Body compressed, deep, scaly. Lateral line none. Dorsal and anal fins long, both with numerous spines, the spinous portion being the more developed. Ventrals thoracic, with one spine and five soft rays. Teeth feeble. Pseudobranchiæ hidden.
Only two genera, each represented by one or two species in the Atlantic rivers of Tropical America, Polycentrus and Monocirrhus, belong to this family. They are small insectivorous fishes.
Tenth Family—Teuthididæ.
Body oblong, strongly compressed, covered with very small scales. Lateral line continuous. Eye lateral, of moderate size. A single series of cutting incisors in each jaw; palate toothless. One dorsal fin, the spinous portion being the more developed; anal with seven spines. Ventral fins thoracic, with an outer and an inner spine, and with three soft rays between.
This family consists of one very natural genus, Teuthis, readily recognised by the singular structure of the fins. In all the species the fin-formula is D. 13/10. A. 7/9. The incisors are small, narrow, and provided with a serrated edge. The air-bladder is large, and forked anteriorly as well as posteriorly. Their skeleton shows several peculiarities: the number of vertebræ is twenty-three, ten of which belong to the abdominal portion. The abdominal cavity is surrounded by a complete ring of bones, the second piece of the coracoid being exceedingly long, and extending along the whole length of the abdomen, where it is joined to a spinous process of the first interhæmal. The pubic bones are slender, long, firmly attached to each other, without leaving a free space between them. They are fastened by a long process which passes the symphysis of the radii, and extends on to that of the humeri.
Fig. 182.—Teuthis nebulosa, Indian Ocean.
Thirty species are known, all from the Indo-Pacific; but they do not extend eastwards beyond 140° long., or to the Sandwich Islands. They are herbivorous, and do not exceed a length of fifteen inches.
Second Division—Acanthopterygii Beryciformes.
Body compressed, oblong, or elevated; head with large muciferous cavities which are covered with a thin skin. Ventral fins thoracic, with one spine and more than five soft rays (in Monocentris with two only).