cuvier's system. 77 



VI. Chondropterigious. Gills and bones cartilaginous. 



60. Acipenser. I 62. Squalus. I 64. Petromyzon. 



61. Chimffira. | 63. Raia. | 



The above arrangement is so far natural^ that it pre- 

 serves in a distinct group all the cheloniform fishes 

 (Plectognatlies , Cuv.) whose body is encased in a coat of 

 mail, or covered with hexagonal scales, and which more 

 especially differ from true fish in having the branchia 

 concealed and the operculum fixed. This, which we 

 have shown to form a primary group, is placed next to 

 the chondropterigious order, where the skeleton becomes 

 entirely cartilaginous. The apodal order, had it been 

 restricted to the eel-like fishes, would have corresponded 

 in its contents to ours ; but there seems no reason what- 

 ever for placing the sword-fish (^Xiphias) next to OpJiu 

 diiim, or Leptoceplialus next to Steryioptyx. The three 

 next orders, of Jugular, Thoracic, and Abdomiiial, 

 are excellent as artificial groups, enabling the student, 

 by attention to the single circumstance of the position 

 of the ventral fins, to ascertain the nomenclature of his 

 specimens. 



(75.) The system of Cuvier, and of his able coad- 

 jutor Valenciennes, will now be more particularly de- 

 tailed, as given in the last edition of the Regne Animal, 

 The primary divisions are two: — the first composed 

 of what are called true or osseous fishes, having the bones 

 solid ; the second are the Chondroptet^ygii, or cartila. 

 ginous fishes. In these latter the bones of the lower 

 jaw are supplied by those of the palate. 



(76.) Osseous, or true fishes, are divided by our 

 author, in the first instance, into two most unequal 

 assemblages : — 1. Those in which the gills, or branchia, 

 are pectinated ; and, 2. those in which they resemble 

 a series of small tufts. All true fishes come under the 

 first of these divisions, excepting the genera Syngnathus 

 and Pegasus of Linnaeus, which constitute M. Cuvier's 

 order Lophohranchii. The first division of osseous 

 fishes is again divided into two groups of equal dis- 



