2<So WHALES AND DOLPHINS 



Mesoplodon densirostris is another rare species, characterized 

 by the massive development of the lower jaw teeth. They are 

 so large that the lower jaw is greatly modified to accommodate 

 the sockets in which the teeth roots are inserted. Where the 

 teeth are situated, about halfway along the jaw from the tip, 

 the upper margin of the jaw is raised into a crest from which 

 the crown of the tooth protrudes. The point of each tooth is 

 directed vertically upwards, and in a typical male specimen 

 the dimensions were : Length 6 inches, width front to hinder 

 margin 3! inches, width cheek side to tongue side if inches. 

 The soft tissues of the lower jaw are modified to conform with 

 the bony structure, the upper edge passes obliquely upwards 

 from the tip to the region of the tubercle bearing the tooth, and 

 then dips down again into a shallow concavity before reaching 

 the angle of the gape. 



The maximum length attained by this species is about 

 15 feet. Seven specimens are known from widely separated 

 places, including the Seychelles, Lord Howe Island, South 

 Africa, Massachusetts and New Jersey in the United States of 

 America and Madeira. 



In the Strap-toothed or Layard's Whale, Mesoplodon layardi, 

 the tooth modification reaches its extreme limit. The single 

 pair of teeth situated near the hinder end of the mandibular 

 symphysis of the lower jaws has each a small pointed enamel- 

 covered crown on the outside, borne on a flattened root portion 

 which grows longer with age, so that the free tip curves at first 

 upwards and backwards, then over the forward extension of 

 the upper jaw and, with its fellow, finally forms an arch 

 which only permits the lower jaw to open to a very limited 

 extent. 



A female specimen 16 feet in length is described by W. R. B. 

 Oliver in the ' New Zealand Journal of Science and Technology ', 

 1924. Referring to the dentition he says : " Each tooth is 

 triangular with the denticle well developed and projecting 

 outwards at right angles to the basal portion, which is entirely 

 enclosed in the alveolus. Although in the adult the teeth are 

 convex on the outer surface, in very young specimens the 

 outward-projecting denticle gives the appearance of the teeth 

 having the concave surface outwards." 



The body colour is said to be black above and white beneath, 



