88 



Table-case, 

 No. 32. 



Asterospondyli. 



the Carboniferous Limestone of Armagh, Ireland. The well- 

 known teeth of Ptychodus from the Chalk are proved to belong 

 to a large ray probably of the Myliobatis type, by specimens 

 both in this Museum and in the Brighton Museum. The arrange- 

 ment of the teeth in the jaws is shown in Fig. 117. Typical 

 portions of the dentition of Myliobatis occur abundantly in the 

 English Eocenes ; and the largest known specimen (M. Pentoni) 

 is exhibited from the Lower Tertiary of the Mokattam Hills, 

 Cairo, Egypt. Aetobatis and Rhinoptera are also Eocene. 



FIG. 117. Diagram of arrangement of teeth of Ptychodus decurrens, Ag.; English Chalk. 

 A, upper jaw ; B, lower jaw. 



SUB-ORDER II. Asterospondyli. 



Of the Asterospondyli or Sharks, the Notidanidae are 

 perhaps the most primitive surviving family. They are repre- 

 sented only by five or six species at the present day, and are 



MeZ 



FIG. 118. Skull of Notidanus, side view (after Wiedershehn). 



pq, pterygo-quadrate cartilage (upper jaw); md, mandibular cartilage; nk, nasal 

 capsule ; orb, orbit ; r, rostrum : ws, vertebral column ; >J< postorbital articula- 

 tion of the upper jaw with the cranium. 



noteworthy both on account of the primitive character of their 

 skull and backbone (Fig. 118), and for the possession of six or 

 seven gill-clefts instead of the usual five. Whole skeletons of 



