64 CETACEA. 



on the posterior half of the tympanic aspect is still 

 attached, apparently presents no characters by which it 

 can be distinguished from the periotic of H. rostratus in 

 the Museum of the Royal College of Surgeons (No. 2899), 

 and indicates the occurrence either of that or of a closely 

 allied species in the Pliocene. 



Made in the Museum, 1886. 



Genus CHONEZIPHIUS, Duveruoyi. 



Including Ziphirostrum, Du Bus ^. 

 Aporotus, Du Bus ^. 

 ZipMopsis, Du Bus *. 



This genus agrees with Mesoplodon in having the premaxillsB in 

 contact with the intervening bones throughout the length of their 

 inner surfaces, and in only showing a very small portion of the vomer 

 on the inferior aspect of the rostrum ; but differs in the non-ossification 

 of the mesethmoid cartilage in the rostrum, whereby there exists a 

 fistular excavation throughout the latter. The soldering of the inner 

 surfaces of the premaxillse is incomplete in some forms. The inter- 

 orbital space is flat ; and there are a pair of fossettes, of which the 

 right is the larger, in the narial region. The rostrum is compara- 

 tively short and thick. The posterior portion of the periotic is 

 rather longer than in Hyperoodon, the median ridge on the tym- 

 panic aspect of the same rather less strong, but the accessory ossicle 

 of nearly equal relative size. The genus occurs in the Tertiaries of 

 both Europe and North America, and may be regarded as con- 

 necting Hyperoodon with Mesoplodon. 



Choneziphius planirostris (Cuvier '). 



Syn. Ziphiiis planirosh'i^, Cuvier *'. 



This is the type species, and is of considerably larger size than 

 the existing Mesoplodon australis. The type cranium is figured in 

 the accompanying woodcut (tig. 12), and it seems doubtful if the 

 second cranium described by Cuvier under the same name, but 



1 Ann. Sci. Nat., Zool. ser. 3, vol. xv. p. 61 (1851). 



2 Bull. Ac. E. Belg. ser. 2, vol. xxv. p. 022 (1867). 

 •' Ihid. p. 626. 



' Ihid. p. 628. 



' Ossemens Fossiles, 2nd ed. vol. v. pt. i. p. 356 (1823).— ZzpAms. 



^ Loc. eif. 



