Tetragonurus
in ichthyology, a genus of Atherinidæ, with a single species. Body sub-elongate, scales strongly the second. It is a rare fish, more frequently met with in the Mediterranean than in the Atlantic. Nothing is known of its habits, but as, when young, it accompanies the Meduse, it must be regarded as a pelagic form. At a later period of its existence it probably descends to greater depths, coming to the surface only at night. It attains a length of about 18 inches.