Body more or less elongate, sub-cylindrical, covered with scales of moderate size; lateral line indistinct. Cleft of the mouth of moderate width, with the dentition feeble. Eye lateral, large or of moderate size. Gill-openings wide. Vertebræ very numerous.
Small carnivorous fishes inhabiting the seas of the temperate and tropical zones; many enter fresh water, and some have been entirely acclimatised in it. This family seems to have been represented in the Monte Bolca formation by Mesogaster.
Atherina.—Teeth very small; scales cycloid. The first dorsal is short and entirely separated from the second. Snout obtuse, with the cleft of the mouth straight, oblique, extending to or beyond the anterior margin of the eye.
The Atherines are littoral fishes, living in large shoals, which habit has been retained by the species acclimatised in fresh water. They rarely exceed a length of six inches, but are nevertheless esteemed as food. From their general resemblance to the real Smelt they are often thus misnamed, but may always be readily recognised by their small first spinous dorsal fin. The young, for some time after they are hatched, cling together in dense masses, and in numbers almost incredible. The inhabitants of the Mediterranean coast of France call these newly hatched Atherines “Nonnat” (unborn). Some thirty species are known, of which A. presbyter and A. boyeri occur on the British coast.
Atherinichthys, distinguished from Atherina in having the snout more or less produced; and the cleft of the mouth generally does not extend to the orbit.
These Atherines are especially abundant on the coasts and in the fresh waters of Australia and South America. Of the twenty species known, several attain a length of eighteen inches and a weight of more than a pound. All are highly esteemed as food; but the most celebrated is the “Pesce Rey” of Chile (A. laticlavia).
Tetragonurus.—Body rather elongate, covered with strongly keeled and striated scales. The first dorsal fin is composed of numerous feeble spines, and continued on to the second. Lower jaw elevated, with convex dental margin, and armed with compressed, triangular, rather small teeth, in a single series.
This very remarkable fish is more frequently met with in the Mediterranean than in the Atlantic, but generally scarce. Nothing is known of its habits; when young it is one of the fishes which accompany Medusæ, and, therefore, it must be regarded as a pelagic form. Probably, at a later period of its life, it descends to greater depths, coming to the surface at night only. It grows to a length of eighteen inches.
Third Family—Mugilidæ.
Body more or less oblong and compressed, covered with cycloid scales of moderate size; lateral line none. Cleft of the mouth narrow or of moderate width, without or with feeble teeth. Eye lateral, of moderate size. Gill-opening wide. The anterior dorsal fin composed of four stiff spines. Vertebræ twenty-four.