MEDUSAE. I. 



blance to that of Chromatoncma rubrum. The largest specimens have as much as about 64 tentacles; 

 the tentacle bulbs have exactly the same shape as in Chromatonema rubrum (op. cit. Plate 39, fig. 5). 

 According to the description Bige low's species possesses both cirri and cordyli. Only a few cirri 

 were present in his specimens; they are cylindrical and provided with a cluster of nematocysts in the 

 distal end. The cordyli are spindle-shaped and carry no nematocysts. One or two cordyli are .present 

 between every two successive tentacles. As mentioned above the cordyli of Chromatonema rubrum may- 

 be cylindrical or more or less spindle-shaped, in both cases provided with nematocysts, and they are 

 situated in a manner very similar to the arrangement of the cordyli described by Bige low. The 

 "cordyli" of "Ptychogena erythrogonon" are undoubtedly homologous with the cordyli of Chromatonema 

 rubrum; as to the homologies of the "cirri" of the former I am not quite sure; the drawing of a single 

 "cirrus" (Plate 38, fig. 9) recalls the cylindrical form of cordyli in Chromatonema rubrum, only a little 

 more lengthened and somewhat more heavily armoured with nematocysts; in fig. 5 of Plate 39, however, 

 the name of "cirrus" is attached to an organ which is undoubtedly a young tentacle. 



As in Chromatonema rubrum, the base of the mauubrium of " Ptychogena erythrogonon" is qua- 

 drate and attached to the subumbrella along the arms of a perradial cross. The mouth-tube is said to 

 be barrel-shaped, while I have described it as being quadrangular in Chromatonema rubrum-' but it is 

 very likely, that the mouth-tube of the last-named species may attain a circular outline when fully 

 expanded; such is the case in several other species, in which the stomach is quadrate when not ex- 

 panded. The shape of the radial canals and the gonads of "Ptychogena erythrogonon^ is exactly as in 

 Chromatonema rubrum, the radial canals having "developed a series of short lateral diverticula along 

 the narrow lines by which they are attached to the subumbrella (Plate 39, fig. 2). The main bodies of 

 the canals, however, are so stout that they extend out as far as the ends of these short branches. The 

 gonads develop in the spaces between the diverticula, and are confined to the aboral surfaces of the 

 canals close to the subumbrella ..." (op. cit. p. 151). The distal narrow part of the radial canal is 

 shorter in "Ptychogena erythrogonon" than in Chromatonema rubrum. - The colour seems to be the 

 same in both species. - The two species are undoubtedly nearly related and must be referred to the 

 same genus. In fact, I can see no other noticeable differences than the want of nematocysts in the 

 cordyli of the Pacific species, and the size, Chromatonema rubrum reaching maturity when about 20 

 24 mm in diameter with about 2024 tentacles, whereas Chromatonema erythrogonon grows to a larger 

 size and may possess 64 tentacles when fully developed. 



Another similar form is described by Vanhoffen (1911) as Ptychogena Hcrtwigi, found in the 

 Indian Ocean by the German deep-sea expedition. Vanhoffen describes his species as very like 

 Ptychogena erythrogonon Bigelow, but still larger, 50 mm in diameter, yet with a smaller number of 

 tentacles, viz. 20. It has no cordyli but 5 cirri between each successive pair of tentacles. The "cirri", 

 as shown in the figure in the text, seem to be partly cylindrical, partly somewhat club-shaped, partly 

 spindle-shaped. According to the coloured figure (Taf. XXII, Fig. 9) the gonads reach only to the 

 middle of the radial canals. Also this species is undoubtedly nearly related to Chromatonema rubrum 

 Fewkes and belongs to the same genus. 



Further investigations will show whether the three species mentioned are distinct or only local 

 varieties of one and the same species, viz. Chromatoncma rubrum Fewkes. 



