XXXIX.—On a Reversed Species of Fusus, (Fusus retroversus.) By the Rev. JOHN FLEMING, D. D. F. R. S. E. (Read 5th April 1823.) IT is well known to British conchologists, that sinistral, or reversed spiral shells, are of frequent occurrence among the terrestrial and fluviatile mollusca, while they are seldom to be met with among those which inhabit the sea. Extensive genera, indeed, occur in the former groups, in which all the species exhibit reversed whorls, not as a monstrosity, but as a permanent feature. The genera Clausilia and Vertigo, in the terrestrial, and Physa, Aplexa, and Planorbis, among the aquatic pulmonifera, are striking examples, and embrace about twenty indigenous species. Among the marine spiral shells belonging to the branchiferous mollusca, those with sinistral whorls are of such rare occurrence, that not more than one species in a genus has yet been detected. In the British Fauna, only two species have hitherto been recorded among the recent kinds, viz. the Murex adversus and Voluta heteroclita, of MONTAGU'S "Testacea Britannica." The addition, therefore, of a third reversed species, cannot fail to interest the British conchologist. The following description, with the accompanying magnified drawing, (Plate XV. fig. 2.), which exhibits a front and back view, will, we trust, sufficiently establish its characters. Shell with five rounded whorls, well defined at the line of junction. These increase somewhat rapidly in size, and, being a little depressed, give to the shell what is termed a bellied appearance. The mouth is oblong, placed obliquely, and interrupted by the convexity of the body-whorl. The outer lip joins the body-whorl at an acute angle. The pillar is straight, and slightly scooped out at the apex for the canal, which is shallow, regular, and short. The whole shell is smooth, glossy, and so transparent as to permit the pillar to be distinctly perceived throughout its whole length. The layers of growth are scarcely perceptible even when highly magnified. The whole shell scarcely exceeds a line in length. Three specimens of this shell have occurred to us in shell-sand from Noss Island, Zetland, which we collected after a storm in the spring of 1809. None of the characters of this shell would lead us to consider it as the young of any of the larger species. The relative proportion of the different whorls, and their number, intimate that the shell is nearly at its full growth, or, at least, that it has assumed its true form. Had any doubts remained on this subject, we would not have offered the preceding description, as we are aware, that fry of several shells hold the rank of species in the systems of British conchologists. This shell belongs to the section of the genus Fusus distinguished by the absence of a pillar-cavity, and which is known to include the Murex despectus and corneus of British writers, as examples. In this section, it will form a group along with the Murex contrarius of SOWERBY'S Mineral Conchology, vol. i. p. 63. tab. xxiii., distinguished by the whorls being reversed. Perhaps they might constitute a new genus, to be denominated Heterofusus. The Murex contrarius (now before me), which is found in gravel-pits in Essex and Suffolk, and which is considered as extinct, differs from the recent one, which we have described, in size, and in the shape of the whorls, the mouth, and the pillar. Our species, indeed, acquires considerable interest from this circumstance, that it is the only known representative of a tribe, inhabiting our seas at present, the Murex contrarius having probably flourished when the seas of Europe were peopled with a different series of molluscous animals. MANSE OF FLISK, XL.-Notice of a Specimen of the Larus eburneus, or Ivory Gull, shot in Zetland; and further Remarks on the Iceland Gull. By LAURENCE EDMONDSTON, Esq. (Read 8th March 1823.) LARUS EBURNEUS. I AM not aware that any individual of this very beautiful species has been hitherto noticed as occurring on the British coasts. The specimen now exhibited to the Society was killed in Baltasound, Zetland, on the 13th December last. It was remarkably lean, weighing only 10 ounces. The length is 16 inches, the breadth 3 feet 3 inches. The irides are stated by many ornithological writers to be brown; by others, as FABRICIUS, black: in this individual, however, they were of a pale lead colour. The bill is bluish-black at the base, gradually becoming paler towards the point. Feet and legs black; four toes, the hind one being very distinct: claws black, large, and tolerably sharp and hooked. The tibia naked a little above the knee. The skin is throughout covered by a profusion of remarkably thick, fine white down. The ground-colour of the whole plumage is of a delicate glossy ivory-white (as the name indicates), with brownish-black circular spots dispersed through it; these are very sparingly distributed on the back and lower part of the body; most numerous on the wing-coverts and scapulars: the tail and primaries tipped with the same colour: the throat is mottled in a similar manner: the dusky spots are, however, of a paler shade, running more into each other. The forehead and space between the eyes and bill, lead-colour. The tail consists of only eleven feathers, but this may be accidental. Its sex was very distinctly male; and I should be disposed to consider it a bird of the second year *. This species in its adult summer-plumage is of a snowy whiteness, and in this state has been often and accurately described by many naturalists. I do not, however, find any account of its winter-dress, or whether, during that season, it assumes a similar change of colour about the head as its congenerous species. FABRICIUS, in his Fauna Grænlandica, states, that it generally keeps out at sea, seldom approaching the land; "et tunc admodum incautus, ut facile occidatur." It is little fastidious in the selection of its food, and very voracious, feeding chiefly on carrion. The voice is harsh and strong. The mode of breeding seems not to have been ascertained. It is peculiarly an arctic bird, inhabiting chiefly Spitzbergen, and the highest northern latitudes. It is peculiarly * MEYER describes a second year's bird having the characters here stated. MEYER'S specimen, however, was killed in March.-EDIT. |