reaohes the length of 50 mm. A general structural description follows, and he points out
the essential differences of the dorsal lamellae in the three species.. Bifid dorsal bristles
.only are present in S. miniaceus, while in the other two simple bristles accompany the
former. . The mouth opens on the ventral-'surface anteriorly, and four small brown eyes
lie at the base of the tentacle, each with a short thick nerve from the Cephalic ganglion.
The nerve-cords are. separate except for the transverse commissures. The alimentary
canal consists of fore, middle, and hind gut, besides cmcal appendages. The pharynx is
muscular. The mid-gut possesses generally a pair of diverticula in each segment, and
terminates in an anus which has a pair of short cirri. Excretory organs are absent, but
a blood-system is present. There are no differentiated branchim. The reproductive
elements are separated from the body-wall, and lie in the body-cavity. All are parasitic
on sponges.
Recently Racovitza1 (1896) has carefully investigated the structure and homologies
of the cephalic region, and he is of opinion that only the sincipital region of the head
remains with the tentacle and the four eyes, and the much reduced brain internally; the
latter (brain) consisting of the middle region only, whereas in Eurythoe and Euphrosyne
both the anterior and posterior regions of the brain are present. This reduction of the
cephalic region he attributes to parasitism on Esperella and other sponges.
The species show a certain amount of variation, and von G-raff thinks that the somewhat
radiate arrangement of the parts anteriorly and posteriorly approaches the condition
in Myzostoma, which occurs on starfishes, while Spinther frequents sponges.
In the pinnate arrangement of the alimentary cmca Spinther differs from the typical
Euphrosynina, and approaches the Aphroditidm.
1. Spinther onisooides, Johnston, 1845.
Specific Characters.—A dorsal cirrus at the end of the parapodium.. The dorsal
lamellae project at the free margins and have a series of strong, simple or bifid bristles.
The hooks of the parapodia are powerful, pectinate at the projecting margin, and the tip
is strongly curved. Ventral surface furnished with small papillae (warts) on the ridges
which flank a median furrow. Posterior end split to the anus.
S yno nyms.
1845. Spinther onisooides, Johnston. Ann. Nat. Hist., vol. xvi, p. 8, pi. ii, f. 7_14.
1854. Cryptonota citrina, Stimpson. Marine Invest. Grand Manan, p. 35, pi. ii, f. 27.
. 1865. Spinther onisooides, Johnston. Cat. Brit. Mus., p. 127, pi. xiv, f. 7__14.
1882. „ arcticus, Hansen. Annel. Norsk. Nordhavs-Exped., p. 44, pi. i, f. 1—5.
1883. ;, major, Levinson. Syst. Oversigt. nordiske Annulata, &'c, Vidensk. Meddelels, p. 125.
1887. „ - omscoides, Graff. Zeitsch. f. w. Zool., vol. xlvi, p. 90, pi. vi—viii, and woodcuts.
Habitat.—Dredged off Oastle Chichester, Belfast Bay, by Mr. Hyndman in 1844,
an d off Anglesey in seventeen fathoms (Homell) ?(fide Dr. A. Merle Norman). Abroad
1 | Arch. Zool. Exper.,’ 3 ser,, vol. iv, p. 197, &c., 1896.
it has been met with in the Bay of Fundy, New Brunswick, by Stimpson and Leidy, and
at Station 275 (Ost Ha vet) den Norske Nordhavs-Expedition 1876-8 (Hansen). Verrill
includes it in his list of marine forms from Cape Cod to the St. Lawrence.
Body.-^Length 11 to 26 mm., the British forms seen by Johnston approaching the
first-mentioned figure, ovate or somewhat oblong, convex dorsally, smoothly rounded at
each extremity. The more convex dorsum has a series of symmetrical double lamellae,
strengthened by simple or bifid bristles, the tips of which slightly project beyond the
skin, these lamellae being continuous with the feet, which in Von G-raff’s example amounted
to forty-eight, Johnston’s specimens, apparently having fewer. The ventral surface has
a series of low ridges studded with minute warts, the anterior sloping forward and the
posterior backward, the middle line being marked by a furrow, likewise warty. In the
largest example (26 mm.) the thickness in the centre of the body was 2‘5 mm., thinning
off at the sides, and the breadth about 11 mm.; the height of the dorsal lamellas in the
same being 1*5 mm. The anus terminates some distance within the posterior border, the
adjoining pair of ventral ridges presenting no special differentiation.
Colour.—Johnston’s examples were of a uniform cream-yellow colour, while Von
Graff’s had a yellowish-ochre hue. Stimpson observes that his specimen was of a
beautiful lemon-yellow colour, resembling very much that of some sponges occurring
with it on a gravelly and muddy bottom in thirty-five fathoms in Hake Bay, Grand
Manan.
Head.—This region is merged into the general contour of the body, but bears
superiorly over the brain the ridge-like dorsal tentacle with four eyes at the base. The
mouth opens on the ventral surface some distance behind the anterior border, often 4s a
radiate button—from the protrusion of the proboscis.
Feet {parapodia) .—These are distinguished by the possession of a ringed base, and
the presence of a short dorsal cirrus of about four or five segments, the lamellar ridge of
the dorsum curving smoothly away from it on the one hand, while on the other the
golden hooks emerge near its base ventrally. The hooks, which are excellently figured
by Von Graff,1 have strongly curved and sharp points, while the terminal process of the
shaft is boldly serrated. One or two of these project freely, while internally one or two
are in course of development, the point appearing first, according to Von Graff, in a
cellular matrix.
I t is remarkable that, notwithstanding the great increase of zoological explorations
of the British seas, no example of this species has been procured since Dr. Johnston
described it, with fair accuracy—both with regard to external form and the characters of
the bristles and hooks—from two examples forwarded by Mr. Wm. Thompson of Belfast.
Moreover, Prof. Jeffrey Bell informs me the type specimens cannot be found in the
British Museum. Under these circumstances the only alternative was to utilise what
had been so ably written by Von Graff and others, and place materials for ready
identification in the hands of future observers..-
The species follows the habit of certain marine forms, adhering to sponges and
feeding on them, so that the alimentary canal, including the dorsal blind sac, is packed
with sponge-debris and spicules.
1 Op. cifc., pi. viii, figs. 4 and 5.