Pisces — Plagiostomi and Ghimceroidei. 73 
Lias of Lyme Regis. On the adjoining pillar a large example of 
an extinct ray, I Ihinobatus bugesiacus, from the Lithographic stone 
of Bavaria, is exhibited ; and there are other smaller specimens, 
from a corresponding formation near Lyons, in the case. 
The first nine Table-cases on the West side of Gallery A. 
are also devoted to the Plagiostomi , and Ghimceroidei , com- 
prising the Carchariidce, Lamnidce , Notidanidce , Hybodontidce, 
Gestraciontidce , Myliobatidce , Paiidce , Torpedinidce , Squatinidce , 
Pleuracanthidce , and the Edaphodontidce, whose modern repre- 
sentatives, the sharks, rays, and chimseras, are most widely 
distributed in the seas of to-day. 
There is great difficulty in obtaining satisfactory evidence 
for the correct determination of these cartilaginous fishes in a 
fossil state. Thus in the sharks we have only the spines, teeth, 
and shagreen left : all else has disappeared, save some few of 
the vertebras in the Chalk and London Clay; the backbone of the 
earlier sharks appears to have been quite “ notochordal.” Even 
the spines and teeth are not always found in association in the 
same deposit, so that one cannot with certainty affirm that they 
belonged to the same fish. In many instances teeth and spines, 
originally placed in separate genera, have now been determined 
by correlation to belong to the same fish. Thus for example: — 
The spines named Pleur acanthus, from the Coal Measures, belong 
to the teeth called Diplodus, from the same beds. Asteracanthus 
spines found with Strophodus teeth are evidently parts of the 
same fish ; while Leptacanthus spines, found in the same matrix 
with Chimasroid jaws, in the Chalk, the Stonesfield Slate, and 
in the Solenhofen stone, furnish conclusive evidence of their 
union in the same fish. There can be no doubt that Myria- 
canthus spines in like manner belonged to extinct genera of 
chimeras. The teeth and spines of both Acrodus and Hybodus 
have now each been found in their true association, so that we 
know certainly the forms belonging to each genus. Again, 
many forms of crushing teeth which had been made into distinct 
species, are now known to occur in the jaws of the same fish. 
Th us the teeth named Strophodus magnus , and others named 
favosus , may be seen in the mandible of the same individual. 
The wide distribution, both geographically and geologically, 
of the sharks is very remarkable. Teeth of the genus Gar. 
charodon have been met with in Tertiary deposits in ISTew 
Zealand, Jamaica, Carolina, Malta, Egypt, in the Antwerp and 
Suffolk Crags, and elsewhere : and several species of other 
srenera are found common to the lower Tertiaries both of 
p 
Europe, America, and Australia. Sharks’ teeth, were also 
dredged up, in numerous localities, from the bed of the ocean 
during the voyage of H.M.S. Challenger, so that teeth of shai'ks 
will form a marked feature in the deposits now in process of 
formation in the depths of the sea. 
Gallery, 
No. 6. 
Fossil 
Fishes. 
Wall-case, 
No. 3. 
Sharks, 
Rays, and 
Chimseras. 
Table-cases, 
Nos. 25 to 
34. 
Teeth and 
Spines of 
Sharks. 
Acrodus 
and 
Hybodus. 
Carcharo 
don. 
Fossil 
Fishes. 
