278 NORTHERN ZOOLOGY. 



CHONDROPTERYGII ELEUTHEROPOMI. 



STURIONIDE^E. 



The Cartilaginous fishes (those whose skeleton contains no bony fibres, but 

 only small calcareous grains) are considered by Cuvier as forming a series parallel 

 to the osseous fishes, in the same way that the marsupial animals represent the 

 unguiculated mammalia. They are not, in his opinion, either inferior or superior 

 in their organization to the osseous fishes, for many of the genera approach the 

 reptiles in the structure of the ear and genital organs, while others show so much 

 simplicity of form, and such imperfect vestiges of a skeleton, that one might even 

 hesitate in ranking them among the vertebrated animals. The two orders into 

 which the series is divided are characterised by the condition of the gills. The 

 eleutheropomi * resemble ordinary fishes in their gill-openings, which are furnished 

 with a cover edged by a greatly-restricted membrane destitute of rays. This order 

 comprehends only two genera or families, one of which, acipenser of Linnaeus, or 

 the Sturionidece, is included by M. Agassiz along with the plectognathi, syn~ 

 gnathi, and fifty extinct genera in his order of Ganoidians; his Placoidians em- 

 bracing the rest of the cartilaginous fishes. The following Sturionidece have been 

 mentioned by authors as existing in the waters of the United States. Acipenser 

 brevirostris, Le Sueur ; A. rubicundus, Id. ; A. oxyrhynchus, Id. ; A. macu- 

 losus, Id. ; Plalirostra edentula, Id. ; Polyodon spatula, Regne Animal. 



[117.] 1. Acipenser transmontanus. (Richardson.) Columbia River 



Sturgeon. 



Family, Sturionideae. Genus, Acipenser. Aucr. Sub-genus, Sterleta. Brandt. 



The sturgeons resemble the sharks in general form, but their bodies are de- 

 fended by bony shields disposed in five, or in a few instances in three, longitudinal 

 rows ; their head is also well cuirassed externally ; their toothless mouth, situated 



* Donati opercuiis branchialibus hberis, Lovetsky. Eleutheropomes. Dumeril. 



