382 
THE VOYAGE OF H.M.S. CHALLEHGEE. 
appendage, and a crenate shorter one. The smooth branchial processes (second and third) 
are absent. 
The feet differ in shape from those of the species mentioned. Thus at the fourth the 
outline of the superior lamella is more convex externally, and the inferior lamella is smaller. 
The bristles are also considerably shorter and stouter, both dorsally and ventrally, in the 
new form. The differences become more pronounced at the tenth foot, in which the long 
ventral bristles are much more delicate than those of the dorsal division, and the 
lamella of the setigerous region is less prominent. ' In the Challenger form, moreover, 
the tenth foot has hooks, whereas none occur in that of Prionospio steemtrupi. The 
shorter and stiffer dorsal bristles are also characteristic. 
In regard to the minute structure of the hooks of the new species it is found that 
there are several denticulations above the great fang (PI. XXIVa. figs. 7, 8), the 
smaller hooks, perhaps, showing these structures somewhat better than the larger, as they 
are more readily seen in profile. 
The structure of the body-wall is nearly the same as in Prionospio steenstrupi, 
though the longitudinal dorsal muscles form a thinner la}mr on each side. The 
hypoderm is thicker laterally and ventrally. In both the neural canals are large. The 
pharyngeal wall has externally a circular layer, then the basement tissue upon which the 
folded glandular coat rests. In this region (anterior third) it also presents a muscular 
sheath of external circular and internal longitudinal fibres, while various strong muscular 
fasciculi, apparently connected with protrusion and retraction, are attached to the sheath 
superficially. A large blood-vessel occurs over the insertions of the oblique muscles 
interiorly, and another between the longitudinal dorsal muscles superiorly. Numerous 
minute ova existed in the perivisceral chamber. 
In his remarks on Prionospio steenstrupi from Madeira, Langerhans ^ describes and 
figures the great “ Leydigschen Fasern ” of the ventral nerve-cord. As this species 
possesses two large neural canals towards the upper surface of the nerve-cord, some 
discrepancy appears to be present, for Langerhans shows only a single median dark band 
under the action of osmic acid. 
Family Cirratulid.®:. 
The two divisions of the- Cirratulidae represented in the collection are separated by a 
wide interval in regard to habitat. Thus the genus Cirratulus is almost entirely a 
littoral form, abounding under stones in mudely and even odoriferous localities ; while 
ChcBtozone frequents the deeper water, descending in the present case to 1250 fathoms, 
and apparently being partial to the blue mud, in which it probably burrows. This genus, 
* Zeiischr. f. wiss. ZooL, Bd. xxxiv. p. 91, Ta^. iv. fig. 3 1880. 
