394 SPIRORBIS SPIRILLUM. 
1915. Spirorbis spirorbis, Southern. Irish Sc. Invest., No. 3, p. 49. 
$s >) spirillum, Allen. Journ. M. B. A., vol. x, p. 645. 
1916. 7 i McIntosh. Ann. Nat. Hist., 8th ser., p. 189. 
1917. & 5 Borg. Zool. Bidr. Uppsala, Bd. v, p. 20, text-figs. 3 and 4. 
1919. Circeis < Chamberlin. Mem. Mus. Comp. Zool., vol. xlviu, p. 478. 
1920. - » . idem. Canad. Arctic Exped., vol. ix, Part B, p. 28. 
»  Sptrorbis - Eliason. Faun. Oresund., p. 80. 
Habitat—Abundant on zoophytes all round the British shores; on Fuci, Algze and 
Corallina officinalis (Fleming); on Flustra, etc. The variety (Sp. semistrorsa) is found on 
crabs and lobsters (Montagu). Firth of Forth (Leslie and Herdman). Loch Fyne; Loch 
Alsh (J. G. J.); Dublin Bay, Dalkey Sound, and West Coast of Ireland (Southern) ; 
Plymouth, on Sertularia abietina, etc. (Crawshay), and south bank of the River Yealm, 
Plymouth ; Torquay (Elwes). 
Abroad it has been noted as follows :— 
N. Pacific Coast and N.E. Coast of N. America (Moore); Greenland (Michaelsen and 
Ditlevsen) ; Coast of Korea (Levinsen) ; Vancouver Island (Pixell) ; Spitzbergen and North 
Sea; common in Finmark (Norman); Franz-Joseph-Land (Augener) ; Cape Fox, Alaska, 
and to Santa Barbara, California, and on the eastern shores of North America (Bush) ; 
Canadian North-West Territories (Chamberlin) ; Smith’s Sound (Brit. Museum); Barents 
Sea (McIntosh); Kara-Havet (Levinsen); Mediterranean (if Spirorbis Pagenstechert is same) ; 
New England and Atlantic Coast, U.S.A. (Verrill). 
The collar agrees with that in other Spirorbids in being widely split dorsally, but 
continuous ventrally. Its connection with the membrane of the anterior setigerous region 
is also normal. The branchiew are four on each side, and the terminal processes of the 
filaments are short, so that they do not project beyond the pinne, which thus form 
a more or less even tip (Plate CX XII. fig. 90). 
The operculum forms a shallow vase with a foot or process beneath, the edge of the 
latter being crenate (Plate CXXII, figs. 9 and 9a, and Plate CXXXII, fig. 6e). There 
is no space for opercular embryonic development in this species. 
The body is widest in front, and gradually tapers to the tail. 
The collar-bristles (Plate CX XXII, fig. 6) are characterised by the absence of the gap 
near the base of the terminal blade. They are comparatively small, have long straight 
shafts, which dilate on reaching the distal shoulder, the terminal region being sharply bent 
backward, tapered to a fine point, and rather coarsely serrated along the edge, especially 
at the base. The figure of the collar-bristle as given by Miss Pixell' from the Pacific Coast 
of North America diverges considerably from the British form, the tip beimg shorter and 
broader. The other bristles conform to the usual type. The second fascicle consists of 
simple winged bristles (Plate CX XXII, figs. 6a and 6a’), and the third appears to have similar 
bristles. The posterior bristles have the tips bent at an angle (geniculate) (Plate CX XXII, 
fig. 6b), and usually project little in the preparations. — 
The hooks (Plate CX XXII, fig. 6f) are somewhat triangular in shape, with a series of 
sharp teeth along the anterior edge, which terminates inferiorly in a larger process at a slightly 
1 “Proc. Zool. Soc.,’ 1912, pl. Ixxxviii, fig. 8c. 
