238 DISCOVERY REPORTS 



Illustrations of sagittal and transverse sections passing through the gill region are 

 given in Plate XXXVI, figs. 3-6. The external gill slit (eg) opens into a cavity (gc), placed 

 between the body wall and the wall of the pharynx. The wall of this gill cavity is formed 

 of vacuolated tissue, called pleurochord. In other species there is a deep groove running 

 along the entire length of the pleurochords on either side of the pharynx, which starts 

 from the gill slit, and probably the respiratory water traverses these grooves. The gill 

 cavity found in this species may have originated by the enlargement of the groove and 

 the fusion of the lips, resulting in the formation of a tubular space (gc) between the 

 pharynx and the body wall, opening on the one side into the external gill slit, and on 

 the other into the pharynx by a narrow slit, which for convenience will be termed the 

 internal gill opening (7^). Whereas in other species water passes directly from the 

 pharynx through the gill slit, the intervention of this cavity makes the passage of the 

 respiratory water more complicated. Water flows from the pharynx through the internal 

 gill opening into the gill cavity whence it passes out through the external gill slit. 



The proboscis, which is oval with indented sides, is small compared to the zooid. It 

 is i-i mm. long and 0-9 mm. broad. The red line runs near the posterior margin. 



There are always eight pairs of arms without end swellings. The pinnules on the basal 

 parts are 0-4 to 0-5 mm. long. The dorsal wall of the arm has a thick layer of vacuolated 

 cells each of which encloses a refractive bead similar to those in the end-swellings of 

 C. dodecalopJms and C. hodgsotii. This layer curves over the tip of the arm so that a few 

 refractive beads occur in the tip also. Thus although end-swellings are not found, there 

 are refractive beads in the tips. The arms on the extreme right and left sides are directed 

 downwards on either side of the mouth in the preserved condition. The longest arms 

 measure 17 mm., but those towards the sides are shorter. 



The stolon varies considerably in length and thickness. In some it is thin and about 

 25 mm. long, and in others thick and short, with a brownish tint on one side. The 

 difference in length of the stolon is probably due to contraction when the zooids were 

 fixed, but even in the contracted state it is much longer than the stolon of other species^. 



Cephalodiscus fumosus, n.sp. (PI. XXXIV, fig. i). 



Diagnosis. Colony unbranched, in the form of a brittle arenaceous cake, measuring 

 90 mm. across and 16 mm. high and consisting of evenly distributed (5 to 7 mm. apart) 

 vertically disposed tubes of uniform diameter. Tubes pale brown, buried in the common 

 mass, which is formed of a dense agglutination of minute sand grains. Each ostium 

 produced on one side into a short thick triangular lip, which can fold over like an oper- 

 culum. Those in the middle of the colony 14 mm. long, those near the edge shorter. 

 Width of the tube near the ostium 1-4 mm. Length of fairly extended zooid from tip 

 of arms to base of body 3-2 mm., length of arms 1-2 mm., width of body i mm. Colour 



1 Sir Sidney Harmer, when reading through this paper, suggested that during life the length of the stolon 

 varies greatly from time to time, but that this point was not sufficiently appreciated by earlier workers who 

 very often cited the length of the stolon of the preserved zooid as a diagnostic character of the species of 

 Cephalodiscus. 



