238 ZOOLOGY. 



are furnished with card teeth. The American species are : Amhlypterus 

 nemopterus and A, punctatus, from New Haven. 



We now proceed to take up tiie consideration of the cartilaginous 

 Ganoids, or the Chondrostei, which are represented in the hving fauna by 

 the SturionidcB, and are characterized by the cartilaginous vertebral column, 

 and by other features, which will appear in the description of the families. 

 The genera of the Sturionid^ are all found in America, two of them being 

 peculiar to it. 



In Polyodon the snout is enormously prolonged, and much dilated, and, 

 together with the head, is nearly as long as the body. The gape of the 

 mouth is very wide, and the operculum is prolonged behind into a 

 membranous flap, this reaching beyond the middle of the fish. The tail, 

 as ir all Chnndrostei, is highly heterocercal, and the skin entii'ely naked. 

 The single species Polyodon folium, is an inhabitant of the waters of the 

 Mississippi, where it attains to a size of five feet, although usually not more 

 than one or two. It bears the various names of spoonbill, spade-, paddle-, or 

 shovel-fish, and is by some considered a great delicacy for the table. The 

 teeth are very distinct when young ; but when old, the species become 

 edentulous, in which state it has been mistaken for a different form. 



In Acipenser the fusiform body is prolonged into an acute Snout, 

 projecting beyond the transverse protractile mouth, and with several 

 depending cirri. The skin is furnished with several rows of large plates, 

 more or less developed, with ganoid granules, or smaller plates, interspersed. 

 O'i the larger plates there is one row on the back, one on each side, and 

 two or more on the belly. The preoperculum is absent, and the caudal 

 termination of the vertebral column is provided with a fin above. The 

 sculpture on the head, and the arrangement and character of the plates, 

 furnish good specific characters. The American species of this mostly 

 fluviatile species have not yet been distinctly defined ; the number, 

 however, is quite considerable. They bear the generic name of sturgeons, 

 and attain to a great size. The oil is sometimes collected for economical 

 purposes, and the flesh by some is highly esteemed. On the Hudson river 

 it is called " Albany beef," from its frequent exposure in the markets of 

 that city. The European Acipenser ruthenus, and A. slurio, are repre- 

 sented in pi. 81, figs. 24 and 25. It may perhaps be worthy of mention, 

 that most of the isinglass of commerce is furnished by the air-bladders of 

 sturgeons. In the genus Scaphirhynchus, found associated with Polyodon, 

 we have a much greater development of the dermal plates than in 

 Acipenser. The posterior half of the body is entirely embraced by these 

 sharply angular plates, and is of a remarkably depressed, though highly 

 attenuated form. The upper edge of the caudal extremity of the body is 

 bordered by imbricated scales, instead of regular fin-rays. The snout, 

 also, is broader, and moi^e shovel-shaped than in Acipenser, and the whole 

 fish more slender. But one species, the Scaphirhynchus platirhynchus, or 

 shovel-fish of the Mississippi waters, is known. 



The remaining families of the Chondrostei are composed of entirely 

 extinct species, and among them we find the oldest forms known to the 

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