REPORT ON THE DEEP-SEA MEDUSAE. 105 



we can distinguish sixteen pairs of longitudinal lobe muscles, a pair for each marginal 

 lobe. 



From the umbrella being so much vaulted, the umbrella cavity (w) is more spacious 

 and higher than in most other Discomedusae. It is nearly cylindrical in form, as its 

 subumbral side walls rise nearly perpendicular (fig. 14). But as the eight genitalia 

 project like arches towards the inside, it is rather octangularly prismatic. Its upper 

 base is occupied by the subumbral bottom of the stomach (gw), its lower bases by the 

 wide opening of the umbrella, surrounded by the corona or marginal lobes. The axial 

 middle space of the proximal half is filled by the pendant oesophagus. The 

 subumbral gastral wall forms four narrow mesenteric folds or mesogonia in a radial 

 direction above, and projects further between them iD an interradial direction, so as to 

 form four flat, interradial funnel cavities (fig. 3, ii) ; these are covered over by the four 

 flat pyloric valves (fig. 2, gi), which bear the phacellse (fig. 2, f). The special 

 formation of this part is very similar to that of many Cubomedusse (Charybdeidae). 



In Nauphanta, as in Ephyra, the common ancestral form of all Discomedusse, and in 

 most genera of the family Ephyridas (all Palephyridse and Nausithoidea), the umbrella 

 margin (PI. XXVII. fig. 1; PL XXVIII. figs. 12-14) is regularly composed of the 

 following marginal organs : — Eight rhopalia (four perradial and four interradial), eight 

 adradial tentacles alternating with these, and sixteen subradial marginal lobes, inserted 

 between the rhopalia and the tentacles. The number of the sixteen marginal organs, 

 which alternate with the sixteen subradial marginal lobes, is therefore the same here as 

 in Tesseranbha (PI. XV.) and Periphylla (PI. XVIII. &c). Whilst, however, in the 

 Stauromedusa Tesserantha all the sixteen marginal organs remain simple tentacles, and 

 in the Peromedusa Periphylla the four interradial tentacles are transformed into 

 rhopalia, in our Ephyrida only the eight adradial tentacles appear to be permanent ; 

 the eight principal tentacles (four perradial and four interradial) are transformed into 

 the characteristic sense clubs, as in all other Disconiedusse. 



The eight sense clubs or rhopalia (figs. 12, 13, c?',-fig. 20) resemble most strongly 

 those of the most closely allied Nausiihoe, among all known forms of these organs, 

 though they also agree in many and most important points with those of Periphylla 

 (PL XVIIL). They are distinguished from those of most other Discomedusae by their 

 broad, succinct shape. The eight sense clubs lie hidden between each pair of marginal 

 lobes in four perradial and four interradial deep incisions of the umbrella margin, which 

 alternate with the deep tentacular incisions (figs. 12-14). Each rhopalium has, on the 

 whole, the form of a broad tongue-shaped leaf, and is nearly one and a half times as long 

 as broad. In the normal position of the vertical umbrella margin, its free distal end is 

 directed upwards in such a way that the convex abaxial surface looks freely outwards, 

 the concave axial surface freely inwards towards the umbrella cavity. Of the four sense 

 organs which are united in each rhopalium, the olfactory depression lies on the convex 



(ZOOL. CIIALL. EXP. PART XII. 1881.) M 14 



