VOhYCli.KTA FROM NORTU 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. LXXXIX. 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 h). 



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



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



4. Some setae of 3rd fascicle bladed sickles (fig. 11 c). 



A few large specimens from San Juan Island on bai-nacle- 

 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 pinna? ; oj)erculum not unlike 

 that of ^S'. ambilateralis, 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. \\d); the uncini have the usual shape. 



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

 or four brush-like setse and a long asetigerous anal segment. The 

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

 this and the last described species of Spirorbis : 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 very thin wall, the 

 large ova causing marked protuberances on its surface, the whole 

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



Sub-genus LiEospiRA. 



1. Tube sinistral. 



2, Thorax with 3 setigerous segments. 



