REPORT ON THE DEEP-SEA MEDUSAE. 17 



cups into eight to twelve radial cords, which converge towards the centre of the suck- 

 ing-cup (figs. 9, 10). 



The auditory clubs (probably eight or sixteen) lie on the axial side of the umbrella 

 margin, under the insertion of the velum, inside the lowest row of tentacles. After most 

 careful search, I was only able to discover two or three of them, very small, and of the 

 same construction as in the Aglauridse. The thin endodermal axis of the auditory club 

 (fig. 16) consists of a few chordal cells ((/), of which the last is expanded like a vesicle, 

 and contains a large spheroidal otolith with concentric layers (ol). The ectodermal cells 

 of the epithelium of the club bear very long and fine auditory hairs (oh). 



The velum (figs. 11-14) is thicker in Pedis than in any Craspedote hitherto known, 

 and is distinguished by a very unusual development of the muscular system. The breadth 

 of the velum is so great that when fully extended it can probably close the entire 

 umbrella cavity like a sphincter. The external abaxial half of the velum contiguous to 

 the umbrella margin, is nearly as thick as the tentacles, and three to six times as thick 

 as the internal axial half, from which it is divided by a deep circular furrow (fig. 11, 

 right half). If we draw the free projecting internal margin of the velum carefully 

 towards the inside, we can bring it so near the centre as to make it probable that the 

 umbrella cavity can be completely closed by the velum being drawn over it, as in the 

 foregoing species. The following layers (from above to below in the natural position of 

 the horizontal extended velum) can be distinguished in horizontal sections through the 

 velum : — (l) the ventral or subumbral epithelium of the velum (viv), containing dark- 

 brown pigment similar to that of the subumbral epithelium ; (2) a considerably thick 

 layer of clear vesicular connective tissue (x) ; (3) the muscular plate of the velum which 

 projects into this connective tissue in the form of numerous highly-developed circular 

 folds, each fold sending out numerous secondary folds or shoots into the clear plate of 

 connective substance (x), so that it appears delicately pinnated in the transverse section 

 (fig. 13, mv) ; (4) a thin but firm elastic supporting lamella, which sends out processes 

 into the muscular folds (zv); (5) the dorsal or exumbral epithelium of the velum (ve). 

 The epithelial cells of the exumbral epithelium of the velum are much smaller and 

 flatter than those of the subumbral. 



The ectodermal epithelium of the lower surface of the umbrella or the subumbrella 

 consists of cells of dark brown pigment, from which the milk-white walls of the canals 

 are sharply thrown out. The underlying annular system of the subumbrella forms 

 numerous compact circular folds. In Pedis the umbrella cavity is simple, without 

 subumbral funnel cavities, as the eight radial " mesogonia " or " genital mesenteries " 

 so strongly developed in Pedyllis and Pectanthis are by no means so complete here. 

 They are merely indicated by eight narrow subumbral folds, running from the basis of 

 the eight genitalia to the basis of the stomach (fig. 2, wr). 



The gastrovascular system in Pedis has, on the whole, the same plan as that of 



(ZOOL. CHALL. EXP. PART XII. 1881.) M 3 



