=The Porcupine-fishes: Diodontidæ.=—In the remaining families of _Gymnodontes_, there is no suture in either jaw, the teeth forming an undivided beak. The _Diodontidæ_, or porcupine-fishes, have the body spherical or squarish, and armed with sharp thorns, the bases of which are so broad as to form a continuous coat of mail. In some of them, part of the spines are movable, these being usually two-rooted; in others, all are immovable and three-rooted. All are reputed poisonous, especially in the equatorial seas. In _Diodon_ the spines are very long, the anterior ones, at least, movable. The common porcupine-fish, _Diodon hystrix_, is found in all seas, and often in abundance. It is a sluggish fish, olive and spotted with black. It reaches a length of two feet or more, and by its long spines it is thoroughly protected from all enemies. A second species, equally common, is the lesser porcupine-fish, _Diodon holacanthus_. In this species, the frontal spines are longer than those behind the pectoral, instead of the reverse, as in _Diodon hystrix_. Many species of _Diodon_ are recorded from the Eocene, besides numerous species from later deposits. One of these, as _Heptadiodon heptadiodon_ from the Eocene of Italy, with the teeth subdivided, possibly represents a distinct family. _Diodon erinaceus_ is found in the Eocene of Monte Bolca and _Progymnodon hilgendorfi_ in the Eocene of Egypt. [Illustration: FIG. 362.—Rabbit-fish, _Chilomycterus schœpfi_ (Walbaum). Noank, Conn. ] In the rabbit-fishes (_Chilomycterus_) the body is box-shaped, covered with triangular spines, much shorter and broader at base than those of _Diodon_. Numerous species are known. _Chilomycterus schœpfi_ is the common rabbit-fish, or swell-toad of our Atlantic coast, light green, prettily varied with black lines. The larger, _Chilomycterus affinis_, with the pectoral fin spotted with black, is widely diffused through the Pacific. It is rather common in Japan, where it is the torabuku, or tiger puffer. It is found also in Hawaii, and it is once recorded by Dr. Eigenmann from San Pedro, California, and once by Snodgrass and Heller, from the Galapagos. =The Head-fishes: Molidæ.=—The headfishes, or _Molidæ_, also called sunfishes, have the body abbreviated behind so that the dorsal, anal, and caudal fins seem to be attached to the posterior outline of the head. This feature, constituting the so-called gephyrocercal tail is a trait of specialized degradation. [Illustration: FIG. 363.—Headfish (adult), _Mola mola_ (Linnæus). Virginia. ]