The species upon which the new family was founded was obtained in great abundance in one locality in Kingston Harbor in the summer of 1896. The environment was even more unlike that in which Cubomedusæ have been found heretofore than in the case of Charybdea Xaymacana. On the west side of the Harbor there is a part more or less cut off from the main body of water, and so from the ocean, by a peninsula. This sheltered bay is dotted with small mangrove islands which toward the head of the bay become so numerous as virtually to convert it into a mangrove swamp. The water is shallow and discolored with organic matter, showing that the tide does not exercise much influence here, and the bottom is for the most part a black mud, deep enough to make wading very uncomfortable but not impossible near shore. The islands rise but slightly above the level of the waters, and the thick vegetation that covers them, for the most part mangroves, grows out into the water on all sides, forming a fringe of overhanging boughs. It was here in the shelter of the boughs, among the roots and half-submerged stems of the mangroves, that the small Cubomedusa was found to thrive. It could be obtained in great abundance almost any day, and of all sizes from the largest adults with stomach pockets filled with eggs or embryos down to small specimens only about two millimeters in diameter. In but one other place was Tripedalia found, and that was a similar region of half landlocked water skirted with mangroves, situated near Port Royal, across the harbor from the locality just mentioned. It would be hard to find places in which the conditions of life were more strikingly different from those of the pure deep sea in which the Cubomedusæ have been generally found before. The slight brownish yellow pigment made the small medusæ a little difficult to see in the discolored water, but like the pellucid Charybdea in the clear water of the harbor, their active movements gave away their presence. The swimming was very vigorous and was effected by quick, strong pulsations (as many as 120 per minute were counted), very different from the slow, rhythmic contractions of the Discomedusan Cassiopea which was found in the same region over by Port Royal. Whether or not the animal made intentional efforts to escape capture could not be decided satisfactorily, but certain it was that they did escape often enough by swimming quickly below the surface of the semi-opaque water.