412 SPIRORBIS BOREALIS. 
1910. Spirorbis borealis, Southern. Proc. Roy. Irish Acad., vol. xxvin, p. 243. 
Elwes. Journ. M. B. A., vol. ix, p. 66. 
7 33 3) 3: 
N@IUL. ,»  Ditlevsen. Dan. Eksped. Gronl., Bd. v, p. 451. 
es . < Riddell. Proce. Liverpool Biol. Assoc., vol. xxv, p. 65. 
LOTO Fae Rs Wollebek. Skrift. vidensk. Krist., Bd. 11, No. 18, p. 115, pl. xliv, fig. 6. 
1913. 55 e Stephenson. ‘Trans. Roy. Soc. Edin., vol. xlix, p. 807. 
1914. #5 spirorbis, Southern. Proc. Roy. Irish Acad., vol. xxxi, No. 47, p. 148. 
neehy 5 borealis, Fauvel. Camp. Scient. Monaco, Fase. xlvi, p. 334. 
1915. a ee Allen. Journ. M. B. A., vol. x, p. 644. 
OWE a - Rioja. Anél. Poliq. Cantéb., p. 82. 
s ms s Borg. Zool. Bidr. Uppsala, Bd. v, p. 22, text-figs. 5—11. 
1919. 53 5 Horst. Zool. Mededeel. Rijks Mus. Leiden, Deel v, p. 3. 
Habitat— Abundant on the Fuci in tide-pools and on the rocks between tide-marks, 
as well as on Laminariz, St. Andrews (H. M.), and in similar places on Fuci and Laminarie 
all round the British shores. Large examples also occasionally occur on stones in rock- 
pools, St. Andrews. Small specimens are found on dwarfed Fuci under stones in tide-pools 
in Guernsey and Herm. Shetland, on limpet; Torquay (Elwes); Laneland Bay, Wey- 
mouth (J. G. J.); Plymouth (Allen); Firth of Forth (Leslie and Herdman, Cunningham 
and Ramage); Howth, Dublin and West Coast of Ireland (Southern). 
Klsewhere it has been met with in Greenland (Michaelson, Ditlevsen); Finmark (Norman), 
off Norway, 300 fms. (Sars); shores of France (De Quatrefages, De St. Joseph, who states that 
it is rare, on stones) ; Shores of Cantabria (Rioja) ; Atlantic Coast, U.S.A. (Verrill, Webster 
and Benedict) ; Spitzbergen (Fauvel); Falkland Islands (Pratt) ; Canada (Whiteaves). 
The collar is open as usual in the mid-dorsal line, but continuous ventrally, and it joins 
the alar membrane of the anterior setigerous region, which De St. Joseph has occasionally 
found of a bluish tint. The membrane passes ventrally behind the last bristle-tuft and 
fuses with that of the opposite side. At the base of the branchiz are two minute eyes on 
the dorsum. 
The branchiee and anterior region are pale; the stomach forms a dark opaque part, whilst 
the posterior region 1s marked by bands of reddish pigment-granules in each segment, the 
tip of the tail being pale. Beneath the cuticle and hypoderm of the branchial filaments 
is a layer of closely arranged parallel bars, apparently of a chordoid nature, which may act 
as a skeleton for them. It becomes thinner at the terminal process, which at the tip is 
shehtly bulbous, with a special arrangement of cells, somewhat after the manner of Filograna, 
but on a smaller scale and less distinct. Similar chordoid tissue of a modified kind also 
occurs in the pinnules, forming wider blocks ; yet this aspect may be due to the contraction 
of the hypodermic tissue, though this is unlikely, smce squares are seen on each side of the 
central cavity in life and when fully extended. An afferent and an efferent vessel 
pertain to each branchial filament, and the greenish blood seems to tinge the pinnules, 
which are richly ciliated. 
The branchie (Plate CX XII, fig. 10a) are four on each side, each filament having a 
short, slender, and slightly tapered terminal process, and bearing from sixteen to twenty 
pairs of rather long, ciliated and nearly cylindrical pmne, which do not arise quite opposite 
each other. Their colour is dull yellow, with a tinge of green from the blood-vessels. They 
are sensitive organs, receding with a jerk into the tube on being touched. 
