256 



THE GEOLOGIST. 



Stonesfield, the more perfect specimens in some instances retaining 

 the serrated sockets by which they were inserted in the jaw. Fine 

 specimens of the defensive fin- spines (Ichthyodorulites) 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 sj)ecies 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 families Pycnodontidse, Lepi- 

 doidei, Sauroidei, and Cselacanthi, The Pycnodontidae are repre- 

 sented by the genera Pycnodus, Gyrodus, Gyronchus, and Scaphodus. 

 The remains of this family most frequently found are the small round 

 palatal teeth of Pycnodus 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 Lepidotus and Pliolidopliorus. These are distinguished by 

 their enamelled scales, rhomboidal in form, and in some species 

 smooth and glistening, but in others curiously plicated or folded. 

 Small jaws are also sometimes obtained belonging to Lejpidotus tuher- 

 culatus (?) ; these retain the teeth in a considerable degree of perfec- 

 tion. The Sauroidei are represented by the genera Sauropsis, 

 Cakirus, Macrosemius, and Belonostomus. The fishes of this vora- 

 cious family combine both in the structure of their bones and some of 

 their soft parts 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 I^'orth 

 America, and the Polyp terus of the South African coast. Of the 

 Ceelancanthi only a single species, Ctenolejjis clyclus, is known at 

 Stonesfield. 



From the fishes of Stonesfield we ascend to its reptiles, the most 

 famous of which is the Megalosaurus BucJdandii. The thigh-bones 

 of this animal measm*ed three feet, and the leg-bones, which were 

 hollow, the same leng-th ; and the vertebrae were also of great size. 

 Portions of its jaws, armed with long thin serrated teeth curved in 

 ihc 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 thnty or 

 forty feet. 



Associated with the ]\Iegalosaurus are found the remains of another 

 saurian of considerably smaller dimensions (Teleosaurm Cadomensis), 

 possessing aflfiiiities ^\dth the recent crocodiles. Those strange flying 



