POLYDORA CAKCA. 485 
1893. Polydora flava, Carazzi. Mitt. Zool. Stat. Neapel., Bd. xi, p. 22, pl. ii, figs. 9 and 10. 
‘ fl » Lo Bianco. Atti Accad. Sc. Nap., ser. 2, vol. v, p. 31. 
a es ceca, Mesnil. Comp. Rend. Acad. Se. Paris, p. 643. 
1894. a » De St. Joseph. Ann. Sc. nat., 7° sér., t. xvii, p. 50, pl. iii, figs. 65—70. 
»,  Leucodore ,, Hornell. Nature, vol. xlvii, p. 78. 
1896. Polydora ,, Mesnil. Bull. Sc. France Belg., t. xxix, p. 191, pl. xii, figs. 23—29. 
1914. a » Southern. Proc. Roy. Irish Acad., vol. xxxi, No. 47, p. 103. 
Pe - » Fauvel. Annél. Polych. Monaco, p. 219. 
1915. *f » McIntosh. Ann. Nat. Hist., ser. 8, vol. xv, p. 3. 
es A » Allen! Journ, M. B: Bop vol. x, p. 630. 
1920. - » Hliason. Polych. Oresund, p. 46, text-figs. 12 a—e. 
Habitat—Specimens kindly forwarded by Southern from Blacksod Bay, Ireland; shore 
collection, Plymouth (Allen). 
It occurs in Norway (Cirsted); Mediterranean (Lo Bianco) ; shores of France, in tubes 
on oysters (De St. Joseph), and under Lithothamnion (Mesnil) ; Farde (Willemoes-Suhm) ; 
Arctic Sea, Swedish waters (Hliason). 
The head is similar to that of Polydora flava, with a bifid median process, which is 
continued backward as a keel to the second segment, whilst the broad peristomial lobes 
support it laterally. The long tentacles have a deep, ciliated groove and readily fall off. 
The body reaches 20 mm. in length, has from fifty to ninety segments, and terminates 
posteriorly in a sucker. It is colourless, or slightly yellowish. The second, third, fourth 
and sixth segments have a short cirrus and a tuft of simple winged bristles (Plate CX XXVIII, 
fig. 106). The fifth segment has strong acicular bristles or hooks (Plate CXXXVIII, fig. 
10), with a distinct hook at the tip, but, as in P. flava, no spur. The tips of those hooks in 
the tissues are sharp, whereas those exposed are blunt. The concavity of the hook further 
shows in lateral view a double outline as if a flattening or hollowing of the surface were 
present. This is observed even in the developing forms, where only the tip exists, and is 
therefore an original character. It bears as usual a dorsal and a ventral tuft of capillary 
winged bristles. 
Along with the powerful acicular bristles are minute oar-shaped forms (Plate CX XX VIII, 
fig. 10a) with short, delicately pointed tips. The seventh segment has glandular pouches 
and a dorsal branchia, and whilst the winged capillary bristles continue dorsally (Plate 
CXXXVI, fig. 9), hooks occur ventrally. Moreover in the seventh, eighth and ninth 
segments and the last three is a simple bristle much longer and finer than the ordinary forms. 
The branchize continue to the fifty-eighth segment in an example with ninety-eight segments 
(De St. Joseph). The glandular pouches cease from the thirteenth to the fifteenth segment 
(De St. Joseph). About the twenty-filth segment, in front of the sucker, stout acicular 
bristles appear in the dorsal tuft, and continue almost to the tip of the tail, and this feature 
and the comparative strength of the bristles (Plate CX XXVIII, figs. 10 and 10a) of the 
region generally make a contrast with those of Polydora ciliata, where they are both very 
long and very slender. Mesnil observes that they are less developed than those of P. Giardi. 
The bristles of the posterior region, mdeed from the fiftieth segment backward, are 
distinguished by their great strength and comparative shortness. Several of the shorter 
in each tuft terminate a little beyond the skin in stout, pointed tips like spmes. In many 
