Abbildungen der Seite
PDF
EPUB
[ocr errors]
[ocr errors]
[ocr errors]

ART. V. Illustrations in British Zoology. By GEORGE John

ston, M.D., Fellow of the Royal College of Surgeons of Edinburgh.

22. TE'RGIPES PU’LCHER. ( fig. 59.) Cl. Gasteropoda, Ord. Nudibránchia, Fam. Glaúcidæ. The Térgipes is a naked sea snail with external branchiæ disposed in two series, one along each side of the back; they

are of a cylindrical form, and it is supposed that the apex of each forms a little sucker by means of which the animal can fix itself to the stalks and fronds of seaweed, and walk upon its back. Rang is of opinion

that this fact reTergipes pálcher : a, natural size; b, magnified.

quires new obseryations to assure us of its certainty; and the species about to be described never performed any such remarkable feat during the few hours it was preserved.

One species (Doris maculàta Montagu) has already been described as a native of the coast of Devon, but it differs in so many particulars from ours, that some may deem it necessary to arrange them in separate genera, and we, at all events, may be spared the necessity of elaborating a comparative description to prove their distinctness. Térgipes pulcher was found in Berwick Bay, upon a piece of wood brought up by the line from deep water : its motions were slow and gliding, like the rest of its tribe; but, unlike the greater number of these, it was ornamented with spots of such warm and brilliant colours, that it might possibly have attracted the notice of even those who wonder very much what there is in a snail that it should have admirers.

Térgipes púlcher is half an inch long, ovate, soft, white, ornamented with scarlet tubercles scattered over the back, and with short cylindrical processes tipt with bright orange arranged round the sides : mouth subinferior, terminal, with a linear-oblong membranous tongue, set with minute prickles in close transverse series : tentacula two, dorsal, non-retractile, short, oval, imbricate, orange-coloured : back even, studded with many scarlet unequal tubercles, some of which, when

[graphic]
[graphic]

magnified, appear ocellated: towards the tail are three short white processes placed in a line across the back, which are not retractile; and there are eighteen short obtuse branchial processes placed on the margins, the smallest in front, and all tipped with orange; the apices, perhaps, conformed like suckers: foot oblong, with plain margins: aperture of generation lateral and anterior. When viewed through a magnifier, this pretty mollusc has a roughish or flocculent appearance. The cloak contains numerous calcareous spicula interlaced in every direction, the spicula of unequal sizes, curved, with a sort of knob in the centre, whence it tapers to each end, the points of some of them being forked. The latter sort are abundant in the branchial processes, and the forked end is always pointed outwards. The specific character may be thus expressed:— Térgipes pālcher. Corpore ovato, albo, supra tuberculis coccineis notato; tentaculis duobus, ovatis, imbricatis, aurantiis; branchiis brevibus, apice aurantiis.

[ocr errors]

OUR figures of this remarkable production are taken from a dried specimen, with the loan of which I was favoured by Mr. Bean of Scarborough. It incrusts a univalve shell,

Spóngia suberia, of the natural size.

apparently the Türbo crássior, and entirely covers it. The zoophytical crust is thin and uniform, and no pores or faecal orifices are visible on the surface, but the processes are hollow, and their walls, which are smooth and alike on both surfaces, appear to be perforated, in a longitudinal direction, with a circle of small canals which probably open on the rim of the process; but this structure is rather inferred from the appearance presented by the spot from which a process has been broken, and from an obscure vestige of pores on the rim, than from dissection, and remains, therefore, open to correction. The sponge is apparently composed of fine particles of sand closely compacted, and is of a uniform grey or stone colour; the surface is even and smooth, but large papillary processes, from one to six lines in height, cylindrical and tubular, rise up irregularly from it, the apices of which are circular, cupped,

[graphic]

anive that ongement le betwendea Tour its Occiosity of less

with a thick somewhat inflected and plaited rim. Where the sponge incrusts the shell it is thin, but the tubular processes are between two and three lines in diameter, and, when removed at the base, they leave a mark exhibiting a circle of cells radiating to the outer edge.

I am of opinion that this is the Spongia suberia of Moctagu (Wern. Mem., i. 100.), in a perfect state. Mootagu seems to have met with specimens only previous to their production of the tubular processes, and, if we subtract these from our description, it will be found to correspond in other respects with the description of this excellent observer. He says that the “ sponge is of a corky nature, resembling the close texture of the stalk of some species of Boletus. It has rarely any other pores than what are formed by the fibres, which are so extremely fine, as not to be visible to the naked eye, even when broken; and with the assistance of a pocket lens, they are not definable on the surface. Its colour is orange-yellow when fresh, becoming brown when dry: its shape is indefinite, but it has the singular property of being attached only (as far as I have been able to ascertain) to old univalve shells, which it entirely invests. It is also remarkable, that few instances occur where the hermit crab has not formed a lodgement in the nucleus shell, and there appears to be a great struggle between the two parasitical intruders, as the sponge is continually endeavouring to fill up the aperture of the shell, while the crab, by its occasional motion in search of prey, frustrates that natural propensity of the sponge. Notwithstanding the efforts of so active and restless an intruder, the gradual and insensible increase of the sponge gains upon the premises of the crab; it pushes it on all sides, and completely lines the interior surface of the shell, so that the crab soon finds its habitation too small, and is compelled to search for a more capacious house."

Dr. Fleming has placed this sponge in his genus Halichondra (Brit. Anim., p. 522.), distinguished from the other genera of the family by the siliceous spicula which enter so abundantly into its organisation; and he says that the spicula of the species in question, which he has found " incrusting corallines in the Frith of Forth,” are fusiform and slightly curved. Montagu makes no mention of these spicula, which probably require a high power of the microscope for their detection, and hence they also escaped my observation. To any correspondent of this Magazine I should feel much indebted by the communication of specimens of the Spóngia subèria, either dried or preserved in spirits.

Berwick upon Tweed, June 12. 1834.

ART. VI. Fusus Turtdni Bean, and Limnèa lineata Bean, Two

rare and hitherto undescribed Species of Shells, described and illustrated. By WILLIAM Bean, Esq.

Fo`sus Turtòni Bean. (fig. 61.) — Shell fusiform, covered with slightly elevated spiral lines broader than the intervening

spaces, and crossed by numerous longitudinal lines of growth. Length 41 in., and about 2 in. broad; volutions 9, a little raised in the middle, from which they gradually slope to the separating line; aperture ovate, nearly of the same length as the spire; canal wide and short; outer lip a little dilated and very thick; inner lip smooth, glossy, and much spread on the pillar. Colour white, covered with a brown epidermis, and the inside pale violet.

This noble and probably unique shell we have named after our old and esteemed friend, Dr. Turton. It was found among the rejectamenta of a boat at Scarborough, and is one of the “ great guns” of our collection, which

contains (we say it prouda, Fusus Turtdnd; , its operculum. ly) 1050 species and varieties, and above 50,000 specimens of genuine native shells.

Limnèa lineata Bean. (fig. 62.)— Shell oblong-ovate, subventricose, with about 12 long and short (often forked)

raised transverse lines on the body whorl, giving it an angular appearance crossed by numerous longitudinal striæ.

Length of the largest spe4, Limnéa lineata ; b, reversed variety.

cimens 6 lines, breadth 4

[graphic]

lines; volutions 4; spire short and acute; aperture ovate; outer lip thin; inner lip reflected, forming a small hollow behind it.

This remarkable shell is only found in one pond in our neighbourhood; and the reversed variety is of rare occurrence. It differs from our specimens of L. péreger in being thicker and stronger; is of a darker colour, and only half the size: it is certainly very like some of the numerous varieties of this shell, yet most of our scientific friends agree with us in considering it specifically distinct. The raised lines on the body whorl are very variable: in some specimens they are nearly obliterated; but in very few instances are they wholly wanting. Mr. G. B. Sowerby, in his Genera of Recent and Fossil Shells, united Physa, Myxas, and Apléxa to the genus Limněa. He says, “the only describable difference in the shells, except mere specific differences, consists in the Apléxa and Physa being heterostrophe shells, while the Limnéa and Myxas are dextral. The reversed Limněa found at Scarborough will certainly prove the correctness of Mr. Sowerby's views.

Scarborough, July 30, 1834.

ART. VII. A List of some Land and Freshwater Species of Shells which have been £g. in the Neighbourhood of Henley on Thames. By H. E. STRICKLAND, Esq.

I send you a list of land and freshwater shells which I found, some years ago, in the neighbourhood of Henley on Thames, a district which furnishes a greater number of species than any other with which I am acquainted. This is doubtless owing to the diversity of hills and valleys, wood and water, which adorn that charming neighbourhood, and supply to each species an appropriate habitat. I have thought it best, in the case of the more rare species, to state exactly the locality or situation where each occurs; as, without this knowledge, a conchologist might search for them a long time without success: v r mean very rare; r, rare; f, frequent; C, common.

Mollásca Gasterópoda Pulmonffera Terrícola. —Cyclástoma €legans, beech woods, f. Carocólla lapícida, adhering to beech trees, f. Helix aspérsa, c.; nemoralis, c, horténsis, f; arbustörum, moist plantations, r, ericetorum, dry chalky banks, c : virgāta, f; caperāta, f. ruféscens, c; hispida Drap. (not of Montagu), c; cantiana (Carthusiana Drap.), hedges and plantations, c, fūsca, Fawley Woods, or; alliaria, damp

« ZurückWeiter »