INTRODUCTION. 5 



Centracion derives from Kivrpov and aKis, or possibly kioju, and is better 

 suited to the genus. An earlier name for the Port Jackson Sharks, Hetero- 

 dontus, had been bestowed by Blainville, 1816, in disregard of the fact that 

 Heterodon, identical in derivation, was applied by Latreille, 1802, to a 

 genus of snakes. Blainville is followed by some authors, but, as his name 

 is preoccupied in snakes, and as Cuvier's name, Cestracion, had been ap- 

 plied to a very different genus of sharks, Centracion becomes the earliest 

 substitute as a generic name for the Port Jackson Sharks. It is not found 

 that Gray made any explanations. He wrote Cestracion instead of Centra- 

 cion in his synonymy when, in 1851, he adopted the name Heterodontus 

 for the genus; having dropped the name Centracion explanations were 

 unnecessary. The apparent displacement in the earlier literature of recent 

 and fossil forms is not as great in the change to Centracion, as would appear 

 in the use of Heterodontus, Tropidodus, or Gyropleurodus of later dates. 



AcANTHiDiUM. — As published by Lowe, 1839, in Proc. Zool. soc. London, p. 92, 

 this genus contained two species, A. pusillum and A. calceus. The first 

 was a species of Etmopterus Raf., 1810; its removal from Acanthidiam 

 left A. calceus the type and only known species of the genus. 



Dalatias. — This is not recognized as a genus. Rafinesque, 1810, gave as a 

 principal character no spiracles. Under the name he placed two species; 

 one of which was possibly a species of Squalus, with spiracles and dorsal 

 spines; the other has not been identified from the description and the figure. 

 It has a large first dorsal near the pectorals, a small second dorsal distant 

 from the ventrals and is without spiracles. Bonaparte, 1846, suggested 

 that Dalatias might have been the genus named by himself Scymnorhinus, 

 and Gray, 1851, and others following him, adopted the suggestion; but 

 Scymnorhinus licha Bonn, and Bonap., the species under consideration, has 

 a small first dorsal behind the pectorals, a larger second dorsal, above the 

 ventrals, and has spiracles, sufficient reasons to discredit the identity. 



Rhina. — Klein's genus Rhina, 1742, Hist. pise, miss., 3, p. 13, and 1776, Schau- 

 platz, 2, p. 587, and of Walbaum, 1792, Art. Gen. Pise, p. 580, had for .'ts 

 type Squalus squatina Linn6, 1758. The name Squatina was used instead 

 of Rhina by Valmont, 1768, but without mention of a type. 



Rhinobatus. — Klein's Rhinobatus, 1742, Hist. pise, miss., 3, p. 32, and 1776, 

 of the Schauplatz, 2, p. 593, was drawn from Aristotle, Pliny and others 

 by way of Columna, 1744, Phytob., p. 101, pi. 27 ('Ptro/3aros sive Squati- 

 noraia, on the plate). The reference in the Schauplatz fixes the type as 



