Colors.—Reddish speckled with yellow, below white. In some specimens the dark and light colors above are about equally distributed, the spots having a somewhat marbled arrangement. In others the light spots are very few and widely separated. Popular name “Round Stingray.” The figure is half the natural size. The dots show the principal outlines of the cartilaginous skeleton.
Remarks.—While this fish has the nearly orbicular outline of Urotrygon (mundus), Gill, from Panama (Proc. Phil. Acad., June, 1863, p. 173), it differs generically in having obtusely triangular teeth (equilateral), tail shorter than body, spine nearest to its base, smooth skin, etc.
It differs from Urolophus, as described by Richardson, in the upper velum of mouth being entire, and in having about twenty small tubercles on the surface of lower velum. These however can scarcely be considered generic differences.
Found abundantly in muddy creeks at San Pedro and San Diego, those from the former place being more uniform in color.
While I was at San Diego the little son of Major G. O. Haller, U. S. A. was wounded in the foot, probably by one of these fish, while wading along a muddy shore of the bay. The wound was very painful for some hours, though small. Another large rhomboidal species also abundant there but apparently still undescribed, inflicts very severe and dangerous wounds, of which I may have more to say hereafter.
This fish has great muscular power and can dart very rapidly through the water by lateral vibrations of its tail, at the same time quickly flapping the edge of its disk, to keep its level in the water and to regulate its direction.
It frequently buries itself slightly under the mud, and if disturbed obscures the water by stirring the mud, vanishing in the cloud thus raised to hide itself again. It will allow a boat to pass over its place of concealment, and may, if detected, be easily killed by a blow with the end of an oar. Many are also caught in the seines of the fishermen.
Their food consists of small mollusca, crustacea and such other animals, alive or dead, as they can obtain.