10 B Canadian Arctic Expedition, 1913-18 
Nepthys hudsonica, n. sp. 
Type specimen.—Cat. No. 51, Victoria Memorial Museum, Ottawa. 
Paratype, Mus. Comp. Zool. Two specimens. 
The general colour of the type is light brown of a weakly pinkish tinge. 
There is a distinct median longitudinal dark line along the dorsum, the ventral 
neural line being also somewhat darker. The paratype is darker, particularly 
so in spots proximad of some’ parapodia above and on part of the presetal lobes. 
The type is composed of eighty-six somites. It has a total length of 69 mm., 
exclusive of the proboscis which is only partially protruded. The maximum 
width is 5 mm., this being at the anterior end near the eighth somite, this end 
of the body being relatively broader, much less narrowed cephalad, than, e.g., 
in N. caeca. From this widest region the body narrows at first more rapidly 
and then very gradually to the caudal end. 
The prostomium is somewhat trapeziform with middle of the narrower 
caudal end somewhat angularly produced, the form thus somewhat subpenta- 
gonal; anterior margin broad, gently convex. Anterior region not protruding 
forwards as it does in caeca and ciliata. Posterior tentacles attached on each 
side at ectal end of anterior margin but little farther caudad than the corres- 
ponding anterior tentacle. Tentacles proportionately short and thick, much 
less slender than in ciliata, the posterior or outer ones stouter and a little longer 
than the inner ones (PI. II, fig. 4.) On each side at caudolateral angle is a 
prominent sensory papilla. The mouth appears not to be bordered by such 
fleshy lateral lips with papille as are so prominent in caeca, etc. The broadly 
triangular membrane appearing at the caudal edge of the mouth like a lower 
lip shows transverse sulci or folds in place of the usual longitudinal ones. 
The first setigerous somite is incomplete, being evident only on each side 
of the prostomium, from which it extends to the border of the mouth on each 
side, being thus incomplete both dorsally and ventrally. It bears only the 
notopodia as usual. The second somite, bearing also only notopodia, is complete 
above though the caudal angle of the prostomium extends into it and nearly 
ae it. In the succeeding somites the parapodia are biramous. (See PI. IT, 
g. 4. 
The notopodia of the second somite are farther dorsad than those of the 
first and than those of the third, those of the succeeding somites descending 
to the sixth or seventh after which they remain at the same level. The first 
two pairs of notopodia have the same general structure as the succeeding ones, 
though slender and with the branchial appendages shorter and more conical, 
these being the so-called tentacular cirri of Ehlers. In a typical parapodium 
the postsetal lamella of the notopodium is a low convex lobe highest subvertically 
and decreasing and disappearing distad in strong contrast with the prominent 
lobe of caeca and lower than usual in ciliata, ordinarily not exceeding the summit 
of the lobe. The branchial appendage is long and ordinarily curved in a semi- 
circle with its concavity ectodorsad. The cirrus, arising from the base of the 
branchial appendage, is slender and subulate. The neuropodium is broad, 
widening distad and with the distal end long, gently convex and mesally incised 
like that of the notopodium. Postsetal lamella low, short, scarcely exceeding 
the apex of the lobe. (See PI. II, fig. 5, 6.) 
The acicula are dark. The tip of each extends into a projecting conical 
papilla as usual. The sete have the usual general arrangement. The coarse 
posterior sete are dark, while the finé, camerated anterior sete are pale. (See 
Pl. II, fig. 5). 
The anus is terminal. From its thickened ventral edge arises a median 
ae ee cirrus of moderate length which reaches only to the penult setigerous 
segment. 
The proboscis as extended in the paratype is 3-6 mm. long and widens 
from base to bevond middle where it is 3-4 mm. wide. Bearing twenty-two 
