As may be seen from the above, C. Xaymacana differs only a little from the C. marsupialis of the Mediterranean. Claus mentions in the latter a more or less well defined asymmetry of the bell, which he connects with a supposed occasional attachment by the proboscis to algæ. In C. Xaymacana I never noticed but that the bell was perfectly symmetrical. C. Xaymacana is about two-thirds the size given by Claus for his examples of C. marsupialis, which were not then sexually mature. It has 16 velar canals instead of 24 (32), as given by Haeckel, or 24 as figured by Claus. Difference in size and in number of velar canals are essentially the characteristics upon which Haeckel founded his Challenger species, C. Murrayana. Family II: CHIRODROPIDÆ (Haeckel, 1877). Cubomedusæ with four interradial groups of tentacles; with sixteen marginal pockets in the marginal lobes of the velarium, and with eight pocket arms, belonging to the exumbrella, in the four stomach pockets. This family is represented in American waters by a species of Chiropsalmus, identified by H. V. Wilson as C. quadrumanus, found at Beaufort, North Carolina. Family III: TRIPEDALIDÆ (1897). Cubomedusæ with four interradial groups of tentacles, each group having three tentacles carried by three distinct pedalia; without marginal lobes in the velarium; with sixteen marginal pockets; without pocket arms in the stomach pockets. Genus: _Tripedalia_. For the present the characteristics of family and genus must necessarily be for the most part the same. The genus is distinguished by having twelve tentacles in four interradial groups of three each; velarium suspended by four perradial frenula; canals in the velarium; stomach projecting somewhat convexly into the bell cavity, with relatively well-developed suspensoria; four horizontal groups of gastric filaments, each group brush-shaped, limited to the interradial corners of the stomach. Species: _Tripedalia cystophora_ (Fig. 17).