GYMXODOXTES. 269 



Fam. 2. GYMNODONTES. 



G3'mnodontes, Cuv. Reyne Aiiiinal. 



Body more or less shortened. The bones of the 

 upper and lower jaw are confluent, forming a beak 

 with a trenchant edge, without teeth, with or without 

 median suture. A soft dorsal, caudal, and anal are 

 developed, approximate. No spinous dorsal. Pectoral 

 fins ; no ventrals. 



Mannc fishes of the temperate and tro])ical regions. Some species 

 confined to fresh water. 



Si/no^sis of the Groups and Genera. 

 First Groxip. Triodontina. 

 Tail rather long, with a separate caudal Jin ; abdomen dilatable into 

 a lanje conijrressed sac, supported Inj a long pelvic bone. Air- 

 liladdcr present. 

 The upper jaw divided by a median suture, the lower simple. 



1. Triodvn, p. 270. 



Second Group. Tetrodontina. 

 Tail and caudal Jin distinct. Part of the asophagus much exten- 

 sible, and capable of being Jilled ivith air. ]\^o pelvic bone. 

 Air-bladder present. 



A. Both jaws (lictded hy a median stiturc. 



Dorsal aud anal fins many-rayed 2. Xcnopterus, p. 270. 



Dorsal and anal fins very short 3. Tetrodon, p. 271. 



B. Jaic,^ without median suture. 



Nasal tentacle simple, with a pair of lateral openings. Dermal ossifica- 

 tions ■vs'itli a stiff hut moveable spine .... 4. Uiodon, p. 306. 



Nasal tentacle simple, with a pair of lateral openings. Most of the der- 

 mal ossifications three-rooted, with a stiff" inunoveahlo spine. 



5. Cliihmn/cterus, p. 309. 



Nasal tentacle with two cylindrical and tapering branclies ; no nostril. 

 Posterior dermal ossiticatious three-rooted, with a stirt' immoveahle 

 spine l). I)iroti//ic/it/n/s, p. 314. 



Nasal tentacle as in Dicoti/!ic/ithj/s. All dermal ossilii-aliuns with stiff 

 moveable spines 7. Atupomijctcrus, p. 315. 



A nasal tentacle. Dermal ossifications very small, two-rooted, with a 

 tine flexible spine 8. I'richodiodon, p. 310, 



No nasal tentacle. Dodj' covered with long hair-like bristles. 



9. Trivhocyclus, p. 310. 



Third Group. Molhia. 

 Bod)i compressed, very short, not extensible by air ; fail c.vtremely 



