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



apertures are placed. The branchial aperture is at the ventral edge of the anterior end; 

 it is prominent, and is turned ventrally and a little to the left. The atrial aperture is at 

 the dorsal edge of the anterior end ; it is not quite so prominent as the branchial, and is 

 turned dorsally and a little to the left. 



The surface is very uneven, and is deeply wrinkled and rather rough. The colour is 

 yellow and dark brown. 



Length of the body, 4 "5 cm. ; breadth of the body, 3 cm. 



The Test is thin, except at the posterior end, where it is thickened ; it is tough and 

 opaque, and is white on section and on the inner surface. 



The Mantle is rather strong and muscular. 



Tlie Branchial Sac has the folds very slight and distant ; there are seven on each side. 

 The transverse vessels are mostly wide but irregular. The internal longitudinal bars are 

 numerous ; there are about nine on a fold and eight in the interspace, which has four 

 wide and four narrow rows of meshes. The meshes contain each about four short oval 

 stigmata, and are often divided by narrow horizontal membranes. 



The Dorsal Lamina is formed of a series of narrow tentacular languets. 



Tlie Tentacles are compound, they are very small, and consist of twelve larger ones, 

 with either one or two very minute ones between each pair of larger. 



The Dorsal Tubercle is very large, but irregular ; it is broken up into a number of 

 curved pieces. 



This species is very irregular in external appearance (PL XVI. fig. 10), and has a good 

 deal the look of a Microcosmus, with its creased and furrowed, thin but tough and stiff 

 test, of a yellow and brownish colour. 



The branchial sac (PL XVI. fig. 11), is also rather irregular. There are fourteen folds, 

 but they are not very wide although each has a considerable number of internal longi- 

 tudinal bars upon its surface. The space between each pair of folds has usually eight rows 

 of meshes, four of which are wide and four narrow (PL XVI. fig. 11). 



The dorsal tubercle is the most remarkable feature in this species (PL XVI. fig. 12). 

 It occupies the greater part of a triangular and rather deep peritubercular area, and is 

 present in the form of eight or nine distinct apertures of irregular shajjes, and each 

 bounded by a raised lip. These apertures are arranged in the form of a deeply cup-shaped 

 curve, and look as if they were the remains of a tubercle of the ordinary type, with the 

 aperture anterior and both ends bent slightly to the left, which had had its originally 

 single curved slit broken up into the series of separate apertures. 



One specimen of this species was found at Port Jackson, Australia ; depth, 2 to 1 

 fathoms. 



