The smaller species have usually shorter fins and approach more nearly to the halfbeaks. Fodiator acutus, with sharp jaws, and Hemiexocœtus, with a short beak on the lower jaw, are especially intermediate. The flight of the flying-fishes is described in detail on p. 157, Vol. I.
The Catalina flying-fish, Cypselurus californicus, of the shore of southern California is perhaps the largest of the known species, reaching a length of 18 inches. To this genus, Cypselurus, having a long dorsal and short anal, and with ventrals enlarged as well as pectorals, belong all the species strongest in flight, Cypselurus heterurus and furcatus of the Atlantic, Cypselurus simus of Hawaii and Cypselurus agoo in Japan. The very young of most of these species have a long barbel at the chin which is lost with age.
In the genus Exonautes the base of anal fin is long, as long as that of the dorsal. The species of this group, also strong in flight, are widely distributed. Most of the European flying-fishes, as Exonautes rondeleti, Exonautes speculiger, and Exonautes vinciguerræ, belong to this group, while those of Cypselurus mostly inhabit the Pacific. The large Australian species Exonautes unicolor, Fig. 226, Vol. I, belongs to this group. In the restricted genus Exocœtus the ventral fins are short and not used in flight. Exocœtus volitans (evolans) is a small flying-fish, with short ventral fins not used for flight. It is perhaps the most widely distributed of all, ranging through almost all warm seas. Parexocœtus brachypterus, still smaller, and with shorter, grasshopper-like wings, is also very widely distributed. An excellent account of the flying-fishes of the world has been given by Dr. C. F. Lütken (1876), the University of Copenhagen, which institution has received a remarkably fine series from trading-ships returning to that port. Later accounts have been given by Jordan and Meek, and by Jordan and Evermann.
Fig. 169.—Catalina Flying-fish, Cypselurus californicus (Cooper). Santa Barbara.
Very few fossil Exocœtidæ are found. Species of Scombresox and Hemirhamphus are found in the Tertiary, the earliest being Hemirhamphus edwardsi from the Eocene of Monte Bolca. No fossil flying-fishes are known, and the genera, Exocœtus, Exonautes, and Cypselurus are doubtless all of very recent origin.
CHAPTER XII
PERCESOCES AND RHEGNOPTERI
Suborder Percesoces.—In the line of direct ascending transition from the Haplomi and Synentognathi, the pike and flying-fish, towards the typical perch-like forms, we find a number of families, perch-like in essential regards but having the ventral fins abdominal.
These types, represented by the mullet, the silverside, and the barracuda, have been segregated by Cope as an order called Percesoces (Perca, perch; Esox, pike), a name which correctly describes their real affinities. In these typical forms, mullet, silverside, and barracuda, the affinities are plain, but in other transitional forms, as the threadfin and the stickleback, the relationships are less clear. Cope adds to the series of Percesoces the Ophiocephalidæ, which Gill leaves with the Anabantidæ among the spiny-rayed forms. Boulenger adds also the sand-lances (Ammodytidæ) and the threadfins (Polynemidæ), while Woodward places here the Crossognathidæ. In the present work we define the Percesoces so as to include all spiny-rayed fishes in which the ventral fins are naturally abdominal, excepting those having a reduced number of gill-bones, or of actinosts, or other peculiarities of the shoulder-girdle. The Ammodytidæ have no real affinities with the Percesoces. The Crossognathidæ and other families with abdominal ventrals and the dorsal spines wholly obsolete may belong with the Haplomi. Boulenger places the Chiasmodontidæ, the Stromateidæ, and the Tetragonuridæ among the Percesoces, an arrangement of very doubtful validity. In most of the Percesoces the scales are cycloid, the spinous dorsal forms a short separate fin, and in all the air-duct is wanting.