EEPORT ON THE SIPHONOPHOR.E. 49 



Umbrella (PI. L. fig. 1, from below). — The umbrella is slightly vaulted, lenticular, 

 nearly discoidal, 4 to 6 mm. in diameter ; its vertical axis is about 1 mm. The margin 

 is regularly octolobate, with eight deep marginal incisions, from which arise the eight 

 bunches of tentacles. 



Exumbrella (PI. XLIX. fig. 7). — The superior face of the umbrella is rather flat, a 

 little vaulted, and exhibits a regular network of brown pigmented canals, the exumbrellar 

 vessels. Eight regular radial canals arise from a central circular canal, in the centre of 

 which is placed the apical stigma of the pneumatocyst. The eight interradial chambers 

 of the latter are separated by these perradial mantle canals, which anastomose outside 

 and form a ring around each chamber. From this ring arise in each octant four to 

 six centrifugal canals, which are forked and prolonged outside the pneumatosaccus 

 into the exumbrellar canals of the limbus. Their dichotomous branches are connected 

 by anastomoses. A few peripheral stigmata are scattered in the outer half of the 

 exumbrella. 



Limbus Umbrellas (fig. 7, um). — The free margin of the umbrella, outside the corona of 

 tentacles, is distinctly octolobate, and bears a series of pyriform marginal glands on its free 

 edge. The eight interradial convex lobes are more or less prominent between the eight 

 perradial bunches of tentacles. 



Subumbrella (PI. XLIX. fig. 11). — The inferior face of the discoidal umbrella is more 

 convex than the superior, and is divided into four different zones. The central zone is 

 occupied by the large central siphon (set). This is surrounded by a corona of sixteen 

 gonostyles, and this by an octagonal tentacular zone (fig. 12, tu). Outside the latter 

 is prominent the broad octolobate limb of the subumbrella. 



Pneumatocyst (fig. 8, half of the inferior face; fig. 9, half of the superior face). — The 

 subspherical central chamber (ph) possesses an apical stigma in the centre of its upper 

 face, and is surrounded by a corona of eight equal triangular radial chambers, each of 

 which bears a circular stigma. This octoradial central disc is surrounded by a peripheral 

 girdle composed of eight or nine concentric ring-chambers ; the second and third of these 

 (pk) are the broadest, much broader than the peripheral chambers. Eight deep perradial 

 furrows of the lower face separate the eight chambers of the octoradial ring one from 

 another, and are prolonged up to the circular margin of the pneumatocyst, dividing it 

 into eight slightly prominent lobes. In the middle between each two furrows (therefore 

 in eight interradial rows) may be seen the pneumathyras, or openings by which the 

 concentric ring-chambers communicate one with another (fig. 8, pg). 



The superior or apical face of the discoidal pneumatocyst (fig. 9) is slightly convex, 

 and bears about twenty stigmata, viz., one central, eight interradial (in the middle of the 

 eight triangular chambers), and eight to twelve peripheral, irregularly placed in the second 

 to the fourth ring-chamber. 



The inferior or basal face of the pneumatocyst (fig. 8) is slightly concave, and bears 



(ZOOL. CHALL. EXP. — PART LXXVII. — 1888.) Hhhk 7 



