Pam. 2, Plate 3.
XRITONIA PLEBEIA, J o h n s t o n .
T. quadrata, supra fusco et fulvo liturata, subtus alba: velo integro, 8-mucronato: brancbiis 5-6
utrinque, parvis, bipinnatis.
Tritonia plebeia, Johns., in Edinb. New Ph. Journ. v. 5, p. 77.
Idem, in Ann. Nat. Hist. v. 1, p. 115, pi. 3, f. 3, 4.
Tritonia pulchra ? Johns., in Edinb. New Ph. Journ. v. 5, p. 78.
Hab. On Alcyonium digitatum and other zoophytes from deep water; common. Berwick Bay,
Dr. Johnston. Cullercoats and Newbiggin, Northumberland. Whitburn, Durham, Rev. G. C. Abbs.
Aberdeen, Professor Macgillivray. Cork Harbour, Professor E. Forbes. Rothesay Bay. Torbay.
Body upwards of an inch in length, oblong, quadrilateral, with nearly parallel sides,
truncated in front, and tapering to a point behind. Colour various, but generally of a pale
yellowish brown on the back, with darker brown markings; sometimes reddish brown,
greenish, or yellow, and frequently spotted with opake white. The dark markings are
strongest behind the tentacles, and generally form two irregular lines along the sides of the
back, interrupted and paler opposite each pair of branchial tufts. Oral veil entire and
nearly straight, sometimes very slightly notched in the centre; transparent white, occasionally
veined with purple-brown, and produced into about eight tentacular points. Tentacles
issuing from entire-edged cylindrical sheaths, columnar and transparent below, above rather
opake, generally yellowish, and surmounted by a fasciculus of branched filaments of nearly
equal length, excepting one placed towards the back, which is simple, truncated, stouter
than the rest, and extends beyond them. Back nearly flat, obscurely tuberculated,
angulated at the sides, but not produced into a waved pallial expansion. The sides
of the head are also angulated.’ Branchial tufts five or six on each side, small, erect,
bipinnate, frequently with a single lateral branch. The first and last tufts are small, the
others larger, and in old individuals there are occasionally minute intermediate ones. Sides
of the body nearly perpendicular, smooth, and more or less marbled or veined with purple-
brown on the upper part. Foot transparent white, the centre having a yellowish tinge from
the liver; it is rounded in front, and produced into a blunt point behind.
The heart beats 72 times in a minute.
This species, first noticed by Dr. Johnston, is distinguished from T. Hombergii
by its more squared and less depressed form, by the obscure pallial ridge, and by the
simpler form of. the branchiae, which in the young of the latter are more branched
and obtuse, spreading out from a foot-stalk on all sides, whilst in this species they have a
greater resemblance to those of the Doridida. The best character, however, is in the veil,
which in T. plebeia is entire, with seldom above seven or eight points, while in T. Hombergii
it is always bilobed and more produced, with numerous points.