256 



CETACEA 



each side of the middle part of the upper jaw, but embedded by 

 their roots only in the gum, and not in bony alveoli. This fact, 

 Avith the frequent presence of rudimentary teeth in other species 

 of this and the last genus in both upper and lower jaws, 

 suggests the idea that the Ziphioids are derived from ancestral forms 

 which had teeth of normal character in both jaws ; the dentition 

 of the living forms having become greatly specialised. The existing 

 species of this genus are widely distributed in both northern and 

 southern hemispheres, but most frequent in the latter. The best 

 established are M. Helens, M. europceus, M. densirostris, M. layardi, 

 M. grayi, and M. hectori ; but there is still much to be learned with 

 regard to their distinctive characters and geographical distribution. 

 They were abundant in the Pliocene age, as attested by the fre- 

 quency with which the most im- 

 perishable and easily recognised 

 portion of their structure, the 

 long, cylindrical rostrum of the 

 skull, of more than ivory dense- 

 ness, is found among the rolled 



Fig. S7.— The left periotic bone of Meso- 

 plodon; from the Red Crag of Suffolk. The 

 smooth concave surface in the right upper 

 corner of the figure forms the anterior ar- 

 ticulation with the tympanic. (From the 

 Cat. Foss. Mamm. Brit. Mus. pt. v. p. 70.) 



and water -worn fragments of 

 animal remains which compose 

 the well-known "bone-bed" at 

 the base of the Red Crag of Suf- 

 folk. Several species have been 

 founded upon the evidence of 

 these rostra. Periotic bones of 

 this genus (Fig. 87) are of less common occurrence in the Crag ; 

 the figure is given to illustrate the characteristic features of this 

 bone in the present family. 



Berardius. 1 — Two moderate-sized, compressed, pointed teeth on 

 each side of the symphysis of the mandible, with their apices directed 

 forwards, the anterior being the larger of the two and close to the 

 apex. Upper ends of the premaxillse nearly symmetrical, moder- 

 ately elevated, very slightly expanded, and not curved forward over 

 the nares. Nasals broad, massive, and rounded, of nearly equal 

 size, forming the vertex of the skull, flattened in front, most 

 prominent in the middle line. Anteorbital notch distinct. Rostrum 

 long and narrow. Mesethmoid only partially ossified. Small 

 rugous eminences on the outer edge of the upper surface of the 

 maxillae at base of rostrum. Vertebrate : C 7, D 10, L 12, C 19 ; 

 total 48. The three anterior cervicals ankylosed, the rest free and 

 well developed. 



The only known species, B. arnuxi, attains the length of 30 

 feet, and has hitherto only been met with in the seas around New 

 Zealand. 



1 Duvernoy, Ann. Sci. Nat.-Zoologie, ser. 3, vol. xv. p. 41 (1851). 



