PLECTOGKATIIl. 



269 



which may be approximated to the Chondropterygii, with 

 which it is allied by the imperfection of the jaws, and the 

 tardy induration of the skeleton ; this skeleton, however, is 

 fibrous, and its whole structure is that of ordinary fishes. The 

 most distinguishing character of the order consists in the max- 

 illary bone being soldered to the side of the intermaxillary, 

 which alone constitutes the jaw, and in the mode in which the 

 palatine arch is connected with the cranium, which, being by 

 a suture, consequently renders it immovable. Besides this, the 

 opercula and rays are concealed under a thick skin, through 

 which only a small branchial fissure is visible.(l) Of ribs, 

 nothing is to be found but very small vestiges. There are no 

 true ventrals. The intestinal canal is ample, but without 

 C8eca,(2) and in almost every instance there is a large natatory 

 bladder. 



This order comprises two very natural families, character- 

 ized by their mode of dentition. 



FAMILY I. 

 GYMNODONTES. 



The Gymnodontes have jaws, which, instead of teeth, are 

 furnished with an ivory substance, internally divided into lami- 

 nae, whose ensemble resembles the beak of a Parrot, and which 

 in fact consists of true teeth united, that succeed each other 

 as fast as they are destroyed by trituration. (3) The opercula 

 are small, and there are five rays on each side, all of which 

 are but imperfectly seen. They live on Crustacea and fucus, 

 their flesh is mucous, and that of several species is considered 

 poisonous, at least in certain seasons. 



(1) This peculiai- arrangement, indications of which are visible in the Chiro- 

 nectes, has led several naturalists to believe that both opercula and rays are want- 

 ing in the Plectognathi; it is a mistake, however, for they are provided with them 

 like other fishes. 



(2) Bloch eiToneously atti-ibutes caeca to genus Dodon. 



(3) See my Legons d'Anat. Comp. vol. Ill, p. 125. 



