The Embryology of Heterodontus japonicus 



671 



(Text'figure 10) there are 33 rows of teeth. The anterior teeth (13 series or transverse 

 rows) are distinctly tuberculate, but, due to the overlapping of the teeth in each row, 

 their form is not completely shown except in the most anterior members of each series . 

 Each anterior tooth possesses one large central cusp, and there may occasionally be seen 

 in the drawing a rudimentary lateral cusp on one or both sides of the central cusp. The 

 posterior teeth (ten rows on each side) are 

 large, smoothly rounded, and in their natural 

 arrangement combine to form an exposed 

 surface resembling that of a stone'block pave' 

 ment. Thus the anterior teeth are adapted for 

 holding the prey, the posterior ones for crush' 

 ing and grinding it. 



Striiver (1864) made drawings of the teeth 

 of both upper and lower jaws of Heterodontus 

 phillipi. With respect to the dentition, upper 

 and lower jaws are much alike, save that the 

 lower is slightly shorter and more obtuse in 

 front, which makes some difference in the 

 arrangement of the teeth. In this respect the 

 lower jaw resembles the jaw figured by Phillip 

 (1789) ; but in Striiver's figures both jaws show 

 a more gradual transition between anterior 

 (cusped) teeth and posterior (grinding) teeth, 

 so that the line of demarcation between the 

 two kinds of teeth is not sharply defined. 

 However, one might assign 15 transverse rows 

 to the anterior region in the upper jaw, and 13 

 rows to this region in the lower jaw. The total 

 number of teeth in the upper jaw is 33, in the 

 lower jaw 31. In Striiver 's figures the anterior 

 teeth are pointed but without obvious second' 

 ary cusps; each posterior tooth has an indistinct 

 longitudinal ridge. 



Miklouho'Maclay (in Maclay and Macleay, 



1879) figured the teeth of upper and lower jaws 



in both adult and young specimens of H. 



phillipi. The dentition of an adult, as shown in 



his figures (my Text'figure 11) resembles that ^ r ,, 



J c, 1 N A Text-figure 11. 



represented m Struver s drawmgs (1864). As ^^^^^ „f ^^ ^d^lt Heterodontus pMUpi: 



in Striiver 's figure, the lower jaw is shorter A, upper jaw; B, lower jaw. 



than the upper, and is more obtuse in front. After Maclay and Macleay, 1879, Figs. 16 and 17, pi. 24. 



