78 CLASS XIV. 



Family X. Gymnodontes Cuv. Jaws at the anterior part 

 exsert from the mouth, covered with an ivory substance made up of 

 very small concrete teeth. 



In these fishes the three anterior branchial arches alone carry 

 gills, the fourth does not. 



The structure of the teeth has been described by Cuvier (Zej?. 

 cVAnat. comp. iii. pp. 126, 127, PI. 32, fig. 8), and afterwards with 

 greater detail and exactness by Owen {Odontography, pp. 77 — 82, 

 PI. 38, 39). Besides the dental envelope in front of the jaws, there 

 is seen in Diodon in the upper and lower jaw, behind the margin, a 

 flat tubercle divided in the middle, with transverse striae on the 

 surface, formed by the projecting edges of transverse laminae of teeth 

 placed one behind the other. In some species of Tetrodon a similar 

 tubercle with enamelled teeth, but miich smaller, is found in the 

 upper jaw; in others it is wanting both in the upper and under 

 jaws. 



Orthragoriscus ScHN. Body compressed, not aculeate, trun- 

 cated. Maxillas undivided in the middle. Dorsal and anal fins 

 remote, high, united with the caudal at the posterior truncated part 

 of the body. 



Sun-fish. The fishes of this genus have no swimming-bladder ; their 

 branchial membrane has six rays. Behind the smooth margin of the jaws, 

 which is invested with dental substance, are some small conical teeth arranged 

 irregularly. Since the jaws are undivided in the middle, these species ought 

 in the arrangement of LlNN^us to be referred to the genus Diodon, although 

 he placed the species known to him under Tetrodon. 

 Sp. Orthragoriscus mola ScHK., Tetrodon mola L., Willughb. Tab. i. 26, 

 Bloch Icth. Tab. 128, Sun-fish, Domsma, Verhandel. van de Haarl. Maatsch. 

 XII. 1770, bl. 413 — 422, with a figure. The skeleton, heart, and intestinal 

 canal are described and very beautifully figured in P. H. J. Wellenbergh 

 Diss, inauff., Observ. anat. de Orthragorisco viola, L. B. 1840, 4to. (From 

 the bony pieces at the margin of the caudal fin in the specimen described by 

 W., it has been imagined that it belongs to the genus Ozodura Ranzani ; 

 but at all events it is a different species from that described by E., as is 

 proved not only by the different number of the fin-rays, but also by the form 

 of the body, which in Ozodura Orsini is elongate.) 



The genera Ozodura, Trematojisis and Diplanchias of Eanzini, as also 

 the genera of the same vsTiter founded upon the division of the under-jaw, 

 or of both jaws, Tympanium and Cephalus, are unknown to me, but seem 

 not to be sufficiently established, and, partly at least, to rest upon insecure 

 or incorrect detenninations. See Ranzani's memoir in Nov. comment. Acad. 

 Scimtiarum Bononiensis 1839, of which Troschel has given an epitome in 

 Erichson's Archiv f. Naturgesrh. 1841, 11. s. 140, 141. 



