Part 14

ANOMIA. Fam. Ostracea, Lam. and Bl.--Descr. Irregular, inequivalve, sub-equilateral, foliaceous, pearly within; adhering to marine substances by means of a bony appendage, which passes through a large circular opening in the lower valve; muscular impression divided into three irregular portions; hinge destitute of teeth with a short cartilage.--Obs. The Linnæan genus included not only the shells to which the description above given would apply, but also many other genera, such as Crania, Orbicula, Terebratula, &c. which belong to the Brachiopoda, and are perfectly distinct. The Anomiæ are found in Europe, N. America, Moluccas, Philippine Islands, &c. Fig. 186, in the plates, is a somewhat reduced representation of a full grown specimen of A. Ephippium. Fig. 187, the hinge of the under valve, with the bony process. Fig. 188, the hinge showing the opening through which it passes.

ANOSTOMA. See ANASTOMA.

ANSATES. Klein. A genus formed of those species of Patella which have a produced, recurved beak. Helcion, Montf. Ex. Patella pellucida, fig. 230.

ANSULUS or ANSYLUS. Mr. Gray conjectures that the name of the genus Ancylus, should be so written.

ANTENOR. Montf. A genus of microscopic Foraminifera.

ANTERIOR. In Bivalves is the side on which the head, or part analogous to the head of the animal lies; it is known in the shell by the umbones, which if turned at all, are turned towards that part. If there be a sinus in the impression of the mantle, it is always on the posterior part of the shell. If the ligament be placed only on one side of the umbones, it is only on the posterior side. The anterior of a spiral univalve is that part of the outer lip which is at the greatest distance from the apex. Of a symmetrical conical univalve such as Patella, it is that part where the head of the animal lies, indicated by the interruption of the muscular impression. Of cirripedes, that part where the ciliæ protrude are anterior; of Brachiopoda, that part which is farthest from the umbones and which corresponds with the ventral margin in other Bivalves. The anterior of symmetrical, convolute univalves, is the outer or dorsal part of the aperture, or that part which is farthest from the spire. Lamarck and other Conchological writers have occasioned much confusion by their errors on this subject; describing the same part of a shell at one time anterior, at another posterior; but generally the reverse of the above arrangement, which is founded upon the natural position of the animal, and generally adopted. The anterior will be indicated by the letter a, in figs. 119, 421, 229, 34, 202.

ANTIGONA. Schum. A genus composed of VENUS cancellata, Lam. (fig. 119.) and similar species.

ANTIQUATED. This word, signifying out of date, is occasionally used to express that species of composition which constantly occurs in shells, by each fresh deposit or layer of calcareous matter, forming a new margin, which being replaced by its successor, is no longer used as the margin, and is consequently said to be out of date.

APEX. This term does not apply to the natural position of a shell, but is used in a mathematical sense, to indicate the nucleus or first formed part; which may be considered as the point of the spiral cone. From this point, the shell enlarging rapidly or slowly as it descends, takes a spiral, arched, straight, oblique, convolute, or irregularly spiral course. The apex will be indicated by the letter a, in fig. 282 and 466.

APERTURE or MOUTH. The entrance to the spiral cavity of univalve shells. The parts of the aperture are separately described, as follows: The inner lip or labium is that part which lies over the preceding whorl of the shell. It terminates anteriorly, or towards the lower part in what is termed the columella, so called because it forms a kind of axis on which the volutions turn. The outer lip, sometimes called the labrum, is on the opposite side, or the farthest from the axis. If the edges of the inner and outer lips unite all round, they are described as composing the peritrême. In fig. 318, the aperture is marked by the letter a.

APHRODITA. Lea. (from [Greek: Aphroditê], Greek name of Venus.) A genus composed of CARDIUM Groenlandicum, Auct. fig. 123*, and other similar species of Cardium, the teeth of which are either wholly wanting, or very indistinct. Northern Ocean.

APICIAL. Belonging to the apex. The apicial extremity of the aperture of a univalve shell, is that which is nearest to the apex of the spire.

APICULUM. Humph. TROCHUS, Lam.

APLEUROTIS. Rafinesque. A genus unfigured and imperfectly described as differing in some respects from Terebratula and other Brachiopodæ.

APLEXUS. Fleming. A genus composed of PHYSA Hypnorum, Drap. &c. and described as having the inner lip simple, and not spread over the body whorl.

APLODON. Rafinesque. A genus proposed to be established at the expense of the genus HELIX, but upon what grounds does not appear from the imperfect description which is unaccompanied by a figure.

APLUSTRE. Schum. A genus formed for the reception of those species of BULLA which have the spire uncovered. Ex. Bulla Aplustre, (aplustre, a flag.) Auct. fig. 289.

APLYSIA. Linn. (a, without; [Greek: Pluô], to wash.) Fam. Laplysiens, Lam. Aplysiana, Bl.--Descr. Horny, transparent, clypeiform, or shield-shaped, placed horizontally on the back of the animal, with its convex side uppermost; apex slightly incurved.--Obs. The animal producing this shell has derived its name from the purplish liquor which it exudes, when disturbed. In contour, it has been fancied to present a certain likeness to a hare crouching, and on this account was called Lepus marinus, or sea hare, by the ancients. The shell bears a strong resemblance to Dolabella, which, however, is much thicker, and more testaceous. The species are found in the Mediterranean, European, and West Indian Seas. A. Petersoni, fig. 254.

APLYSIACEA. Bl. The second family of the order Monopleurobranchiata, Bl. The animals composing this family are either destitute of shells, or are provided with internal ones, which are flat, open, oblique, with the apex or nucleus slightly incurved, not distinctly spiral. This family contains the genera, Aplysia and Dolabella. The first sub-spiral, with the apex terminal; shell thin, horny. Fig. 254. The second the same, but thick and shelly. Fig. 255.

APOLLON. Montf. RANELLA Ranina, Auct. Placed by De Blainville in that division of Ranella, which is characterized as being umbilicated. Fig. 393.

APOROBRANCHIATA. Bl. The first order of the second section of Paracephalophora Monoica, Bl. The Thecosmata is the only family of this order containing any approach to shells, these are Hyalæa and Cymbulia.

APORRHAIS. Petiver. A genus formed of ROSTELLARIA Pes-pelicani, Auct. (fig. 404) and similar species. Although the shell presents no characters to distinguish it generically from Rostellaria, those who have examined the soft parts are convinced that it is distinct. Of the three species now known and figured in part I. of Thesaurus Conchyliorum, by the Author, one is common on our own coast, and in the Mediterranean; also North America. See ROSTELLARIA.

AQUATIC. A term applied by some authors to those species of Molluscous animals, which inhabit fresh water, either in rivers, or salt water standing pools, as distinguished from the marine or Mollusca. See Fresh-water.

AQUILLUS. Montf. TRITON Lampas, Cutaceus, &c. Auct. Placed by De Blainville in the division of the genus Triton, which is described as having a short spire, being covered with tubercles and umbilicated. Triton Cutaceus, fig. 399.

ARCA. Auct. (Anglicè, a boat.) Fam. Arcacea, Lam.--Descr. Obliquely transverse, subquadrate, equivalve, or nearly so, inequilateral, thick, ventricose, longitudinally ribbed, dentated near the inner margins; hinge rectilinear, forming a flat, external area, upon which the ligament is spread in cross rows, and having a series of small, regular teeth, extending on both sides of the umbones in each valve; muscular impressions distant.--Obs. The shells composing this genus are easily distinguished from those of all other bivalve shells, by the straight, linear row of small, notched teeth, and by the area between the umbones. The genus Cucullæa makes the nearest approach to it in this respect, but it may easily be known from it by the outermost teeth on each side of the row being oblique, and lengthened out; and also by the prominent edge of the muscular impression. These shells are found recent, in various marine localities; fossil, in the tertiary deposits. The Arca Noæ, formerly regarded as the type of this genus, has, with several other species, been separated from it under the name of Bysso-arca, by Swainson, on account of an hiatus in the ventral margin, to admit the passage of a byssus; this is not found in the true Arcæ. The true Arcæ are mostly tropical. Arca Antiquata, fig. 131. Bysso-arca Noæ, 132.

ARCACEA. Lam. A family of the order Conchifera Dimyaria, characterized by a series of teeth placed on the hinge in a line. The genera may be distinguished as follows,

1. ARCA. Hinge straight; valves close. Fig. 131.

2. BYSSO-ARCA. Valves gaping. Fig. 132.