332 
THE VOYAGE OF H.M.S. CHALLENGEK. 
divisions, the inner being shorter than that between it and the cirrus. It thus quite 
differs from Nothria ehlersi, which has three branchial divisions in this foot. Moreover, 
both dorsal cirri and branchiae are more slender than in the species just mentioned. 
A single branchial process exists on the fortieth foot, and it is about the same length as 
the dorsal cirrus, whereas in Nothria ehlersi the branchia has three divisions on the 
same foot. A small branchial lobule occurs at the base of the dorsal cirrus of the 
fiftieth foot, but it disappears before the sixtieth foot is reached. In this species, 
therefore, the branchiae are somewhat more feebly developed than in its congener, to 
which, however, it is closely allied. 
There is no very evident distinction between the dorsal bristles of the two species. 
Both are elongate, with finely tapered tips and narrow wings. The brush-shaped bristles 
(PI. XXVIa. fig. 9) also closely resemble those of the preceding species. 
The long hooks (PI. XXVIa. fig. 10) agree with those of Nothria ehlersi in most 
details, though they are shorter and broader. There is less space between the tip and 
the commencement of the shaded region, and the distal prong is less acute. 
The tube formed by this species is of a light greyish colour, and almost entirely com- 
posed of Diatoms and Radiolarians. It is friable, and contrasts strongly with a large tube 
of a Sahella from the same Station, for the latter is remarkably tough, probably from the 
great development of the inner lining of chitinous secretion, though the external greyish 
coating is of the same microscopic structure. 
In section the cuticle is of considerable thickness, both dorsally and ventrally. 
Over the thick hypoderm of the lateral regions, however, it is thinner. With the 
exception of the lateral increase just noted the hypoderm is feebly developed. The 
eircular muscular coat- is also somewhat thin. Both dorsal and ventral longitudinal 
muscles are large, as also are the vertical muscles by the side of the alimentary canal. 
Some oblique muscles proceed from the outer borders of the dorsal longitudinal, and with 
the inferior oblique join the circular coat at the ventral surface. The arch from the 
alimentary canal encloses the nerve-area, which is bounded externally by the circular 
coat. The glandular region is close to the outer border of the dorsal longitudinal 
muscle, and thus in many sections it appears above the bases of the spines and bristles. 
The thickened hypoderm over this region is thus much higher than in Nothria ehlersi, 
the glandular tissue of which generally presents itself below the bristles. 
Nothria quadricuspis (M. Sars). 
Onuphis quadricuspis, M. Sars ; G. O. Sars, Bidrag Kundsk. Cliristianiafjordens Fauna, Bd. 
iii. p. 16, Tab. xv. figs. 7-19. 
Habitat. — Dredged by the “Knight Errant,” Station 6, August 11, 1880; lat. 
59° 37' N., long. 7° 19' W.; 530 fathoms; bottom temperature 46°‘5, surface tem- 
perature 57°‘0 ; sea-bottom, grey mud. 
