TRANSACTIONS OF THE SECTIONS. 73 
being large in the British, and extremely small in the Mediterranean Sagitta. From 
the latter the following points of structure were made out. On each side of the head 
is a row of curved bristle-like processes, wnich can be erected or depressed at the 
will of the animal. On the head are two distinct black eyes. The mouth opens into 
a straight intestine, terminating in a vent where the body begins suddenly to contract, 
at about two-thirds of its length. On each side of this vent, but opening on the op- 
posite side of the body, is a slightly curved canal, terminating in a cul de sac, and 
resembling closely the canals which contain the pinnated appendages of the Cydippe, 
but empty. The fins are of various shapes, and appear to form a sound basis for 
specific distinctions, They are rayed. The length of the largest specimen was two 
inches. The British examples were very minute. M. D’Orbigny has figured and 
described several species of Sagitta, which he observed during his South American 
voyages ; but the details of his observations do not exactly coincide with those of 
Professor Forbes, The body which D’Orbigny styles a heart was not seen by the 
latter in any case; and the only circulation observed was an obscure movement of 
fluid with granules in the posterior part of the body behind the anus. No appear- 
ances of cilia were seen on the external surface. The author concluded, that however 
anomalous the characters of these curious animals might seem, it was nevertheless 
convenient, and probably correct, to arrange them among the nucleobranchous mol- 
lusca. He proposes to name the Mediterranean form Sagitta Mediterranea, and the 
British Sagitta Britannica. To the same order he was inclined to refer the shell 
called, by Dr. Fleming, Fusus retroversus, and which appears to be identical with, or 
at least very nearly allied to, the Atlanta trochiformis of M. D’Orbigny. 
On some new Species of Mollusca nudibranchiata, with Observations on the 
Structure and Development of the Animals of that Order. By Messrs. 
J. ALDER and A. Hancock. 
The species described were a beautiful Calliopcea, the first discovered in Britain, and 
four new species of Eolis. The authors gave an account of their observations on the 
development of the ova in that order, stating the remarkable fact of these animals 
undergoing a complete metamorphosis, and being in their first or larva state, furnished 
with a nautiloid shell, which afterwards entirely disappears. They next alluded to 
some interesting anatomical peculiarities, describing the gastro-vascular system in 
Eolis, and the ejection occasionally of some curious bodies from the ends of the pa- 
pill, apparently connected with this system. The organs of the external senses were 
next remarked upon, and the existence of organs of hearing in this class of gastero- 
pods for the first time pointed out. They consist of small capsules filled with very 
minute concretions, which, in the living animal, are in a continued state of oscilla- 
tion. Several reasons were also adduced for supposing that the dorsal tentacula of 
these animals are the true organs of smelling. The whole was illustrated by a series 
of drawings by Mr. Hancock. 

Mr. Thompson noticed some additions to the Fauna of [reland, comprising alto- 
gether in the various classes (excepting Insecta, Entozoa and Infusoria) about sixty 
species. 

On the Irish species of the genus Limax. By the Rev. B.J.Cuarxe. Iilus- 
trated by coloured drawings and living specimens. 
Two species were described in detail which had not been included by previous 
writers in the British Catalogue, the Limax arboreus of Bouchard, and the L. Ga- 
gates of Draparnaud and Ferussac. The occurrence of both had been noticed by Mr. 
Clarke in the Annals and Mag. of Nat. Hist. for 1840, but with some doubt, which 
subsequent observations had removed. Of Limaz arboreus a minute detailed de- 
Scription was given, from which it would appear to be identical with the Limax so 
designated by M. Bouchard. But in the absence of specimens or figures for com- 
parison, Mr. Clarke suggested the name of L. glaucus, as descriptive of its very 
peculiar hue, if it should not prove to be identical. The ZL. arboreus is not un- 
common in the wooded districts of Ireland, especially on the ash and the beech, 
concealing itself during the daytime under the moss on the trunks. 
Limaz Gagates (Draparnand).—The Irish specimens of this Limax agree with 
