Genus 8. IDALIA,* Leuckart. 



Corpus ovatum, crassum, antice declive, postice acuminatum, vix palliatum. Caput subinferius, 

 subincrassatum, non tentaculatum. Tentacula 2 dorsalia, linearia, lamellata, non-retraetilia. Area 

 dorsalis cirris margiuata. Branchiae plumosse, in linea media dorsi anum cingentes. Apertura 

 genitalis ad latus dextrum. 



Idalia is a well-marked genus, characterised by Leuckart in 1828, in a small publication 

 entitled ' Breves Animalium quorundam maxima ex parte marinorum Descriptiones.'t 



The genus is distinguished from Triopa and JEuplocamus, with which Dr. Philippi has 

 confounded it, by its less destinct cloak, which forms a small dorsal area, not extending 

 beyond the tentacles in front, and leaving a considerable space between it and the frontal 

 margin of the head : the tentacles too are without sheaths, and the filaments which adorn the 

 pallial margin are generally very long in front of them. These characters likewise distinguish 

 it from the other allied genera. 



The prevailing colour in Idalia is red. Its range appears to be pretty extensive, and, 

 though nowhere common, members of the genus are found in most of the European seas. 

 They chiefly live in deep water, and hence, perhaps, the infrequency of their occurrence. 

 They are carnivorous. 



The body in this genus is ovate, thick, and a good deal elevated on the central area of 

 the back, from which it slopes down on all sides, especially in the frontal region, which is 

 large and incrassated. The head is indistinct, broad, and subinferior, with a slight expanded 

 margin above. There are no oral tentacles. The two dorsal tentacles are generally slender 

 and linear : they are laminated,— sometimes only slightly and on the posterior side. The 

 base of each is adorned with one or two filaments, which have sometimes been taken for 

 additional tentacles. These are not attached to the tentacles themselves, as in Ancula, but to 

 a thin and rather inconspicuous membrane — the margin of the rudimentary cloak — that 

 circumscribes the dorsal area, passing close to the base of the tentacles in front, and running 

 along each side of the back to the branchiae. This margin is more or less fringed with 

 filaments ; the inclosed area has also frequently one or more rows of filaments. The branchiae 

 are plumose, and surround the vent on the posterior dorsal line : behind these a ridge runs 

 down to the tail. The foot is broad, thick, and rounded in front. The aperture of the 

 generative system is on the right side. 



Idalia may be divided into two sections, differing from each other in the armature of the 

 month, as well as in the following external character. 



Section 1. Centre of the back with filaments. Type, I. elegans. 



Section 2. Centre of the back without filaments. Type, I. aspersa. 



Our observations on the internal organisation of this genus will have to be confined to 

 that of /. Leachii, as this is the only species we have had the advantage of dissecting, and 

 we are not aware that any description of the anatomy of the other forms has been 

 published. We have, however, examined the lingual apparatus of four or five kinds. 



* A name of Venus, from Mount Idalium, in the Isle of Cyprus, sacred to that goddess. 

 f We are indebted, for a copy of this publication, to Dr. Riippell, of Frankfort. 



