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



Medusen, 1879, p. 389). The four strong tseniola contain a well-developed, longitudinal 

 muscle (figs. 13, m ; 14, m) ; this is enclosed in a voluminous gelatinous sheath (ft), which 

 is considerably thicker on the axial side than on the abaxial side, and which internally 

 forms numerous dendritically branched folds. The muscular plate of the peduncle (m) 

 is extended on these folds of the gelatinous supporting plate ; it encloses a central axial 

 cord of exoderm cells (q) lying in the axis of the tseniolum ; there are the " epithelial 

 muscular cells " of the exumbrella which have immigrated centripetally from its outer 

 surface into the gelatinous selvage. The delicate figure shown by each tamiolum in its 

 oval transverse section (fig. 14) consists, from its axis towards its periphery, of the 

 following layers : — (l) The central cell-cord of the ectodermal epithelial muscular cells 

 (q) ; (2) the folded muscular plate arising from it (m) ; (3) the fulcral lamella (z) with its 

 dendritic supporting folds, and the thick gelatinous sheath surrounding it (ft) ; (4) the 

 endodermal covering of the gastral epithelium (d). 



The cup ("calyx"), or the peculiar "umbrella" of our Lucernaria (after removing 

 the stalk) is almost oval, broadest in the middle, gradually passing into the conical 

 peduncle above, and slightly contracted below towards the umbrella margin and the 

 eight arms (figs. 1-3). As in all Stauromedusse, the umbrella consists of two thin walls, 

 an external convex umbrella and an inner concave suluimbrella. The two walls enclose 

 the hollow space of the gastrovascular system, pass into each other at the umbrella 

 margin, and are otherwise only connected with each other by the four interradial septa 

 (" lines of fusion, or cathammal selvages," h). The two walls consist in section chiefly 

 of a thin but firm gelatinous plate (fulcral lamella, z) ; its inner side is covered by gastral 

 endoderm (d), its outer side by dermal exoderm (q). The external convex surface of the 

 umbrella or the true exumbrella (e) is smooth, without special characteristics, and only 

 traversed by four slight interradial longitudinal furrows (the distal processes of the 

 peduncle furrow). The gelatinous substance under the exumbrella is not thick but very 

 firm, and traversed by numerous elastic fibres which run from the outer to the inner 

 surface of the gelatinous plate (fig. 13, uf) ; they are also equally numerous in the thin 

 gelatinous plate of the subumbrella (fig. 18, uf). The ectodermal epithelium of both 

 the exumbrella and the subumbrella is armed with scattered urticating organs (comp. 

 my System cler Medusen, 1879, p. 382). 



The antrum or umbrella cavity (" necto-calyx ") (h), which is lined by the ectoderm 

 of the subumbrella (qw), is divided in our species, as in all Lucernaridse, into two parts, 

 the lower (distal), simple, coronal umbrella cavity, and the upper (proximal), quadrilocular, 

 funnel umbrella cavity. The coronal umbrella cavity (fig. 5, he, " antrum coronarium ") 

 is perfectly simple, cylindrical, or almost cubic, and occupies the entire lower half of the 

 body ; the eight deltoid muscles, and the distal halves of the genitalia he in its sub- 

 umbrellar wall. The funnel umbrella cavity (" antrum infundibulare," i) is divided from 

 the coronal umbrella cavity by the oral boundary-line E F (figs. 2, 3), and is composed of 



