Part 15

3. CUCULLÆA. Distant teeth oblique; posterior muscular impression prominent. Fig. 133.

4. PECTUNCULUS. Hinge curved. Fig. 134.

5. NUCULA. The same, with a pit in the centre of the hinge, including Myopara and Crenella. Figs. 135 to 137.

6. SOLENELLA. Fresh water, oval; a series of teeth on one side of the hinge, only two or three on the other. Fig. 138.

ARCHAIAS. Montf. A genus of microscopic Foraminifera.

ARCHONTE. Montf. HYALÆA, Auct.

ARCINELLA. Schum. CHAMA Arcinella, Auct.

ARCTICA. Schum. CYPRINA Icelandica, Auct.

ARCUATED. (Arcus, an arch.) Bent in the form of an arch, as Dentalium, fig. 2.

AREA. A flat space or disc, on any part of a shell. As for instance, the triangular space on the hinge of Arca, fig. 132, and Spondylus.

ARENACEOUS. (Arena, sand.) Of a sandy texture, as the sand tubes surrounding the bodies of some of the Annellides, named Arenaria on this account. But the word is more commonly used to intimate the habits of the animal, burrowing with its shell in the sand.

ARETHUSA. Montf. A genus of microscopic Foraminifera.

ARGONAUTA. Auct. Commonly called the "Paper Sailor." Fam. Pteropoda, Bl. Order Cephalopoda Monothalamia, Lam.--Descr. Light, thin, transparent or nearly so, symmetrically convolute, carinated by a double row of tubercles, terminating smooth or tuberculated ribs radiating towards the centre; aperture large, elongated; peritrême acute, interrupted by the body whorl.--Obs. The exquisitely beautiful, light and delicate fabrics included under the above name are inhabited by a molluscous animal named the Ocythöe, which is provided with tuberculated arms. These, hanging over the sides of the aperture, give to the whole the appearance of a vessel propelled by oars: a poetical illusion further heightened by the broad, flat membranes of the two arms, which, when vertically expanded, present an idea of sails. Pliny has described the Nautilus (the name has been changed by the moderns) as sailing gracefully on the Mediterranean waters; and Pope has versified the idea in the well known lines

"Learn of the little Nautilus to sail, Spread the thin oar and catch the driving gale."

Scientific men have long been engaged in the interesting discussion, whether the animal really belongs to the shell in which it is found, or whether, having destroyed the rightful owner, it has possessed itself of the "frail bark." It is now, however, proved beyond the shadow of a doubt that the Argonaut is the testaceous part of the Ocythöe, and that the broad membranes which in some representations have been artificially placed as sails, are naturally bent backwards over the shell like the mantle of some other molluscs. The interesting experiments of Madame Power, in the Mediterranean, have contributed very materially to lead the investigations of Naturalists to a satisfactory conclusion. This lady kept a cage under water, in which Argonautæ were bred in great numbers, giving her an opportunity of tracing the gradual development of the shell in all its stages, from the elastic and transparent nucleus to the full grown "Paper Sailor." Fig. 485.

ARIANTA. Leach. A sub-genus of land shells, containing HELIX arbustorum, Auct. (Gray, Turton, p. 137.)

ARION. A genus of slugs which have no shells.

ARROW-HEADS. One of the names by which fossils of the genus Belemnites were formerly known.

ARTEMIS. A genus of bivalve shells, distinguished from those of the genus Venus, by having a rounded, denticular form, and a deep, angular sinus in the palleal impression. This does not appear to me to be a sufficient ground of generic distinction, the palleal impressions of the Veneres being subject to great variations. British, also from West Indies, South America, Australia, &c. A. lincta, fig. 118.

ARTICULATED. (Jointed.) Applied to distinct parts of shells, which are fitted or jointed into each other, as the valves of Chitones and those of Balani. The operculum of Nerita is said to be articulated to the columella, having a small process by which it is as it were locked under the edge. See Introduction. The word is also applied to the Cirri, which protrude from the oral openings of Cirripedes.

ARTICULINA. D'Orb. A genus of microscopic Foraminifera.

ASIPHONIBRANCHIATA. Bl. The second order of Paracephalophora Dioica, Bl. Consisting of spiral univalves, which have no notch or canal at the anterior part of the aperture. This order is divided into the families Goniosomata, Cricosomata, Ellipsostomata, Hemicyclostomata, and Oxystomata.

ASPERGILLUM. Lam. (From Aspergo, to sprinkle.) Fam. Tubicolæ, Lam. Pyloridea, Bl.--Descr. The small, equal, equilateral valves are cemented into, so as to form part of, a large tube; the umbones are slightly prominent outside. The tube is elongated, rather irregular, granulated with sandy particles, and terminated at the base by a convex disc, which is perforated by small pores, elongated into tubes round the edge, presenting a resemblance to the spout of a watering pot, whence the name is derived. Loc. New Holland, Java, New Zealand, Red Sea. Fig. 44. Aspergillum Vaginiferum.

ASSIMINEA. Leach. Fam. Turbinacea, Lam.--Descr. Inclining to oval, light, thin, covered with a horny epidermis, spire produced into an acute pyramid; whorls slightly angulated in the centre, rounded beneath; aperture elliptical, slightly modified by the last whorl; inner lip planed; outer lip thin; operculum horny, subspiral. Found in brackish water; one species may be procured abundantly on the muddy shores of the Thames, in Kent. There are also species from Calcutta, China, Tahiti, and Australia. Without comparing the animals, it is difficult to distinguish this genus from some species of Littorina. Fig. 363. A. Grayana.

ASTACOLUS. Montf. A genus of microscopic Foraminifera. CRISTELLARIA Crepidula, Lam.

ASTARTE J. Sowerby. (Name of a Sidonian Goddess, Ashtaroth in Scripture.) Fam. Nymphacea, Lam. Genus Crassina, Lam.--Descr. Suborbicular, equivalve, inequilateral, thick, compressed; hinge with two solid diverging teeth in the right valve, one tooth and a slight posterior elevation in the left; muscular impressions, two in each valve, uniform, united by a simple palleal impression; ligament external.--Obs. This genus differs from Venus, Cytheræa, &c. in not having a posterior sinus in the impression of the mantle. The hinge also differs in having but two cardinal teeth. Astarte differs from Crassatella in having no internal cartilage in the hinge. Some of the species are British, others are from America, and one from Sicily. The fossils occur in Crag, Lower Oolite, &c. Fig. 110. A. Danmoniensis.

ASTROLEPAS. Klein. CORONULA Testudinaria, Auct. CHELONOBIA, Leach. Fig. 15.

ATLANTA. Lesueur. Fam. Pteropoda, Lam. and Bl.--Descr. Spiral, convolute, transparent, fragile, compressed, with a broad, fimbriated, dorsal keel, and a narrow aperture. This shell, which is called "corne d'ammon vivant," is found in the Atlantic. The small Pteropod, figured in Sowerby's Genera as Limacina, belongs to this genus. Atlanta Helicialis, fig. 220.