Series Plectognathi 623 
more or less distinctly scaly. The teeth are separate and 
incisor-like and the form is compressed. In the Ostracodermi 
(60tpaxos, abox; dépua, skin) there is no spinous dorsal, the teeth 
are slender, and the body is inclosed in an immovable, bony 
box. In the Gymnodontes (yvurvos, naked; déovs, tooth) the 
teeth are fused into a beak like that of a turtle, either con- 
tinuous or divided by a median suture in each jaw, the spinous 
dorsal is lost, and the body is covered with thorns or prickles 
or else is naked. 
The Scleroderms.—The Sclerodermi include three recent and 
one extinct families. Of the recent forms, Triacanthide is 
the most primitive, having the ventral fins each represented 
by a stout spine and the skin covered with small, rough scales. 
The dorsal has from four to six stiff spines. 
Triacanthodes anomalus is found in Japan, Hollardia hol- 
lardi in Cuba. Triacanthus brevirostris, with the first spine very 
large, is the common hornfish of the East Indies ranging north- 
ward to Japan. 
The Trigger-fishes: Balistide.—The Balistide, or trigger-fishes, 
have the body covered with large rough scales regularly arranged. 
Fig. 514.—The Trigger-fish, Balistes carolinensis Gmelin. New York. 
The first dorsal fin is composed of a short stout rough spine, 
with a smaller one behind it and usually a third so placed that 
by touching it the first spine may be set or released. This 
