=The Peristediidæ.=—The _Peristediidæ_ are deep-water sea-robins, much depressed, with flat heads, a bony coat of mail, and two free feelers on the pectoral fin instead of three. The species of _Peristedion_ are occasionally taken with the dredge. _Peristedion cataphractum_ is rather common in Europe. The extinct _Peristedion urcianense_ is described from the Pliocene of Orciano, Tuscany. =The Flying Gurnards: Cephalacanthidæ.=—The flying gurnards, _Cephalacanthidæ_, differ in numerous respects and are among the most fantastic inhabitants of the sea. The head is short and bony, the body covered with firm scales, and the very long, wing-like pectoral fin is divided into two parts, the posterior and larger almost as long as the rest of the body. This fin is beautifully colored with blue and brownish red. The first spine of the dorsal fin is free from the others and more or less prolonged. The few species of flying gurnard are much alike, ranging widely in the tropical seas, and having a slight power of flight. The flying robin, or batfish, called in Spanish volador or murcielago, _Cephalacanthus volitans_, is common on both coasts of the Atlantic, reaching a length of eighteen inches. _Cephalacanthus peterseni_ is found in Japan and _Cephalacanthus orientalis_ in the East Indies, Japan, and Hawaii. The immature fishes have the pectoral fins much shorter than in the adult, and differ in other regards. _Cephalacanthus pliocenicus_ occurs in the Lower Pliocene of Orciano, Tuscany. _Petalopteryx syriacus_, an extinct flying gurnard found in the Cretaceous of Mount Lebanon, is an ally of _Cephalacanthus_. The body is covered with four-angled bony plates, and the first (free) spine of the dorsal is enlarged. CHAPTER XXVI GOBIOIDEI, DISCOCEPHALI, AND TÆNIOSOMI =SUBORDER Gobioidei, the Gobies: Gobiidæ.=—The great family of _Gobiidæ_, having no near relations among the spiny-rayed fishes, may be here treated as forming a distinct suborder. The chief characteristics of the family are the following: The ventral fins are thoracic in position, each having one spine and five soft rays, in some cases reduced to four, but never wanting. The ventral fins are inserted very close together, the inner rays the longest, and in most cases the two fins are completely joined, forming a single roundish fin, which may be used as a sucking-disk in clinging to rocks. The shoulder-girdle is essentially perch-like in form, the cranium is usually depressed, the bones being without serrature. There is no lateral line, the gill-openings are restricted to the sides, and the spinous dorsal is always small, of feeble spines, and is sometimes altogether wanting. There is no bony stay to the preopercle. The small pharyngeals are separate, and the vertebræ usually in normal number, 10 + 14 = 24.