19. TETRAG0N0PTEKUS. 317 



19. TETRAGONOPTERUS* 



Tetragonopterus, Cuv. Mem. Mus. 1818, iv. p. 455 (not Tetragono- 

 ptrus, Klein) f. 



The dorsal fin is placed in the middle of the length of the body, 

 above or immediately behind the ventrals ; anal fin long. Body 

 oblong or elevated, covered with scales of moderate size ; belly 

 rounded. Cleft of the mouth of moderate width. Anterior teeth 

 strong, lateral teeth small. Intermaxillary and mandibulary teeth 

 subequal in size, with a compressed and notched crown, the former 

 in a double, the latter in a single series ; maxillary with a few teeth 

 near its articulation, rarely with the entire edge denticulated. The 

 intermaxillary has no lateral process overlapping a part of the front 

 of the maxillary. Nostrils close together, separated by a valve only. 

 Gill-opening wide, the gill-membranes being free from the isthmus 

 and separate. Gill-rakers setiform. 



Tropical America. 



The numerous species of this genus may be subdivided as follows : — 



A. Anal rays forty or more. 



a. Maxillary with only a few rudimentary teeth near its articula- 



tion, p. 318. 



b. The entire edge of the maxillary denticulated, p. 319. 



B. Anal rays less than forty. 



a. Cleft of the mouth of moderate width ; maxillary without teeth 

 along its edge, extending to, or not much beyond, the front margin 

 of the eye. 



a. The height of the body is one-half, or more than one-half, of the 

 total length (without caudal), p. 319. 



* 1. Tetragonopterus orbignyanus, Cuv. $ Val. xxii. p. 147. — Buenos Ayres. 



2. viejita, Cuv. $ Vol. xxii. p. 154. — Lake of Maracaibo. 



3. sawa, Casteln. Anim. Amir. Sud, Poiss. p. 65. pi. 33. fig. 1.— Rio 



Crixas. 



4. mexicanus, Filippi, in Gver.Bev. et Mag. Zool. 1853, p. 166. — Mexico. 



5. Pcecilurichtbys brevoortii, Gill, Ann. Lye. Nat. Hist. New York, 1858, 



p. 417.— Trinidad. 



6. taeniurus, Gill, I. c. p. 418. — Trinidad. 



7. pulcher, Gill, I. c. p. 419. — Trinidad. — In the descriptions of the 



three last-named species it is not stated whether the origin of the dorsal 

 fin is behind, or opposite to, that of the ventral. 



8. Pcecilurichthys (Hemigrammus) unilineatus, Gill, I. c. p. 420. — Trinidad. 



— Lateral line discontinued in the middle of the body. A. 27; 

 t Klein formed the name of Tetragonoptrus for fishes of the Linnean genus 

 Tetrodon, giving at the same time an etymological explanation of the word. 

 Artedi afterwards referred a South American Characinoid to the Kleinian genus, 

 preserving the original and correct spelling. Cuvier, taking Artedi's species as 

 the type of the genus, adopted the name erroneously used by Artedi, but, mis- 

 understanding the derivation of the word, wrote Tetragonopterus. In spite of 

 the similarity of the two words, their meaning is sufficiently distinct to forbid the 

 introduction of a new generic name, and the preservation of Tetragonopterus 

 must be thfi more recommended as it is in common use, whilst Tetragonoptrus 

 will probably for ever remain a synonym. 



