ELASMOBRANCHII. 85 



Disk broad, pectoral fins not continued to snout end, ending on 

 head sides, and reappearing on snout front as one or two cephalic 

 fins supported by fin-rays. Tail very long, slender, whip-like, with 

 single dorsal fin near root, behind latter usually strong retrorsely 

 serrated spine. Nasal valves form rectangular flap, hind edge 

 free, attached by frenum to upper jaw. Teeth hexangular, large, 

 flat, tessellated, median usually broader than others. Skull less 

 depressed than usual among rays, surface raised so eyes and 

 spiracles are lateral in position. Ovoviviparous. Skin smooth, 

 without pectoral spines, and sexes alike. Ventrals not emar- 

 ginate. 



The existing species, about 15, are large sting-rays feeding 

 largely on mollusks Avhich they crush with their large grinding 

 teeth. They are found in most all warm; seas. About 80 extinct 

 species have been described. 



Myliobatis bisulcus (Marsh). 



Myliobates bisulcus Marsh, Proc. Amer. Assoc. Adv. Sci., 1869, p. 229. 

 Eocene greensand of Monmouth Co., N. J. 

 Leidy, Journ. Acad. Nat. Sci. Phila., (2) VIII, 1877, p. 239 (remarks). 



Dental plate with central row of teeth marked along median 

 line by a deep groove, otherwise remarkably smooth and flat. 

 (Marsh.) 



The account by Marsh is insufficient, and the species, may be 

 considered purely nominal until further elucidated. Leidy thinks 

 M. fastigiatusf may be the lower dental plate, in which case 

 Marsh's name would have priority. 



Formation and locality. The type was originally in the Mu- 

 seum of Yale College, and was from the Eocene [Shark River 

 K.] greensand of Monmouth County. 



Myliobatis fastigiatus (Leidy). 



Myliobates fastigiatus Leidy, Proc. Acad. Nat. Sci. Phila., 1876, p. 86. Mon- 

 mouth Co., N. J. Eocene. (No description). 

 Leidy, Journ. Acad. Nat. Sci. Phila., (2) VIII, 1877, p. 238, PL 31, fig. 

 n, PI. 33, fig. 6 (types). 

 Myliobatis fastigiatus Hussakof, Bull. Amer. Mus. N. H., XXV, 1908, p. 32 

 (type). 



