IDALIA ELEGANS. 



which his description was taken, however, was not half the size of ours, and appears to have 

 been less brightly coloured; the branchial plumes were also proportionally smaller, which may 

 have arisen from its being a young individual. We think that we likewise recognise in our 

 animal the true Idalia elegans of Leuckart; although his description, having been taken from a 

 dead specimen, is deficient in some of the points necessary for comparison. The characters 

 agree in every thing as far as they go. The number of branchial plumes is greater in this than 

 in any other species of the genus. Leuckart makes them, 18-20,' and according to our own 

 observation the real number is eighteen, though from two of them being bifid, they exhibit 

 twenty points. One or two of the posterior ones are very inconspicuous, and may readily be 

 overlooked. 



Well indeed does this Idalia merit the name of elegans ! It is certainly the most beautiful 

 of the tribe we have met with. The orange of the filaments is so brilliant as to defy the power 

 of the painter, and the delicate rose-colour of the body, in the individual from which our 

 drawing was taken, added much to its attractions. A second specimen had the colours a 

 little darker. 



This valuable addition to our Fauna was dredged in the summer of 1853, near Castle 

 Cornet, in Guernsey. From a curious habit, hitherto unknown in this tribe, of concealing itself 

 in the test of an Ascidian {Cynthia tuberosa), it escaped observation on being taken from the 

 dredge, and was put into our collecting-box as an Actinia partially expanded. On examining 

 the contents of the box in the evening, we were delighted to find we had got a beautiful Idalia, 

 which had crept so far out of its place of concealment as to display its true form. A second 

 individual was afterwards found amongst the contents of the box, with only its head and 

 anterior filaments protruded from the test of another Cynthia of the same species. This was 

 put into a glass of sea-water over night untouched, to allow it to creep out without injury : but 

 in the morning it was found inhabiting the same cavity, from which it had not made any 

 attempt to escape, and it required a gentle pressure of the Ascidian to disengage it. From 

 our desire to get a drawing of the Nudibranch in a fresh state, we neglected to examine the 

 Ascidian more carefully, in order to ascertain the nature of the connexion between them. 

 The cavity from which it emerged appeared to be similar to those made by the Modiola 

 marmorata, which is frequently lodged in the test of this Cynthia, and the Idalia may therefore 

 have entered it to prey upon the mussel ; but it is a curious circumstance that both the 

 specimens taken should have been so lodged, and with the head outwards ; seemingly indi- 

 cating a habit of remaining concealed in such a situation, which the reluctance to quit it also 

 seemed to imply. 



Figs. 1 , 2. Side and back views of Idalia elegans. 



3. Two brachial plumes, much enlarged. 



4. Front view of tentacle. 



