ELASMOBRANCHII. 77 



from the middle marl at Riddleton (Hackett's pits) and 1 with- 

 out data. 



Family SPHYRNID^. 

 THE HAMMER-HEAD SHARKS. 



Mouth crescent-shaped, under "hammer." Teeth in jaws 

 similar, oblique, each with notch on outside near base. Nostrils 

 anterior and eyes on side of "hammer." Last gill-opening over 

 pectoral. No spiracles. First dorsal and pectorals larg*e, and 

 dorsals nearer pectorals than ventrals. Second dorsal and anal 

 small. Pit at caudal root, single notch towards fin tip. 



Large sharks, among living forms easily distinguished by the 

 peculiar form of the head, which is slightly different in each 

 species. Though a number of generic names have been proposed, 

 they are now generally referred to the single genus Sphyrna. 



Genus SPHYRNA Rafinesque. 



Sphyrna Rafinesque, Ind. It. Sicil., 1810, pp. 46, 60. Type Squalus zygcena 



Linnaeus, virtually first species, restricted by Jordan and Gilbert, Bull. 



U. S. Nat. Mus., 1882, p. 26. 

 Sphyra, auct. 

 Cestracion (Klein) Walbaum, Pet. Arted. Gen. Pise, III, 1792, p. 580. Type 



Squalus zygcena Linnaeus, virtually first species, restricted by Gill, Ann. 



Lye. N. Hist. N. Y., VIII, 1861, p. 37. 

 Sphyrnias Rafinesque, Analyse de la nature, 181 5, p. — ? Type Squalus 



zygcena Linnaeus, virtually, as this name is offered to replace Sphyrna 



considered too short. 

 Cestrorhinus Blainville, Bull. Soc. Philomath. Paris, 1816, p. 121. Type 



Squalus zygcena Linnaeus, first species. 

 Zygcena Cuvier, Regne Animal, II, 1867, p. 27. Type Squalus zygcena Lin- 

 naeus, first species, by tautonomy, but preoccupied in insects. 

 Zygana, auct. 

 Platysqualus Swainson, Lard. Cab. Cyclop. N. H., II, 1839, p. 318. Type 



Squalus tiburo Linnaeus, monotypic. 

 Eusphyra Gill, Ann. Lye. N. Hist. N. Y., VII, 1862, pp. 403, 412. Type 



Zygcena blochii Cuvier, designated, monotypic. 

 Reniceps Gill, 1. c. Type Squalus tiburo Linnaeus, designated, monotypic. 



Characters of the genus expressed in those of the family. 

 About six existing species have been described, grading almost 

 perfectly from the narrow hammer of Sphyrna blochii to that of 



