iv A MONOGRAPH OF THE 



(10) Thecacera virescens. 



Thecacera virescens, Aid. and Hanc, in Ann. Nat. Hist., 2d ser., v. 8, p. 290. 



Body rather convex, smooth, and of a light peach-blossom tint, blotched with green 

 anteriorly and posteriorly. Head with a plain margin in front. Tentacles broadly laminated ; 

 the laminated portion green, the lower or smooth portion of the same colour as the body: they 

 are retractile within moderately sized sheaths, with smooth margins. Branchial plumes five, 

 green, margined with white. A single row of obsolete tubercles encircles the branchial region. 

 Foot of a dull yellowish- white. Length three tenths of an inch. 



This description was drawn up from two individuals sent us in spirits by Mr. W. P. Cocks, 

 of Falmouth, assisted by his notes and drawings of the animal in a living state. The specimens 

 were found by Mr. Cocks, at low-water mark, on the oyster bed at Bar Point, Falmouth, in 

 March, 1849. 



(11) Thecacera capitata. 



A few specimens of this new Thecacera were dredged in twenty fathoms water off St. Ives, 

 Cornwall, in September, 1853, by Mr. Barlee, who kindly presented two of them to us. The 

 larger specimen was nearly colourless when it reached us (in spirits), but had the orange 

 tubercles very distinct : there were four or five on each side of the veil, and a row of four 

 between the tentacles ; besides which there was a row of smaller tubercular orange spots on 

 each side of the body below the veil ; and a central and two lateral rows of obscure yellowish 

 tubercles reached from the branchiae to the tail. The veil was continued in a slight pallial 

 ridge backwards, dying out before it reached the branchiae. The smaller specimen was 

 darker and more distinctly freckled, but the orange colour of the processes was gone. In this 

 specimen only two tubercles were observed on each side of the veil. 



The last two species differ considerably from the first, which must be taken as the type of 

 the genus Thecacera, but the sheathed tentacles sufficiently unite them to allow of their being 

 placed in the same genus. 



(12) ID ALIA ASPERSA. 



Idalia cirrigera, ' Phil./ Loven, Ind. Moll. Scand., p. 5. 



Professor Loven, who considers that the number of filaments is variable and does not 

 afford a specific character in this genus, has united our I. aspersa with the /. cirrigera of 

 Philippi. In this he is certainly mistaken. We have recently had an opportunity of 

 examining several specimens of this rare genus, and find the number of filaments in each 

 species to be pretty constant : a slight variation undoubtedly occurs, but this is seldom of such 

 importance as to leave any doubt of the species to which the individual belongs. The 

 Scandinavian species, a drawing of which we have seen, appears to be a variety of our 

 I. aspersa. In our description of this species we have stated the number of branchial plumes 

 to be twelve : a more careful examination has satisfied us that the real number is only ten, 



