ICHTHYOSAURUS. 65 



Dr. Koenig first described this genus under the name of 

 Ichtkynsaurus, and Sir E. Home has called it Proteosaurus, 

 (see Phil. Trans. 1814.) 



The teeth are conical, longitudinally striated, the crown 

 enamelled, and internally hollow, sunk in a deep groove in 

 the jaw, with a pit at the bottom for each tooth ; they are 

 replace<l like those of the crocodiles. Palate toothless. 

 The muzzle is nearly entirely formed of the intermaxillaries ; 

 the maxillaries are placed on the sides at the base, and the 

 nasal at the upper part of the base. The nostrils are placed 

 between the nasal, the intermaxillaries, and the anterior 

 frontal. The frontal, parietal, occipital, petrous, sphenoid, 

 and pterygoid bones are very like those of the lizards, espe- 

 cially the Iguance. The orbits are surrounded by the front and 

 hinder frontal and the cheek bones ; the temporal holes by 

 the temporal and mastoid. The eyes are very large, and the 

 sclerotic coat is strengthened, as in birds, by a series of bony 

 plates. The lower jaw is united together for half its length. 

 The vertebrae are numerous, 48-49, all nearly similar, the 

 articulating surfaces concave, as in fish. The ribs appear to 

 be united like those of Chameleons cind Anoles ; the shoulder 

 bone and sternum resemble those of the lizards. 



The paddles are formed of five or six series of bones, simi- 

 lar to the phalanges of the Dolphins, but more numerous, 

 there being; often 20 — 25 in each series ; the series are of 

 nearly equal length, only tapering so as to bring the paddle 

 to a point. 



Nothing is yet known of its external coat. The ears are 

 probably wanting. 



Head about a quarter the length ; tail about a quarter 

 shorter than the body. Cuvier believes that they respire 

 free air by lungs, and are capable of seeing in the night. 



1. Ichthyosaurus communis, Cuv. Os. Fos. v. t. 29, f. 1, 

 9, t. 28, f. 9, 10, t. 29, f. 11, 12, 13. 



Teeth, crown conic moderately acute slightly arched and 

 deeply striated ; with two angular prominences at the root of 

 the nose between the orbits. 



2. Ichthyosaurus platyodon, Cuv. Os. Fos. v. t. 28, f. 4, 

 5, (dens.) 



Teeth, crown compressed, with a sharp ridge on each side. 

 Length 15 feet. 



K 



