210 THE VOYAGE OF H.M.S. CHALLENGER. 



Dicymba diphyopsis, n. sp. (PL XVIII. figs. 1-7). 



Habitat. — Indian Ocean, between Aden and Bombay, November 1881 (Haeckel). 



Nectosome (fig. 1). — The swimming apparatus is composed of a small pneumatopbore 

 placed at the top of the stem, and of two large opposite nectophores beyond it. These 

 are slightly different in size, and rather similar to the nectocalyces of Praya (PI. XXXI.) 

 in form, structure, and arrangement, so fitting one into another, that the two longitudinal 

 ventral wings of the larger embrace the opposite wings of the smaller swimming-bell. 

 The subcylindrical hydrcecial canal, formed by the two longitudinal ventral grooves, is 

 traversed by the apical part of the trunk, and embraces a great part of the retracted 

 siphosome. This attains in the fully expanded state a length of about half a metre. 



Pneamatophore. — The float is a pyriform vesicle of 10 mm. in length and 6 mm. in 

 breadth. Its apical part is covered with red pigment (fig. l,p). The pneumatosac is a 

 simple invagination of the exoderm of the stem-top, and not connected with the sur- 

 rounding pneumatocodon by radial septa (compare above, p. 206). 



Nectophores. — The two opposite nectophores are of equal form, but a little different 

 in size, 40 mm. to 50 mm. long, 25 mm. to 30 mm. broad. Their form is ovate, with 

 rounded apex and truncate base. The dorsal or abaxial side is evenly convex, without 

 edges, but with a number of flat roundish tubercles, which bear white patches composed 

 of cnidocysts. The ventral or axial side is concave, with a broad longitudinal groove 

 bounded by two prominent lateral wings. In the upper third of the groove, midway 

 between the two wings, arises a short, obliquely triangular lamella, the pedicle of the 

 nectophore. The apex of this triangular pedicle is inserted near the apex of the trunk, 

 somewhat below the base of the pneumatophore. The larger nectophore embraces by its 

 ventral groove the opposite groove of the smaller in the same way as is described above 

 in the case of Praya galea (PI. XXXI. figs. 1-7 . 



Nectosac. — The umbrellar cavity occupies about two-thirds of the nectophore, and is 

 subspherical in the larger proximal half, subcylindrical in the smaller distal half. The 

 opening of the latter is surrounded by a broad velum (fig. 1, v). The muscle-plate of the 

 subumbrella is strong. The nectocalycinc duct arising near the top of the stem, passes 

 downwards through the pedicle of the nectophore and ends in the upper third of the 

 dorsal median line of the subumbrella. It divides here into four radial canals of very 

 different lengths ; the ventral is about half as long as the dorsal, and both are shorter 

 than the two paired lateral canals (right and left) ; these are four times curved in different 

 directions and form the four loops figured in fig. 1, n. All four canals inosculate in the 

 circular canal of the umbrella margin at equal distances. 



Siphosome. — The long and thin tubular trunk of the siphosome had in the single 

 specimen observed, in the fully expanded state, a length of 40 to 60 cm. It bore (besides 



