CESTRACION. 155 



Cestraciontidae. 



The single genus in this family differs from Carcharinus in the peculiar lateral 

 expansions of the skull across the frontal region, by which the eyes are carried 

 much farther outward. As in that genus there are no spiracles, the nostrils are 

 distinct from one another and from the mouth, the eyes have a well-developed 

 nictitating membrane, the teeth are compressed and blade-like, the labial folds 

 are rudimentary, and the first dorsal is in advance of the ventrals. The charac- 

 ters of the family are those of the genus Cestracion. Occurs in earl}^ Tertiary 

 formations. 



Cestracion. 



Cestracion Klein, 1742, Hist, pise, miss. 3, p. 12; 1776, Neuer schaupl., 3, p. 523; Walbaum, 1792, 



Artedi, p. 580. 

 Sphyrna Rafinesque, 1810, Indice, p. 60. 

 Cestrorhinus Blainv., 1816, Bull. Soc. philom., p. 121. 

 Zygaena Cuv., 1817, Reg. anim., 2, p. 127. 

 Sphyrichthys Thienemann, 1828, Lehrb., 3, p. 408. 

 Platysqualus Swains., 1839, Class., 2, p. 318. 

 Sphyra Hoeven, 1858, Handb., 2, p. 68. 

 Reniceps Gill, 1861, Ann. N. Y. lyc, 7, p. 403. 

 Eusphyra Gill, 1861, ibid. 

 Cestracion Gill, 1861, ibid. 



Body, behind the head, similar to that of Scoliodon and its closer allies. 

 Head much depressed, with a broad oculonarial expansion at each side. JMouth 

 inferior, greatly arched forward. Teeth compressed, triangular, broad based, 

 with cusps more or less obliquely directed toward the angles of the mouth and 

 notched on the outer edges. Labial folds rudimentary. Eyes distant from the 

 middle of the head; a nictitating membrane. No spiracles. First dorsal above 

 the space between the pectorals and the ventrals. Second dorsal above the 

 anal. Caudal with pits at its origin, and with a produced subcaudal lobe. 



Head hammer-shaped, very wide 



eyes and nostrils widely separated 



oculonarial expansion wide, slender . . hlochii (page 156) 



eyes and nostrils close together 



oculonarial expansion medium, oblique 

 concavity above the nostril deep 



cusps of teeth prominent . . . zygaena (page 157) 

 concavity above the nostril moderate 



cusps of teeth low, very oblique . . oceanica (page 158) 



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