Polychaeta 17 B 



Scolecolepides arctius, n. sp. 



Type specimen. Cat. No. 36, Victoria Memorial Museum, Ottawa. 

 Paratypes, Victoria Memorial Museum, No, 37; Mus. Comp. Zool., No.'s 

 2194 and 2195. Four specimens. 



The type is about 23 mm. long, with a width of 1-7 mm. It consists of 

 about seventy-five setigerous segments. The body is flattened dorso-ventrally 

 and is pointed at both ends. 



The prostomium is long, pointed behind and broad, and truncate in front. 

 Posteriorly it reaches to the second setigerous somite. Four indistinct eye- 

 spots are present in the same position as in benhami but with those of the anterior 

 pair nearer to each other than the posteriors instead of the reverse. The appen- 

 dages are attached at the anterolateral angles somewhat beneath, as in benhami; 

 they are cylindrical and are proportionately much shorter than in the latter 

 species. No tentacular cirri are present. (PL III, fig. 5). 



The parapodia are of the usual biramous type. Each notopodium and 

 neuropodium has a prominent, flattened, postsetal lobe of which the notopodial 

 is longer than the neuropodial. The postsetal lobe in the anterior region is 

 vertically subelliptic with one edge attached (PI. Ill, fig. 6); but in the posterior 

 region it becomes proportionately narrower vertically and at the same time 

 higher (PI. Ill, fig. 7). The postsetal lobes decrease notably in size in the 

 caudal region. 



Branchiae are present on somites beginning with the first setigerous. They 

 are free from the notodial lobes excepting at their bases. Cylindrical and 

 filiform. They are moclerately long in the anterior region though in no case 

 equalling the width of the somite and behind the narrow pointed region scarcely 

 surpassing the middorsal line. The branchiae remain of nearly uniform length 

 and thickness until about somite XX when they begin to decrease in length 

 and thickness and practically cease on somite XXIX, though represented in 

 the form of nodules as rudiments at the bases of the postsetal processes. Pos- 

 terior region wholly free from branchiae. 



The setae in both notopodia and neuropodia are in two series, an anterior 

 and a posterior one, in addition to those of the inferior ventral group and superior 

 dorsal group. In both branches of all paradodia occur fine capillary, apparently 

 non-limbate setae in an anterior series, and broader, limbate setae in a posterior 

 series. In going caudad a limited number, mostly three or four, hooded crochets 

 replace setae of the posterior seties, first in the neuropodia and then in the noto- 

 podia, the setae of the anterior series remaining unchanged. The setae of the 

 inferior ventral group are bilimbate, distally pointed, the tips curving caudad 

 and usual. The superior dorsal setae are much more elongate than the more 

 ventral ones. In a typical neuropodium of the middle and posterior regions, 

 at least, there is also a corresponding dorsal neuropodial group of more elongate 

 capillary setae, though these were not detected in all cases. (See PI. Ill, fig. 7). 

 The crochets are of the usual general form, distally narrowed and bidentate, 

 and hooded. The hooded region colorless, more or less transparent; the bafi 

 in part strongly fibrillate. (See PL IV, fig. 1). 



Anus surrounded with numerous short papillae. 



LOCALITY. Alaska: Collinson point. Station 27o. September 20, 1913. 

 Mr. Johansen's field-note accompanying these specimens states that they were 

 " Pelagic under 5 inches of ice over 1 foot of water in lagoon at Collinson poiDw 



Alaska: Lagoon at Collinson point. Station 27i. September 18, 1913. 

 " Pelagic under 5 inches of ice over 4 feet of water." Two anterior fragments. 



This species, so far as appears from Ehlers' account of S. benhami 1 , is 

 congeneric with the latter, the only other known Scolecolepides. The type ot 

 S. benhami was taken by Prof. Benham at Moeraki, South New Zealand. Tbe 



!Abh. K. Ges. Wiss. Gottingen, Math.-phys Kl., n.s. 1907 5, no. 4 D. 14. 



719272 



