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



teeth are larger than the two median, and smaller than the two descending ventral teeth 

 (fig. 4, nx, right; nl, left). 



Exactly opposite to the basal face of the nectophores is the large axial or ventral 

 groove directed obliquely upwards and inwards ; it is limited by two prominent wings, 

 the axial edges of the two paired lateral faces ; these wings diverge towards the inferior 

 (ventral) and more strongly towards the superior (dorsal) end of the axial groove, while 

 they approach one another in the middle and at the dorsal corner of the groove (fig. 3). 

 A small and thin triangular lamella, the pedicle of the nectophore, arises in its sagittal 

 plane, in the middle of the axial groove, and is attached to the trunk of the nectosome 

 by its axial apex. Strictly speaking, that part of the axial groove which lies below the 

 pedicle is the ventral, and the opposite part, above the pedicle, the dorsal portion. 



The dorsal or abaxial face of the nectophore (superior half of fig. 4) is a convex, 

 vertical, nearly quadrangular plate, limited by four edges, and divided by three nearly 

 parallel ridges into four oblong facettes. Each of these ends below in a triangular 

 descending tooth ; the two median teeth being smaller than the two lateral. The 

 opposite superior edge of the dorsal face exhibits an odd median prominence and two 

 smaller paired lateral (fig. 4, above). 



The two paired lateral faces of the nectophore (right and left) are oblongish, convex, 

 smooth (figs. 1, 2), and prolonged below into the two ventral teeth, which embrace the 

 common stem of the nectosome. They are separated from the concave axial groove by 

 the prominent edge of the lateral wing, from the convex dorsal face by the vertical 

 lateral edge of the latter. 



Nectosac (figs. 2-5, iv). — The subumbrellar cavity, which occupies the bevelled basal 

 face of the nectophore, is very shallow (fig. 2, w, in profile). Its wide ostium is sub- 

 circular, slightly reniform owing to a small median notch on its ventral side. The 

 muscle-plate of the subumbrella is very thin and weak. The small velum (v) is sickle- 

 shaped, rudimentary in the ventral half, broader in the dorsal half. 



Canals of the Nectophores (figs. 2-4, c). — The nectocalycine duct passes from the 

 trunk through the small pedicle of the nectophore directly towards the top of the 

 subumbrella. Before reaching this, it gives off an odd long pallia! vessel, which ascends 

 obliquely in the jelly of the umbrella (immediately below the sagittal median line of the 

 axial groove) and ends blindly near the dorsal aj>ex of the nectophore (figs. 2-4, ce). 

 The four radial canals, which arise from the top of the subumbrella and are united by 

 the circular marginal vessel, are of very unequal length. The two paired lateral canals 

 (right and left) are little longer than the short dorsal canal and ascend- obliquely upwards, 

 close to the latter. Much longer is the ventral canal (cv), which descends obliquely and 

 before reaching the marginal canal expands in the form of a hexagonal or square ventral 

 sinus (cv"). Its form is very characteristic of the species ; it has six prominent corners, 

 two median in the sagittal axis, two smaller ventral and two larger dorsal on both 



