KEPOET ON THE DEEP-SEA MEDUS-E. 115 



furrow, which corresponds to the middle line of the disk teeth, and of the rhopalar 

 pedalia. Their axial surface forms the outer, almost perpendicular or only slightly 

 overhanging wall of the coronal furrow, whilst their abaxial surface serves for the insertion 

 of the proximal tentacle bulb. 



The gelatinous sockels of the sense clubs ("pedalia rhopalaria ") alternate regularly 

 with the gelatinous sockels of the tentacles, and form the second middle zone of the 

 umbrella corona (figs. 1, 4, no). They are nearly as large as the tentacular pedalia, 

 somewhat longer but not so thick, and are inserted with their proximal part between the 

 distal sides of the latter. Their upper aboral surface is almost pentagonal, and depressed 

 (fig. 1, uo). Their lateral margins are separated by a broad interspace which is filled 

 by the bulb of the tentacle. Its truncated distal margin bears a pair of thin marginal 

 lobes and the rudiment of a sense club in the incision between the pair. 



The marginal lobes (" lobi marginales," fig. 4, I) form the third or outer zone of 

 the umbrella corona. They amount in number from 38 to 44, as each marginal 

 lobe is inserted between a tentacle and a rhopalium. Their shape is a longish round, 

 2-3 mm. broad, 5-6 mm. long. The proximal third of each marginal lobe consists 

 of a thick semi -oval gelatinous part, which is merely the distal bifurcation of a rhopalar 

 pedalium. The middle and distal third of the marginal lobe is formed by a very 

 thin membranous, folded marginal border (" patagium," Ip). This was invariably torn 

 and badly preserved. 



The gelatinous disk (wo/) of Atolla is thick and firm (fig. 4, left half, in vertical 

 meridian sections). It has the consistency of a tolerably firm fibrous cartilage. In the 

 central umbrella disk (uc) its thickness amounts to 5 mm., even to 10 mm. at the 

 thickest part at the marginal teeth (er) ; whilst immediately outside these, at the thinnest 

 part of the coronal furrow (ec'), it is only h mm. The gelatinous substance of the pedalia 

 is from 4-7 mm. thick. 



The umbrella margin of Atolla includes all the parts lying outside the coronal muscle, 

 and is therefore composed of from nineteen to twenty-two tentacles, the same number of 

 sense clubs alternating with them and twice the number of marginal lobes, inserted 

 between the former and the latter. The rhopalia at the distal margin of the rhopalar 

 pedalia are, however, so small and the two marginal lobes at the distal end of the pedalia, 

 which enclose the rhopalia, are so closely united, that at a superficial glance it looks as if 

 the umbrella margin was merely composed of alternate tentacles and rhopalar pedalia. 

 Closer investigation and comparison with the more completely developed umbrella 

 margin of the closely allied Collapsis (System, pi. xxvii.) shows, that the umbrella 

 margin is essentially composed like that of the latter, only that the sense clubs and their 

 pouches have undergone much greater retrograde formation in Atolla. 



The tentacles (figs. 1-4, t) are very weak, hardly half as long as the radius of the 

 umbrella, they are shaped like an awl and finely pointed towards the thin end. 



