SPERM WHALES AND BOTTLE-NOSED WHALES 277 



found in the lower jaws, and their position and form gives some 

 guide to the different species encountered, but as the teeth 

 are usually concealed beneath the gums in female animals 

 during life they are not very useful for distinguishing the 

 species when only a superficial examination can be made. 

 Within individual species the body colour itself is not constant, 

 and external markings are insufficiently conspicuous to help in 

 identification. 



The name Mesoplodon implies " armed with a tooth in the 

 middle of the jaw ". and refers to the position in the lower jaw 

 of the teeth in the first species to be described — Sowerby's 

 Whale (M. bidens). In this species the pair of teeth is situated 

 at some distance behind the tips of the lower jaws. It is useful 

 in the description of the species of Mesoplodon to have some 

 fixed point of reference for the position of the teeth in the jaw, 

 and for this purpose the hinder end of the junction (the mandi- 

 bular symphysis) of the two branches of the lower jaw is used. 

 It will be seen presently that not all the species of Mesoplodon 

 conform to the description implied in the generic name where 

 the position of the teeth is concerned, for in some the teeth 

 are situated as near to the apex of the lower jaw as it is 

 possible for them to be. 



In adult animals belonging to this genus the forward exten- 

 sion of the skull forming the rostrum or beak is a dense rod-like 

 mass of bone. It derives its solidity from the ossification of a 

 cartilaginous structure situated between the bones of the upper 

 jaw and its coalescence with them. 



The commonest species is Sowerby's Whale, a creature 

 which attains a length of some 16 feet. The head is more 

 slender and tapering and the forehead more receding than in 

 other Beaked Whales. The dorsal fin, flippers, flukes and 

 throat grooves show no marked variation from the typical 

 Ziphioid pattern. The body colour is black or bluish-black, 

 sometimes grey or white on the under surface. Harmer, 

 describing one specimen, says : " Certain parts were grey, 

 namely the anterior edges of the tail-flukes, part of the lower 

 jaw (which was partly white) and the upper jaw, which had 

 white edges." As in Cuvier's Whale, scratches and marks 

 on the skin are believed to be caused by the teeth of animals 

 belonging to the same species. 



