4-10 Dr. R. Harlan on a new Fossil Genus, 



are hills of considerable size, composed almost entirely of fossil 

 marine shells and other organic reliquiae in a fossil state. 



My attention was first directed to this specimen by Mr. 

 T. Say, who with his accustomed liberality offered every as- 

 sistance in deciphering the same. At first view I recognised 

 it as a portion of the dental bone of an animal allied to the 

 Saurian reptiles: a closer inspection proved its approxima- 

 tion to the new fossil genus Ichthyosaurus ; an animal, as the 

 name imports, uniting in its structure both the fish and the 

 lizard; having the head of a lacertian animal joined to the 

 vertebras of a fish, and extremities entirely sui generis. For 

 a full description of this highly interesting animal, together 

 with another new fossil genus, the Plesiosaurus, naturalists are 

 particularly indebted to an able and elaborate essay, by the 

 Rev. W. D. Conybeare and Mr. De la Beche (in the Trans, 

 of the Geolog. Soc. 2d series, vol. i. part 1 ; and in vol. v.) in 

 which they have described four distinct species of the Ich- 

 thyosaurus. 



By the most critical examination of the present specimen, it 

 is found to possess characters which incontestably render it at 

 least specifically, if not generically, different from either. 



Our specimen, Plate III. is rendered doubly interesting by 

 its locality, being the first of the genus ever discovered on this 

 continent. While we have to lament that so small a remnant 

 of this animal has been snatched from oblivion, it still serves 

 to display the utility as well as beauty of the doctrine of the 

 laws of co-existence in the parts of animals, when employed 

 with that caution which renders it a legitimate instrument of 

 induction. A perfect knowledge of these laws enabled 

 Cuvier to establish important species, on data far less certain 

 than that now under consideration : not to mention many 

 others, the Anoplotherium medium was originally founded on 

 n portion of the lower jaw. 



From the data afforded by the account of the Ichthyosaurus 

 above mentioned, the following would appear to be its generic 

 characters: — Teeth fixed in an open sulcus, instead of separate 

 alveoli ; consisting of two series only, one growing within the 

 other ; anterior nares opening near the root of the snout, im- 

 mediately before the lachrymal bones. Bones of the head and 

 face, in number and structure, nearly resembling the Croco- 

 dile ; bodies of the vertebras concave both at their occipital 

 and caudal surfaces ; legs four in number, terminating in a 

 paddle, composed of a numerous series of polygonal bones, 

 and attached immediately to the distal extremities of the hu- 

 merus and femur ; anterior extremities much larger than the 

 posterior. Amphibious ? Oviparous. 



In 



