OF NEW SOUTH WALES. 323 



the lower ; in both jaws it was the fifth row (reckoning from be- 

 hind forwards) that proved to be the row of the largest teeth*. 

 In another case there were 33 rows in the upper jaw, and 32 in 

 the lower ; the row containing the largest teeth was the fourth in 

 the upper jaw, and the sixth in the lower. 



In an upper jaw of a H. Fliillipi much younger (smaller) 

 than the two just mentioned, I count 36 rows, the fifth being the 

 row containing the largest teeth. The number of the teeth in 

 the vertical rows are subject to variation ; the middle row** 

 of the upper and lower jaws has, in this case, 12 teeth, while the 

 row of the largest teeth contains 5 in the upper jaw, and 6 in 

 the lower. In the upper jaw of the young H. PhilUpi already 

 mentioned, the middle row numbers 14 ; the row of the largest 

 teeth consists of 7. The size of the teeth in proportion to one 

 another seems also to be by no means constant, while in some 

 specimens the length of the largest teeth exceeds that of the 

 teeth next in size by almost one- third ; the largest teeth of 

 another individual scarcely differed perceptibly in size from the 

 others. 



I could not ascertain whether all these variations in the num- 

 ber and size of the teeth are dependent on sex and age. The 

 material employed for the above descriptive remarks on the 

 dentition of the adult H, Phillipi consisted of dried jaws, to 

 which no note of the size and age of the animal had been ap- 

 pended. I have been unable to find time to fill up this hiatus 

 in the subject. 



3. — Dentition op Heteeodontds galeatus. Giinth. 

 If we compare the teeth, in a longitudinal row, in the adult 

 H. Phillipi from the anterior to the posterior members of the 

 series, we find that the cusps in the lateral teeth (in the anterior 

 third of the jaw) become blunter and blunter the larger the 

 teeth become, so that it takes the form of an elongated tubercle, 



* Dumeril says that it is tlie foicrth. (Hist. Nat. des Poissons. Tom. I., p. 137.) 

 This point may vary with the age or with the sex of the specimen. 



** Since, as is well known, the teeth of the Selachians are independent of the endo- 

 skeleton. (Vide Gegenbaur Grundzlige der Vergleichenden Anatomie, 2 Aufl. Leipzig., 

 1870, p. 783), a mesial row of teeth corresponding to the middle line of the body, though 

 occasionally present, is not always to be found. Dumeril made the same observation. 

 (1. c. p. 133.) 



