84 CRETACEOUS AND TERTIARY FISH. 



Sub-Order MASTICURA. 



Tail comparatively slender, dorsal fin single or wanting, and 

 tail above usually armed with one or more serrated spines. 



This group comprises four families, of which the Ptychodon- 

 tidce are entirely extinct. Of the latter Ptychodus mammillaris 

 Agassiz has been ascribed to the Cretaceous of Delaware, though 

 no representatives have been found in New Jersey. 



Family MYLJOBATID^. 

 THE EAGLE RAYS. 



Disk broad. Nasal valves forming rectangular flap with pos- 

 terior margin free and attached by frenum to upper jaw. Ovo- 

 viviparous. Skull less depressed than usual among rays, its sur- 

 face raised so that eyes and spiracles are lateral in position. Skin 

 smooth. Tail very long, slender, whip-like, with single dorsal 

 near its root, behind which is usually a strong retrorsely ser- 

 rated spine. Pectorals ceasing at sides of head and reappearing 

 in front of snout as one or two cephalic fins supported by fin rays. 

 No differentiated spines in pectorals in males, sexes similar. 

 Ventrals not emarginate. 



The existing forms large sting rays in warm seas, feeding 

 chiefly on mollusks, which they crush with their large grinding 

 teeth. All the known six genera are represented by extinct 

 species, though only three of the former have persisted till the 

 present time. 



Genus MYLIOBATIS G. St. Hilaire. 



Myliobatis G. St. Hilaire. Descr. Egypt, 1809, PI. 26, fig. 1. Type Mylio- 



batis bovina G. St. Hilaire, second species. 

 Myliobates, auct. 



Ictcetus Rafinesque, Analyse de la nature, 181 5, p. 93 (nom nud.). 

 Ptychopleurus Agassiz. Poiss. Foss., Ill, 1838, PI. 45, figs. 1-3. Type 



Ptychacanthus faujasii Agassiz, virtually monotypic. 

 Holorhinus Gill, Proc. Acad. Nat. Sci. Phila., 1862, p. 331. Type Rhinoptera 



vespertilio Girard, virtually monotype. 

 Bates Probst, Jahresh. Ver. Vaterl. Nuturk Wiirtt., XXXIII. 1877, p. 88. 



Type Bates spectabilis Probst, monotypic. 



