Eschscholtz Bay, Alaska. 



Presented by Capt. Kdht and Lieut. Wood, R.N., 1850. 



Genus DELPHINAPTERUS, LacepMe 5 . 

 Syn. Bduga, Gray e . 



This genus is mainly distingished from Monodon by its dentition. 

 The teeth, which vary from | to ^, and occupy the anterior three 



1 Syst. Nat. ed. 12, vol. i. p. 105 (1766). 2 Loc. cit. 



3 British Fossil Mammals and Birds, p. 521. 



4 See Newton, Geol. Mag. dec. ii. vol. viii. p. 316 (1881). 

 8 Hist. Nat. d. Cetaces, p. ill (1804). 



6 Spicilegia Zoologica, vol. i. p. 2 (1828). 



