POLYCHiETA FROM NORTH AMERICA. 799 



developed, for according to Caullery & Mesnil (5) the possession 

 of blade and fin is not a primitive characteristic, and they are 

 also very large ; possibly they are specially developed in correla- 

 tion with its habitat in rapids where the tide runs from 7-9 knots 

 an hour. The presence of the specially developed brood-pouch 

 might perhaps receive a similar explanation. 



Sub-genus Paral^ospira, 



1. Tubes sinistral. 



2. Thorax with 3| setigerous segments. 



11. Spirorbis racemosus, sp. n. (PI. LXX.XIX. fig. 11.) 



Specific characteristics : — 



1. Collar setae with fin-like expansion at base of very coarsely 



serrated blade (fig. 11 a). 



2. Operculum with massive talon having lateral wings and a 



hook on ventral surface (fig. 11 b). 



3. Thin-walled dorsal or lateral brood-pouch attached to the 



thorax at the base of the operculum (fig, 11 d). 



4. Some setse of 3rd fascicle bladed sickles (fig. 1 1 c). 



A few large specimens from San Juan Island on barnacle- 

 shells overgrown with calcareous sponge ; smaller ones from 

 Channel outside Departure Bay. Depth in both places 15 to 

 25 fathoms. 



The largest specimen measures 5 mm. across the spiral ; the 

 tube is corrugated and generally rather loosely coiled, leaving a 

 central hole. 



Branchiae 13 — 6 functional ones on each side; rachises have 

 short tapered extremities without pinnae ; operculum not unlike 

 that of iS. amhilateralis, but the talon rather more massive and 

 its outer concavity almost hemispherical and filled with debris. 



The collar setae are very large (fig. 11a); the 2nd fascicle 

 consists of plain-bladed setae, and the 3rd contain some fringed 

 sickles as well. There is a distinct third uncinigerous torus on 

 the left side (fig. 11 c?) ; the uncini have the usual shape. 



There are 21 well-marked abdominal segments, each with three 

 or four brush-like setae and along asetigerous anal segment. The 

 brood-pouch with its distinct wide stalk seems to be peculiar to 

 this and the last desciibed species of Spirorhis : it does not appar- 

 ently replace a gill, for the calcareous operculum is developed as 

 usual on the 2nd to the left. The sac has a vexy thin wall, the 

 large ova causing marked protuberances on its surface, the whole 

 somewhat resembling a bunch of grapes (fig. 11 d). 



Sub-genus L^ospira. 

 1. Tube sinistral. 

 .2. Thorax with 3 setigerous segments. 



