The Embryology of Heterodontus japonicus 



673 



the anterior teeth (my Text'figure 12) of a not fully developed Heterodontus phillipi 

 761 mm. (22.1 inches) long are distinctly tricuspidate, the central cusp predominating, 

 while those of the adult become almost pavement-like, with an inconspicuous cusp. He 

 further states that on the posterior teeth of a young specimen 418 mm. (16.4 inches) long, 

 a longitudinal ridge is much more pronounced than in older specimens. 



Maclay (Maclay and Macleay, 1879) portrayed also the dentition of both upper and 

 lower jaws in their very young specimen of Heterodontus phiUipi only 225 mm. (8.8 inches) 

 long. Comparatively few teeth are exposed (my Text-figure 13) and these are nearly all 

 cuspidate. About 40 teeth are visible on the upper jaw and about 32 on the lower jaw, 

 roughly arranged in transverse rows of two or three teeth each, giving about 17 rows on 

 the upper jaw and 13 on the lower jaw. Most of these teeth have three to five cusps, and 

 seldom a predominating central cusp. The cusps are best developed in the most anterior 

 teeth and are less conspicuous posteriorly. They are absent in one or two teeth of 

 the last row on each side. Maclay states that some other teeth came into view after the 

 mucous membrane had been dissected off. He calls attention to "the very great similarity" 

 between the dental armature of the young Heterodontus and that of (adult?) Notidanids. 







'ky 



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Text-figure 14. 

 Head and teeth of the Port Jackson Shark, Heterodontus phillipi, in three aspects: A, 

 anterior view of the head, mouth closed, showing exposure of teeth above and below. 

 B, teeth of lower jaw in natural si2;e. C, mouth widely opened, to show the similarity 



of dentition above and below. 

 After McCoy, 1890, pi. 113. 



