Three species are known, common on the shores of the Tropical Atlantic (F. tabaccaria) and Indian Oceans (F. serrata and F. depressa); they attain to a length of from four to six feet.
The anterior portion of the vertebral column shows the same peculiarity as in Dactylopterus; it is a long compressed tube, composed of four elongate vertebræ, which are perfectly anchylosed; each of them has a pair of small foramina for blood-vessels. The neural spines and parapophyses of this tubiform portion are confluent into thin laminæ, the lateral of which are wing-like, and expanded in their anterior half.
Aulostoma.—Body covered with small scales. Caudal fin rhombic, without prolonged rays; a series of isolated feeble dorsal spines. Teeth rudimentary.
Two species from the Tropical Atlantic and Indian Oceans.
Auliscops.—Body naked. Ventrals thoracic. Numerous spines in front of the dorsal fin.
One species (A. spinescens) from the Pacific coast of North America. Aulorhynchus from the same sea, and Aulichthys from Japan, are allied genera.
Thirteenth Division—Acanthopterygii Centrisciformes.
Two dorsal fins; the spinous short, the soft and the anal of moderate extent. Ventral fins truly abdominal, imperfectly developed.
This division consists of one family, Centriscidæ, with two genera. The fishes belonging to it are very small, marine, and, in consequence of their limited power of swimming, often driven out into the open sea. They have the same structure of the mouth and snout as the Fistulariidæ, but combine with it peculiarities of the shape of body, of the structure of the vertical fins, and of the relations between endo- and exo-skeleton, which render them altogether a singular and interesting type. Amphisile has been found in a fossil state at Monte Bolca.
Centriscus.—Body oblong or elevated, compressed, covered with small rough scales; lateral line none; some bony strips on the side of the back, and on the margin of the thorax and abdomen; the former, in one species, are confluent and form a shield. Teeth none. Two dorsal fins, the first with one of the spines very strong. Ventral fins small, abdominal, composed of five soft rays. Four branchiostegals.