190 
THE VOYAGE OF H.M.S. CHALLENGER. 
sliaped dilatation before turning anteriorly to become tbe rectum. The intestine is 
thin walled, and it forms an open loop. Tbe spindle-sbaped dilatation and tbe rectum 
are separated by a constriction (PI. XXVI. fig. 4, Tbe rectum is wide and forms tbe 
dorsal edge of tbe abdomen and a considerable portion of tbe tborax (PI. XXVI. fig. 4, r.). 
Tbe anal aperture is small, with a reflected margin. 
Tbe mantle over tbe abdomen is considerably pigmented, especially in its posterior 
part, around tbe intestinal loop. Tbe pigment granules are opaque white. Tbe post- 
abdomen is very variable in length. It is of a dull yellow colour and is quite opaque, 
except along the middle line, where a narrow undulating clear streak represents tbe 
lumen of tbe septum. 
Polyclinum fungosum, n. sp. (PL XIV. figs. 15-23). 
Tlie Colony has a plano-convex discoid form. It is nearly circular in outline. Tbe 
lower surface is almost flat, and tbe point of attachment is at its centre ; there is no 
peduncle. Tbe upper surface is irregularly convex. Tbe colour is a dark duU grey. 
Tbe surface is uneven, and is roughened all over by a layer of small sand-grains 
adhering to tbe surface. No common cloacal apertures are visible. 
Tbe length (from tbe place of attachment to tbe highest point) is 1*6 cm., tbe breadth 
3 '3 cm., and tbe greatest thickness 2 '8 cm. 
The Ascidiozooids are very long, and are placed at right angles to the upper surface. 
Tbe largest measure about 8 mm. in antero -posterior extent and about 2 mm. in greatest 
breadth. Tbe anterior end is not wide. It forms a small projection on tbe surface of 
tbe colony about 1 mm. in diameter.' 
The Test is soft but fairly firm. Tbe outer layer is strengthened by imbedded and 
attached sand-grains and shell fragments. It is quite opaque and of a dull grey colour. 
In sections of tbe deeper layer of test tbe homogeneous matrix is seen to contain many 
small rounded cells ; tbe usual fusiform and stellate shapes are absent or rare. No bladder 
cells are present. 
The Mantle is rather thin. The transverse muscle bands are fairly strong, but are 
placed far apart. Tbe branchial sphincter is well developed. 
The Branchial Sac is very long and narrow. The transverse vessels are all similar, 
and are of moderate size. They have horizontal membranes attached to their inner 
edges. Tbe stigmata are long and narrow, usually with rounded ends. They are very 
regularly placed. 
The Dorsal Lamina is formed of a series of long pointed languets. 
The Tentacles are very numerous and closely placed. There are about twenty very 
long and thin tentacles and some intermediate smaller ones. 
