Recherches sur les Poissons Fossiles. 339 



2nd. Fam.— SAUROIDES, Agass. 

 Teeth conical, pointed, alternating with tufts of little teeth, 

 scales flat, rhomboidal, parallel to the body, which is all 

 covered. Skeleton bony. 



A. Body elongated, fusiform; superior lobe of the caudal 

 vertebras longer than the inferior ; Pygopterus. t. xii. f. 2. 

 Acrolepis. 



B. Body elongated, fusiform, caudal regular. Ptycholepis 

 Sauropsis, Pachycormus, Thrissops, Urceus, Leptolepis, 

 Megalurus, and Macropoma. 



C. Body very elongate, cylindrical; caudal regular; jaws 

 prolonged. Saurostomus and Aspidorhynchus. 



3rd. Fam.— PYCNODONTES, Agass. 

 Teeth a little flattened or round, in many ranges, scales 

 flat, rhomboidal, parallel to the body, which is all covered. 

 Skeleton bony, body flat, large. Placodus. Sphoerodus. 

 Pycnodus. t. xii. f. 3. Gyrodus and Microdon. 



4th. Fam. — SCLERODERMES, Cuv. 

 Palatine arch immovable ; muzzle prominent, armed 

 with some distinct teeth. Scales flat, and formed in large 

 rhomboidal or polygonal plates placed obliquely to the body, 

 which is all covered. Skeleton fibrous, but little ossified. 

 Ostracion. 



5th. Fam.— GYMNODONTES, Cuv. 

 Palatine arch immovable ; jaws covered with an ivory 

 sheath formed by the union of teeth. Scales raised to points 

 or hooks. Skeleton fibrous, ossification slight. Diodon. 



6th. Fam.— LOPHOBRANCHES, Cuv. 



Branchies united in little round tufts. Body elongate, 

 angular, covered with angular plates ; muzzle tubular, ter- 

 minating by little thin jaws. Skeleton osseous. 



These are the leading groups of one of the orders of 

 M. Agassiz, which is placed at the head of the class of 



