The three suborders of plectognathous are easily recognized by external characters. In the _Sclerodermi_ (σκλερός, hard; δέρμα, skin) the spinous dorsal is present and the body is more or less distinctly scaly. The teeth are separate and incisor-like and the form is compressed. In the _Ostracodermi_ (ὀστράκος, a box; δέρμα, skin) there is no spinous dorsal, the teeth are slender, and the body is inclosed in an immovable, bony box. In the _Gymnodontes_ (γυμνός, naked; ὀδούς, tooth) the teeth are fused into a beak like that of a turtle, either continuous 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, _Triacanthidæ_ 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 hollardi_ in Cuba. _Triacanthus brevirostris_, with the first spine very large, is the common hornfish of the East Indies ranging northward to Japan. [Illustration: FIG. 345.—The Trigger-fish, _Balistes carolinensis_ Gmelin. New York. ] =The Trigger-fishes: Balistidæ.=—The _Balistidæ_, or trigger-fishes, have the body covered with large rough scales regularly arranged. 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 peculiarity gives the name of trigger-fish as well as the older name of _Balistes_, or cross-bow shooter. There are no ventral fins, the long pelvis ending in a single blunt spine. The numerous species of trigger-fishes are large coarse fishes of the tropical seas occasionally ranging northward. The center of distribution is in the East Indies, where many of the species are most fantastically marked. _Balistes carolinensis_, the leather-jacket, or cucuyo, is found in the Mediterranean as also on the American coast. _Balistes vetula_, the oldwife, oldwench, or cochino, marked with blue, is common in the West Indies, as are several other species, as _Canthidermis sufflamen_, the sobaco, and the jet-black _Melichthys piceus_, the black oldwife, or galafata. Several species occur on the Pacific Coast of Mexico, the Pez Puerco, _Balistes verres_, being commonest. Still others are abundant about the Hawaiian Islands and Japan. The genus _Balistapus_, having spinous plates on the tail, contains the largest number of species, these being at the same time the smallest in size and the most oddly colored. _Balistapus aculeatus_ and _Balistapus undulatus_ are common through Polynesia to Japan. Most of the tropical species of _Balistidæ_ are more or less poisonous, causing ciguatera, the offensive alkaloids becoming weaker in the northern species.