378 DESCRIPTION OF A SILURUS. 
considerable firmness, which sends off two posterior appen- 
dages toward the upper part of the branchial apertures. 
The middle of its posterior margin is notched, to receis^e 
the apex of a very strong heart-shaped bone, the lobes of 
which reach the base of the dorsal fin. This shield or plate 
is rough with bony granulations, of a larger size than those 
of the armour on the head, and is obtusely carinated to- 
wards its posterior part. 
The head is very broad ; the mouth is wide, terminal, 
and furnished with numerous minute teeth, which are ra- 
ther intended for holding fast, than biting the prey of the 
animal. These teeth are thickly planted on the edges of 
the mouth, in such a manner as to resemble the hairs of a 
very stiff brush. They are arranged in two groups about 
half an inch wide, on each jaw, reaching along the whole 
aperture of the mouth, and are divided in front by a slight 
furrow. Two convex, oblong bones of considerable size, 
and furnished with similar teeth, form the osseous palate of 
this fish. The eyes are small, placed rather above the line 
of the mouth, and more than an inch and a half from its 
angles. There are six tentacula or cirri on the lips. The 
longest pair are on the upper jaw, very near the angles of 
the mouth, and measure full 8 inches in length. The next 
pair are more than an inch below the lower jaw-bone, and 
measure 4| inches. The shorter pair are placed near the 
middle of the lower jaw, and measure 2J inches. 
The first ray of pectoral and first dorsal fins consists of a 
very strong and slightly incurvated bony spine, with a 
rough granular surface, and a serrated concave edge. The 
sharp apices of these spines form powerful weapons of 
offence and defence for the naked body of the fish. The 
pectoral spine is a little more curved than that of the dor- 
sal fin. All these spines are moveable, apparently by means 
of strong muscles. The length of the dorsal spine is 6J 
