RErORT ON THE DEEP-SEA MEDUS/E. 33 



The subumbral internal surface is strongly concave, corresponding to this external 

 vaulting, and forms a protecting cavity, which is only open in a radial direction 

 towards the umbrella cavity. We shall designate these cavities, which are essentially 

 niches or secondary cavities of the umbrella cavity, and surround it like the altar niches 

 of a circular temple (Pantheon), the lobe cavities ; in most other Peganthidse (as in the 

 following species Pegantha pantheon) they serve for the reception and protection of the 

 genital sacs, which branch out from the gastral genital ring. The central umbrella cavity 

 itself (fig. 3, h), which is very flat and low as in all Peganthidse, is limited above by the 

 subumbral gastral wall and the genitalia lying in it, whilst it opens wide below (fig. 1). 



The subumbrella is represented in the central part as far as the lower surface of the 

 umbrella lens by the muscular subumbral gastral wall, as this extends to the borders of 

 the lens and collar. In the peripheric part, on the other hand, at the lower surface of 

 the umbrella collar, the subumbrella forms a circle of isolated muscular plates lining the 

 inner concave surface of the lobes. The muscular ring of the subumbrella appears lobed 

 in the lower part, from the proper margin of the umbrella (with the nerve ring and 

 indicating ring), being deeply indented between every second lobe. The velum completely 

 occupies the interspaces between the lobes to the umbrella margin like a swimming mem- 

 brane, and moreover projects internally a little further than the connecting annular margin 

 towards the axis of the umbrella cavity. The velum is very thick and compact, laid in 

 many folds, and, like the lobes, almost always found more or less rolled up. Concentric 

 annular folds predominate in the inner or axial part of the velum, whilst radial folds 

 predominate in the outer or abaxial part, which runs in between the folds in the form 

 of a triangular tip (figs. 6, 8, v). The subumbrella is so deeply indented between 

 each two lobes that the triangular tips of the velum rise between them as far as 

 their base and the insertion of the tentacles (figs. 2, 6). The structure of the sub- 

 umbrella and of the velum is the same as in the next following species (comp. PI. XII. 

 fig. 12). 



As the proper umbrella margin (in a morphological sense) is not determined by the 

 free axial margin of the velum (the limit between exumbrella and subumbrella), but 

 rather by the marginal urticating ring and the double nerve ring lying on it, the true 

 umbrella margin appears deeply indented in Polycolpa forshalii, as in all Peganthidse. 

 It forms a continuous margin of the collar lobes and, at the same time, the frontier line 

 between these and the velum (fig. 6, nc). The festoon canal lies on the inner margin 

 of the urticating ring (fig. 6, cf) which accompanies it all along. The more minute 

 structure of the umbrella margin is the same as in the following species (comp. PI. XII. 

 fig. 12). Of tentacular organs the umbrella margin bears twenty-five tentacles and a 

 large number of auditory clubs (five to seven on each lobe). 



The tentacles, whose number in all Peganthidse ecpials that of the collar lobes, alter- 

 nate regularly with the latter, and are inserted at the bases of every two lobes in the 



(ZOOL. CI1ALL. EXP. PAET XII. 18S1.) M 5 



