LAMPREYS AND FISHES OF INDIANA. 163 



of mud is taken in with the food. Sturgeons have been observed dig- 

 ging up the soft bottom with their snouts. 



Sub-class 2. HOLOSTEI. 



Primitive skeleton extensively ossified. Head fully protected by 

 membrane bones. Body clothed with enameled bony plates or with 

 cycloid scales. Opercular apparatus well developed. Branchiostegals 

 present. Tail heterocercal, but not so strongly so as in the Chondrostei. 



Two orders are recognized ; these include fishes which are the modern 

 representatives of forms that were abundant during former geological 

 periods. 



* Snout long ; dorsal fin short and far back, Ginglymodi, p. 163. 



** Snout short and blunt; dorsal very long. Halecomorphi, p. 167. 



Order 3. GINGLYMODI. 



This order is distinguished by many remarkable characters. The 

 bodies of the vertebras, instead of being concave at both ends, as in other 

 fishes, are strongly convex in front and concave behind. Each side of 

 the lower jaw is composed of five bones, as in many reptiles. The maxil- 

 lary bone is transversely divided into several pieces. 



The body is elongate. The short dorsal and anal fins are situated 

 close to the caudal. The head is produced into a long snout, and the jaws 

 are armed with teeth which contain a pulp cavity, and the walls of which 

 are fluted or folded. The order contains the family Lepisosteidtv. 



Family LEPISOSTEID^E. 

 THE GAR-FISHE8. 



^Form elongated and subcylindrical. Head long, terminating in a de- 

 pressed snout; covered with enameled bones. Mixillary, premaxillary, 

 and lower jaw furnished with sharp conical, fluted teeth. Dorsal and 

 anal fins small, set near the caudal. Body covered with hard, enameled, 

 "rhomboidal scales. 



A single genus, containing fishes which are of great interest to the 

 student of biology, but which are of no economic value. 



Genus LEPISOSTEUS Laeepede. 



Upper jaw longest. Both jaws with large teeth set among numerous 

 smaller ones, the larger teeth fitting into pits in the opposite jaw. Pala- 

 tines with small, sometimes also with large, teeth. No teeth on tongue. 

 Gill-rakers present, short. Gill-membranes broadly attached across the 

 isthmus and free from it. Lateral line present. Ventrals situated 

 about the middle of the body. Young with the tail ending in a filament. 



