PHTSETEEID^. 63 



Subfamily ZIPHIIN^E. 



In existing genera all the mandibular teeth are rudimentary, 

 with the exception of one or occasionally two pairs. 



Genus HYPEROODON, Lacepede l . 



There are a pair of small conical teeth concealed during life by the 

 gum at the extremity of the mandible. The upper ends of the 

 premaxillae rise suddenly behind the nares to the vertex, expanding 

 laterally, their outer edges curving backwards, and their anterior 

 surfaces arching forwards over the nares. There are large longitu- 

 dinal crests on the maxillae at the base of the rostrum. The poste- 

 rior portion of the periotic is shortened, the median ridge on the 

 tympanic aspect of the same very strongly developed, the accessory 

 ossicle large and rounded, and the anterior tympanic facette slightly 

 concave. All the cervical vertebras are fused together. 



P?j>perootton troStratuS (Miiller a ). 

 Syn. Balcena rostrata, Miiller 3 . 

 Hob. North Atlantic. - 



38140. A considerable part of the left ramus of the mandible ; found 

 in digging the main sewer in East Ham Marshes, Essex. 

 Presented by the Commissioners of the Metropolitan 

 Board of Works, 1864. 



Hyperoodon, sp. 

 Hob. Europe (England and [?] Belgium 4 ). 



M. 3536. Cast of the right periotic. The original, which was obtained 

 from the Red Crag of Suffolk and is preserved in the 

 Museum at Ipswich, is described and figured by the present 

 writer in the ' Quart. Journ. Geol. Soc.' vol. xliii. p. 14, 

 pi. ii. fig. 6. This specimen, in which the accessory ossicle 



1 Hist. Nat. des Cetaces Table d. Ordres&c., p. xliv (1804). 

 1 Zool. Dan. Prod. p. 7 (1776). Balcena. 



3 Loc. cit. 



4 The cervical vertebras of a species of Hyperoodon from the Antwerp Crag 

 are noticed by Van Beneden in the Bull. Ac. E. Belg. ser. 2, vol. x. p. 407 

 (1860). 



