SüB-CLASS I 



SELACHII 



43 



I 



Family #12. Myliobatidae. Müller and Henle. Eagle-rays. 



Trunk much depressed, forming a broad disk with the very large ptdoxaLfins^ 

 which are interrupted at the sides of the head, hut reappear as one or a pair of small 

 cephalic fins at the extremity of the snout. Tail very slender, with one or several 

 flattened sphies hehind the single dorsal fin. Teeth rather large, forming a dose 

 pavement in both jaws. Skin naked. Cretaceous (?), Tertiary and Recent. 



Most of the survivirig genera of this family are represented iii the Tertiary 

 by isolated teeth and spines, or by the complete dentition. 



? Ftychodus, Ag. (Aulodus, Dixon), (Figs. 85, 86). Known only by the 

 dentition and vertebrae, and hence of uncertain systematic position. Teeth 

 quadrangular, with a raised crown, which is 

 transversely or radially ribbed, and sharply 

 separated by a constriction from the smaller, 



Fig. 85. 



Ftychodus polygyras, Ag. Tooth, ural and posterior view; 

 nat. sizf. Greensaiid ; Kegensbnrg. 



Fig. 86. 



Ftychodus decurrens, Ag. Uiagrain of 

 arrangeinent of teeth in npi)er(^), and 

 Iower (B) jaws, niuch reduced. Lower 

 Chalk ; England (after Smith Wood- 

 ward). 



smooth root. The teeth are solid, and the ganodentine investing the crown 



is thick. They are arranged in about thirteen antero-posterior series (Fig. 



86). In one jaw, presumably lower, the median series of teeth is the .largest, 



and the lateral rows are dis- 



posed symmetrically, diminish- 



ing in size outwards. In the 



opposing jaw the median series / /K ^ _ _— /y<^\ 



is very small, and the first / / fXl^^^y_ ir^ 



.T;nvs of Recent Myliobatis, lateral aspect. 



Jaws of MylinhoMs aquüa, Cuv. Anterior aspect. Recent : 

 Mediterranean (after Agassiz).. 



lateral row on each side large, with the outer lateral series diminishing. 

 Common in the Chalk of Europe and North America, rarer in the Greensand. 



