256 
THE GEOLOGIST. 
Stonesfield, tlic more pcvfect specimens in some instances retaining 
tlie serrated sockets by which they were inserted in the jaw. Fine 
specimens of the defensive fin- spines (lehthyodorulites) of these 
Hybodi are sometimes found. These singular fossils were at one 
time regarded by naturalists as the jaws of fishes ; they are now, 
however, ascertained to be the defensive weapons of sharks, the sup- 
posed teeth that in some species arm their concave sides, being the 
hooks or prickles to which the membrane of the fins was attached. 
Several living species of the great family of sharks have smooth 
horny spines connected with the dorsal fin, and similar small tooth- 
less spines occur in a fossil state in the chalk formation. Ten species 
of the genus Ganodus represent the Edaphodontidse. The Ganoid 
fishes of Stonesfield belong to the four famihes Pycnodontidae, Lepi- 
doidei, Sauroidei, and Caslacanthi. The Pycnodontidte are repre- 
sented by the genera Pycnoclus, Gijrodm, Gijwnrhus, and Scaplwdus. 
The remains of this family most frequently found are the small round 
palatal teeth of Pycnochis trigonus, generally occurring in an insulated 
condition, but sometimes met with in small groups retaining the 
position they once occupied in the jaw. The family Lepidoidei has 
only two genera as its representatives in the formation under review, 
namely Lejndotus and PJiolidnphorus. These are distinguished by 
their enamelled scales, rhomboidal in form, and in some species 
smooth and glistening, but in others cuiiously plicated or folded. 
Small jaws are also sometimes obtained belonging to Lepidotus tuher- 
culatus (?) ; these retain the teetli in a considerable degree of perfec- 
tion. The Sauroidei are represented by the genera Saurojms, 
Caturus, Macrosemius, and Belonostomus. The fishes of this vora- 
cious family combine both in the structure of their bones and some of 
their soft j^arts characters belonging to the class of reptiles. The 
Sauroid fishes are distinguished by their beautifully striated teeth, 
nearly conical, with conical cavities like the teeth of Saurians. In 
some species the base of the tooth is fluted like that of the Ichthyo- 
saurus. The nearest analogues presented to these fishes in the 
existing creation are the Lepidosteus, or bony pike of North 
America, and the Polypterus of the South African coast. Of the 
Cffilancanthi only a single species, Ctenolepis clyclm, is known at 
Stonesfield. 
From the fishes of Stonesfield we ascend to its reptiles, the most 
famous of which is the Megalosaurus BucJclandii. The thigh-bones 
of this animal measui'ed three feet, and the leg-bones, which were 
hollow, the same length ; and the vertebrae were also of great size. 
Portions of its jaws, armed with long thin serrated teeth curved in 
the form of a pruning knife, are preserved in the Oxford Museum. 
From these remains, Dr. Buckland conjectured this enormous 
lizard to have been twice the length of a crocodile, or thirty or 
forty feet. 
Associated vntli the Megalosaurus are found the remains of another 
samian of considerably smaller dimensions (Teleosaurus Gadomensis), 
possessing affinities with the recent crocodiles. Those strange flying 
