396 FISHES. PLECTOGNATHI. 



sal fin with one large spine and three or four smaller ones ; 

 skin covered with small crowded scales ; eight teeth in each 

 jaw ; tail elongated. 



T. biaculeatus, Cuv. Body elongated, dusky on the upper parts, 

 whitish on the sides and abdomen ; snout elongated ; first ray of the 

 first dorsal fin much longer than the others ; ventral spines lon- 

 and pointed ; tail forked. 6 to 8 inches long. Inhabits Indian 

 seas.- Shaw, v. pi. 169. 



Gen. 8. OSTRACION, Lin. 



Head and body covered with osseous plates ; jaws armed with 

 ten or twelve conical teeth ; destitute of the bones of the pel- 

 vis and ventral fins ; branchial openings with a cutaneous 

 lobe, but having within an operculum with six rays ; one 

 dorsal and one anal fin. 



The fishes of this genus have the bony plates by which they are covered fixed into 

 an inflexible shield, in such a manner that the tail, fins, mouth, and the lobes of the 

 branchiae are alone moveable. The greater number of the vertebras are also fixed. 

 Cuvier proposes the division of the genus according to the form of the body and 

 the spines ; but the differences in this respect, which may be only sexual, have not 

 been well ascertained. 



1. Body triangular, without spines. 



O. triqueter, Bloch. Triangular Trunk- Fish. Body reddish-brown, 

 with a white spot in the centre of each hexagonal space ; sides 

 sloping obliquely from the ridge of the back ; abdomen flat ; fins 

 yellowish; tail rounded. 12 inches long. Inhabits Indian and 

 American seas. Bloch, pi. 130. 



O. concatenates, Bloch. Plates of the body of various shapes, but 

 in a reticulated order ; colour brown, the dividing lines pale rose- 

 coloured ; sides violet or grayish ; belly white ; tail fins reddish- 

 brown. Inhabits American seas Bloch, pi. 131. 



2. Body triangular, with spines behind the abdomen. 



O. bicaudalis, Bloch. Body marbled with gray and pale yellow, 

 with numerous small round black spots ; two spines near the anus. 

 Inhabits Indian seas. Shaw, v. pi. 170. 



O. trigonus, Bloch. Back very convex ; head thick and truncated ; 

 opening of the mouth small ; plates hexagonal, with numerous 

 small tubercles ; colour brownish-yellow ; fins yellow, with a blu- 

 ish border ; two subcaudal striated spines. 1 foot long. Inha- 

 bits South American seas Bloch, pi. 135. 



3. Body triangular, with two frontal and two subcaudal spines. 



O. quadricornis, Bloch. Body subtrigonal, very convex above; plates 

 of the body in large hexagons, and marked with numerous and 

 very small tubercles ; two strong spines on the top of the head 

 pointing forwards, and two before the anal fin pointing back- 

 wards ; colbur deep brown, with elongated spots ; tail and fins 



