REMARKS.—In the preceding diagnosis I have followed the arrangement of specific characters adopted by Gill in his description of two new species of _Exocœtus_ from the Pacific Coast of Central America. (Proc. Acad. Phil., June, 1863, p. 167.) By comparison it will be seen that our species is very distinct. This large species of Flying-Fish is found in great numbers during the summer south of Point Conception, and some wander as far north as Santa Cruz at least. They can only be taken when they happen to alight on board of a vessel or in gill-nets, which I was not provided with during my late voyage among the islands. Their flight is rarely higher than ten feet above the water, but sometimes extends nearly a quarter of a mile. UROLOPHUS, Müller and Henle. UROLOPHUS HALLERI, Cooper, State collection, species 522. [FIG. 21.] [Illustration: FIG. 21.] _Specific characters._—Disk suborbicular, obtusely pointed in front, and with the pectoral fins rounded behind. Length anterior to anus a little greater than that of the tail behind it. Posterior outline of ventral fins projecting a little behind that of disk. Claspers as long as ventrals and projecting entirely behind them. Tail 0·47 of total length, gradually tapering from a cylindrical base to the spine, thence becoming flattened laterally expanding into a fin, which commences opposite the base of spine below, and ends opposite to its end above, broadest near its end, where its width is 0·10 the length of tail. Spiracles a little larger than orbits and farther apart, the distance between them equal to that from snout to orbits. Ventrals forming nearly equilateral triangles, their basal length one fifth that of head and body. Caudal spine arising at 0·48 of the length of tail, and not quite one third as long. Female more elongated than male but tail and spine shorter; the ventrals a fourth longer and more acute. _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.