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 (PL 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 papillae 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 

 bisects it. In the succeeding somites the parapodia are biramous. (See PL II, 

 fig. 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 PL II, fig. 5, 6.) 



The acicula are dark. The tip of each extends into a projecting conical 

 papilla as usual. The setae have the usual general arrangement. The coarse 

 posterior setae are dark, while the fine, camerated anterior setae are pale. (See 

 PL II, fig. 5). 



The anus is terminal. From its thickened ventral edge arises a median 

 tapering 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 



