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



they took with them an urticating streak of the urticating ring of the margin, and this 

 urticating streak becomes the umbrella clasp or " mantel clasp " ("peronium") (figs. 3, 

 4, en). This contains the basis of the tentacles in continuous connection with the 

 urticating ring of the umbrella margin, and so gives rise to a radial furrow, more or less 

 deep, of the umbrella collar which cuts through its gelatinous substance, but leaves the 

 subumbrella intact. Transverse sections show that the peronia are tolerably thick, solid, 

 clasp-like cords, consisting of a peculiar modification of urticating tissue ; numerous strata of 

 large spheroidal nematocysts lie closely accumulated one above the other. The distal end 

 of the umbrella clasp is in continuous connection with the urticating ring of the umbrella 

 margin (fig. 4, nc), whilst its proximal end is inserted at the spot where the tentacle 

 (t) runs out from its conical root (tr). The exumbral surface of each peronium lies 

 freely in the depth of the peronial furrow (between each two collar lobes), whilst its sub- 

 umbral surface is covered by the longitudinal muscle (fig. 5, mp) which rises from the 

 margin of the umbrella to the liases of the tentacle. Both lateral margins of the 

 peronium touch the adjacent peronial canals (ck). 



The four collar lobes (" lobi collares," fig. 4), which are separated by the four peronia, 

 are of a broad uniform shape ; their broad proximal basis falls in the coronal furrow of 

 the exumbrella, whilst their distal point forms the usually projecting part of the umbrella 

 margin (figs. 2, 3). Its distal external margin, which bears three auditory clubs on each 

 lobe, is joined to the velum; the lateral margins are limited by the peronia. The lobe 

 pouches (with the sexual products) lie in the concave internal or axial surface of the 

 collar lobes, whilst the external or abaxial half is vaulted convexly. The thin gelatinous 

 plate of the lobes is considerably thickened in the middle, and a sharp edge of the 

 exumbrella projects like a rib in the interradial middle line (figs. 1, 4, er). 



As in all Narcomedusae, the peculiar umbrella margin in Cunarcha ceginoides is 

 strongly indented in consequence of the dorsal change of position of the tentacles, and 

 supported by a strong urticating ring (fig. 4, nc ; fig. 7, nc). This consists, like the 

 peronia, of thickly accumulated nematocysts, and is covered with a ciliated sensitive 

 epithelium. The proximal margin of the urticating ring touches the annular canal (cc), 

 its distal margin rarely touches the velum (v). The two thin nerve rings (fig. 7, re' dorsal 

 or exumbral, re" ventral or subumbral nerve ring) which are separated from one another 

 by the supporting lamellae of the velum, lie on the two edges of the urticating ring. 

 The radial section (fig. 7) shows the more special anatomical and histological conditions 

 of the umbrella margin. (Comp. the explanation.) The umbrella margin of Cunarcha 

 (Bginoides has sixteen tentacular organs, namely, four long strong perradial tentacles, 

 four interradial large auditory clubs, and eight adradial smaller auditory clubs. 



The four perradial tentacles, which are common to Cunarcha and the nearly related 

 Canantha, remain permanent only in these two genera, whilst in all remaining Cunan- 

 thidae this original number either increases or only amounts to four in the first early 



