5*6 



GANOIDS. 



2760, and a second 3200 lbs. Migratory in its habits, this sturgeon crowds into 

 the Russian rivers as the ice is breaking up, when many individuals are more or 

 less severely injured by being jammed against the floes. It appears that only full- 

 grown fish ascend some rivers, as no small ones are found in the Danube ; but in 

 the Volga these sturgeon are stated to remain during the winter in a semi-torpid 

 condition. Although extremely powerful, the hausen is an inactive and timid fish, 

 fleeing even from the diminutive sterlet, and passing much of its time on the mud 

 at the river-bottom, but rising occasionally to swim near the surface. In diet it is 

 both carnivorous and herbivorous, feeding on vegetable substances, other fish, 

 especially various kind of carp, and even water-fowl. Its isinglass is inferior to 

 that of the common sturgeon. Rarely visiting the British coasts, where it is a 

 " royal " fish, the latter species has only from twenty -six to thirty-one lateral plates, 

 and from eleven to thirteen down the middle of the back ; the muzzle peing pointed, 

 and about equal to one-half the length of the head. It is a widely distributed 

 form, frequenting the coasts of both sides of the Atlantic, but absent from the 

 Caspian, although found in the Black Sea. In Italy it ascends the rivers from 

 March to May ; and while in that country it does not commonly exceed 5 or 6 feet 

 in length, specimens of upwards of 18 feet are on record. 

 Shovel-Beaked The four species of the genus Scaphirhynchus (which must not 



sturgeons. b e confused with the toothless sturgeons) differ from the preceding 

 genus by the production of the muzzle into a spatulate beak, by the narrow and 

 depressed hinder portion of the tail being completely covered by the bony plates, 

 as well as in the absence of spiracles, and by the fin-rays not surrounding the 

 extremity of the upper lobe of the tail, which terminates in a long filament. Of 

 the four species, one is restricted to the Mississippi river-system, while the others 

 inhabit the rivers of Central Asia ; all being exclusively fluviatile in their habits. 

 Allied Extinct The genera Chondrosteus and Belonorhynchus from the European 



Families. L{ as severally represent two families differing from all the modern 

 sturgeons in the absence of a median unpaired series of bones in the head-shield, 

 and also in the possession of branchiostegal rays. In the latter family the tail is 

 diphycercal, and there are longitudinal series of bony plates on the body ; whereas 



in the former the tail is heter- 

 ocercal, and the body is either 

 naked or with a small series of 

 scales on the upper lobe of the 

 tail ; both being furnished with 

 teeth. 



The scaled 

 types of this sub- 

 order are so utterly unlike the 

 sturgeons in external appear- 

 ance that it is only by a study 

 of their internal structure that 

 their true affinities have been 

 determined. They are all 

 extinct, and mainly character- 



Scaled Types. 



an extinct ACIPENSEEOID fish {Platysomus), from the 

 Magnesian Limestone. 



