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



pyramidal caudal apophysis. Whilst the superior half of the dorsal face is nearly 

 vertical, square, aud concave, its inferior peutagoual half is convex aud prominent, directed 

 more dorsally downwards, and bisected by a sagittal crest which becomes obsolete towards 

 the upper half. This crest bears about the middle of its length an odd prominent tooth 

 (figs. 13, 14). 



The two-paired lateral faces of the bract (right, fig. 13 ; left, fig. 14) are hexagonal, 

 square and vertical in their upper half, irregularly hexagonal and more prominent in the 

 lower half. The superior horizontal edge of each lateral face is half as long as the 

 ventral, and one-third as long as the basal and the dorsal edge. The vertical ventral 

 edge is concave. The opposite dorsal edge bears a prominent tooth between its middle 

 and lower thirds, and so also does the obliquely descending basal edge. 



The basal or inferior face of the bract is occupied by the square opening of the 

 bracteal cavity (fig. 15, middle portion), and behind this by the triangular ventral face 

 of the caudal apophysis (fig. 18). 



The caudal apophysis, which distinguishes the cuboidal bract of Aglaisma from the 

 similar bract of Cuboides (PI. XLIL), is a bilateral oblique pyramid, which descends from 

 the prolonged dorsal and basal part of the hydrophy Ilium. The pyramid is five-sided, 

 directed downwards and dorsalwards up to the apex, which is slightly curved inwards. 

 The five angles of its base are marked by the five above-mentioned teeth, viz., the odd 

 dorsal tooth of the sagittal crest (in the inferior half of the dorsal face), the paired teeth 

 of the latero-dorsal edges, and the paired (somewhat inferior) teeth of the lateral basal 

 edges. 



All the edges of the polyhedral transparent bract are elegantly denticulate, and 

 more or less curved. 



The bracteal cavity (figs. 13-18, ui) opens in Aglaisma (as in Cuboides) more on the 

 basal or inferior face ; whereas in Amphiroa and Sphenoides the aperture is rather on 

 the ventral or anterior face. It occupies the greater part of the inferior half of the bract, 

 and is obliquely campanulate. The apex of the cavity is directed dorsally. 



Phyllocyst (figs. 13-18, be). — The phyllocyst is a small subspherical cavity, placed 

 immediately above the basigaster (sb), and gives off four large canals, two odd and two 

 paired, which are comparable to the four radial canals of a bilateral Medusa. The 

 superior odd canal (cv), which corresponds to the original ventral canal of the Medusa, 

 ascends vertically near the median line of the dorsal face, and ends above in a spindle- 

 shaped diverticulum which includes an oleocyst (co). The inferior odd canal (cd) 

 is somewhat longer, also placed in the median plane, and descends obliquely downwards ; 

 it runs parallel to the neighbouring dorsal crest, and corresponds to the dorsal radial 

 canal of a Medusa. The two paired lateral canals (ex right, el left) are much shorter, 

 wider, and sac-shaped, as in Cuboides. They are geniculate and filled by large vacuolate 

 entoderm-cells ; their dorsal half is placed nearly horizontally, whilst their ventral half is 



