Fam. 2, Plate 3. 



TRITONIA PLEBEIA, Johnston. 



T. quadrata, supra fusco et fulvo liturata, subtus alba : velo integro, 8-mucronato : branchiis 5-6 

 utrinque, parvis, bipinnatis. 



Tritonia pleheia, 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. 



Bodij 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, occasion- 

 ally 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. 



