PISCES. 
75 
case 8 , are unusually good specimens. The well-known Wall-ease 
teeth of Ptychodus (Fig. 74), from the Chalk, seem to Tabl g‘ cases 
belong to a skate intermediate between these families and 7^3 
the Myliobatidse or “devil fishes.” An extensive collec¬ 
tion is exhibited in Table-case 8 . Typical portions of the 
dentition of Myliobatis itself occur abundantly in the English 
Eocenes, but the largest known specimen (M. pentoni) is 
from the Eocene of the Mokattam Hills near Cairo, Egypt 
(Table-case 8 ); Aetobatis and Rhinoptera are also Eocene. 
Skin-tubercles of the existing Raja occur in the Pliocene 
Crag (Fig. 75). 
Sub-class II.— Holocephali. 
The Chimseroids do not differ much from the Elasmo- Wall-case 
branchs, except in the fusion of the upper jaw-cartilage 3 - 
with the skull; but fossils have not hitherto revealed any a |" case 
fishes definitely intermediate between these two Sub-classes. 
Fig. 76.—Left mandibular tooth of Edaphodon leptogiiathus, inner view, 
from the Middle Eocene of Bracklesham Bay, Sussex; about two-thirds 
nat. size. (Table-case 9.) 
The teeth are large and reduced to not more than two pairs 
in the upper jaw and one pair in the lower jaw, while the 
whole dentition is shaped much like a beak. 
Typical Chimseroid teeth, Rhynchodus and Ptydodus , are 
found in the Devonian of North America and Europe; but 
some isolated teeth of this age are so peculiar that the}^ may 
be either Chimseroid, Sirenoid (p. 76) or Arthrodiran (p. 79). 
The first satisfactory skeletons are those of the Jurassic 
period, and some are exhibited in Wall-case 3 . The skeletous 
of Squcdoraja, from the Lower Lias of Lyme Regis, are 
especially well preserved, and prove this fish to have been 
shaped like a narrow skate, with a long snout and a long 
tapering frontal spine in the male, but no dorsal fin-spine. 
Myriacctnthus, from the same formation and locality, resembles 
