104 THE VOYAGE OF H.M.S. CHALLENGER. 



exumbrella and touch both the umbrella disc and the umbrella corona, whilst the deeper 

 subradial furrows are confined to the umbrella corona. Of the sixteen shallow, longi- 

 tudinal furrows, four are perradial, four interradial, and eight adradial. They are placed 

 at equal distances in the central umbrella disc, and divide its peripheric, thickened half 

 into sixteen equal, subradial disc-swellings, whilst its thinner central half remains 

 without furrows, and is, at the same time, considerably thinned away (figs. 1, 13, 14). 

 In the peripheric umbrella corona, on the other hand, they are only distinctly impressed 

 in the distal part of the sixteen coronal swellings. The deeper sixteen subradial 

 longitudinal furrows, which traverse the entire corona of the umbrella, lie between the 

 sixteen coronal swellings, and are placed in pairs in such a way that the umbrella 

 corona is divided into eight narrower and eight broader gelatinous sockels or pedalia ; 

 the former bear the eight rhopalia, the latter the eight tentacles (figs. 1, 13). Each of 

 the sixteen gelatinous sockels consists of a thicker, undivided proximal part and a 

 thinner distal part, halved by a shallow, radial furrow ; the former contains a coronal 

 pouch, the latter a pair of lobe pouches. The eight narrower, principal ocular sockels 

 (" pedalia rhopalaria "), four perradial {up), and four interradial {wi), are distinguished by 

 their side lines being sinuated concavely, and their narrower proximal part being only half 

 as long as the bifurcate distal part. The eight broader adradial tentacular sockels 

 (" pedalia tentacularia," ww), on the contrary, show convexly projecting side lines, and 

 their broader proximal part is nearly twice as long as the deeply inserted distal part 

 (figs. 1, 13). The ends of the bifurcate halves are rounded obtusely in all sixteen 

 pedalia, and sharply defined from the marginal selvage of the marginal lobes 

 (" patagium," Ip). 



The subumbrella (figs. 12, 13) is divided into three sections by the broad coronal 

 muscle (one), by whose two margins they are separated from one another. Its inner or 

 upper intracoronal third reaches from the insertion of the stomach (relatively from the 

 four pyloric valves or interradial septal nodes) as far as the inner or proximal margin 

 of the coronal muscle (mc), and contains both the proximal halves of the eight adradial 

 genitalia (s), and the narrow longitudinal deltoid muscles alternating with them ; of 

 these muscles, as in Atolla (PL XXIX.), the four interradial (fig. 12, md) are much 

 stronger and broader than the four perradial (fig. 12, md). The middle or coronal third of 

 the subumbrella is occupied solely by the broad coronal muscle ("museums coronalis," figs. 

 12, 14, mc). This comports itself precisely as in Periphylla, and is divided by the 

 sixteen fused clasps of the marginal lobes (fig. 12, hi) into sixteen quadrangular coronal 

 area?. Of these the eight adradial (tentacular) are considerably broader than the eight 

 principal (rhopalar) ; the former cover, at the same time, the distal halves of the 

 genitalia on their axial side. The external or lower extracoronal third of the 

 subumbrella extends from the outer or distal margin of the coronal muscle (me 4 ) to 

 the actual margin of the umbrella, and is occupied by the corona of lobes. In it 



