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Read Ebook: A Conchological Manual by Sowerby G B George Brettingham
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NON-SYMMETRICAL UNIVALVES.
The septa of Limpets assume a variety of forms, the principal of which will be seen in the accompanying engravings.
SPIRAL NON-SYMMETRICAL UNIVALVES.
The entire edge of the aperture described generally, is named the Peritr?me, but this term can only be conveniently applied in cases where, in some at least of its characters, it is the same all round, so that one descriptive term is applicable to the whole. As, however, this is of rare occurrence, it is found convenient in descriptions to separate the rim from the outer lip. In a great number of instances, this is done naturally, by a canal, or notch at the anterior or lower extremity, and by the posterior union of that part which overlays the body whorl with the other portion. At these two points the outer and inner lips separate from each other: we therefore describe the
COLUMELLAR LIPS.
OPERCULUM.
The size of the operculum is distinguished by comparison with the rest of the shell; thus, those of Strombus, Cassis, &c. are small; while those of Cyclostoma and others are large, filling up the cavity at its outer edge.
BIVALVE SHELLS.
GENERAL CHARACTER OF BIVALVES.
A great number of Bivalves are extremely regular in their form. These are generally locomotive, and consequently free from those obstructions in growth occurring to stationary shells, which being confined in a particular position, or to a particular spot, modify their shape according to the substance with which they come in contact, and thus become irregular. This is generally the case with shells which are attached to submarine substances, such as Spondyli, Oysters, &c.; and the degree of irregularity will depend upon the extent of surface involved in the attachment. In the case of fixed shells, the attached valve is usually termed the under valve, and the other which moves freely upon the hinge, is termed the upper valve.
MULTIVALVE SHELLS.
In the foregoing explanations we have omitted many of those general terms which, relating to external characters, are applicable to shells in almost every division of the system. It may be as well, however, to enumerate a few of them in this place, although they are explained under their respective letters in the alphabetical part of the work.
GENERAL ARRANGEMENT
ACCORDING TO LAMARCK.
In Lamarck's "Histoire Naturelle des Animaux sans Vertebres," he divides the invertebrata into classes, the 9th, 10th, and 11th of which include animals possessed of shells properly so called. These are the ANNELIDES, the CIRRIPEDES, the CONCHIFERA, and the MOLLUSCA.
Class CIRRIPEDES.
Conchological writers are not agreed as to the propriety of allowing the above to enter into the present science.
Class CONCHIFERA.
The shell of a conchiferous animal is always bivalve, composed of two pieces placed opposite to each other, joined at the dorsal margins by an elastic hinge. All true bivalve shells belong to animals of this class; and the correspondence between the shell and the animal is so true that on examining an empty bivalve shell we can not only determine that its inhabitant belonged to this class, but also decide on the particular order and family in which it should be placed, without seeing the soft parts.
The first general division of Conchifera is that which results from observing the muscular impressions, or marks made on the inner surface of the valve by the insertion of the adductor muscles. All Conchifera are divided into two orders, as follows:
Having two adductor muscles, and consequently two impressions in each valve. They are separated into the following families:
Having one adductor muscle, and therefore only one impression in each valve. They are separated into the following families:--
MOLLUSCA.
This order, containing hyaline, symmetrical, non-spiral shells, as above described, is not divided into families, but contains the following genera, Hyalaea, Cleodora, Limacina, Cymbulia; the first of which, although composed of a single piece, resembles a bivalve so nearly, that Linnaeus actually placed it in his genus Anomia.
All the remaining spiral non-symmetrical shells are arranged in this order, which is divided into the following families:--
The only shells included in this order belong to the genera Argonauta , placed here by Lamarck, and Bellerophon , a fossil genus subsequently added.
The singular and beautiful transparent shell contained in this order, under the generic name Carinaria, forms a covering to a small portion of an animal, equally remarkable and equally distinct from those of all other orders.
The above arrangement, although far from perfect, and requiring numerous modifications, is perhaps liable to as few objections as any other yet proposed, and will certainly be more easily understood by those who have not the opportunity of studying the soft parts of the animal.
CONCHOLOGICAL MANUAL.
ABIDA. Leach. A genus founded on a species of PUPA, which has the peristome slightly reflected, and numerous plaits in the aperture. Pupa Juniperi, Pupa secale, Draparnaud. Great Britain; also Central and Southern Europe.
ACAMAS. Montfort. BELEMNITES multiforatus, Blainville. A species described as being perforated at the apex, by a stellated perforation. No species of Belemnite at present known agreeing with the description; it is supposed to have been taken from a broken specimen.
ACANTHOCHETES. A name given to a species of Chiton having bunches of bristles at the sides of the valves.
ACARDO. Commer?on. Described from a pair of bony plates, taken from the vertebrae of the Whale, and mistaken for a bivalve shell, destitute of a hinge.
ACCESSARY VALVES, are the smaller or less important testaceous plates, found on the hinge or dorsal margins of the true valves of some shells. Example, the small plates on the hinge of Pholas, fig. 55, a. The Pholades were placed by Linnaeus and Brugui?re among multivalve shells.
ACEPHALOPHORA. Blainville. The third class of the type Malacozoaria, Bl. including all bivalve shells, the animals of which have no distinct head. This class corresponds with the Conchifera of Lamarck, and is divided into the orders Palliobranchiata, Rudistes, Lamellibranchiata, and Heterobranchiata, the last of which contains no genera of testaceous Mollusca.
ACHATINELLA. SOW. A small group of shells, differing from Achatina in having the inner edge of the outer lip thickened, and a slight groove near the suture of the spire. Fig. 287. Sandwich Islands.
ACHELOIS. Montf. CONILITES Achelois. Knorr. Supp. T. 4, fig. 1.
ACICULA. Nilson. ACHATINA Acicula, Auct. CIONELLA, Jeffreys.
ACIONA. Leach. A genus described by De Blainville as consisting of those species of Scalaria, the whorls of which do not touch each other. If this account be correct, the genus proposed by Leach will include the typical species of Scalaria, such as S. pretiosa.
ACME. Hartmann. A genus formed of TURBO fuscus, Walker. AURICULA lineata, Drap. thus described--"Shell sub-cylindrical, with a blunt tip; mouth ovate, simple, thin, slightly reflected over the pillar, forming a slight perforation." The animal is said to resemble a Cyclostoma, but has no operculum. Auricula lineata, Drap. Hist. 57, t. 3, fig. 20, 21. Southern Europe.
ACTEON. Montf. TORNATELLA, Lam.
ACULEATED. Beset with sharp spines, as the margin of Chiton aculeatus, fig. 227.
ACUMINATED. Terminating in a point, as the apex of Melania subulata, fig. 313.
ACUS. Humphrey. TEREBRA of Lamarck.
ACUTE. Sharp, pointed, or sharp-edged.
ADDUCTOR MUSCLE. That which draws the two valves of a shell together, and leaves a mark on the inner surface of each, called the MUSCULAR IMPRESSION.
ADELOSINA. D'Orb. A genus of microscopic Foraminifera.
AGANIDES. Montf. ORBULITES, Lam.
AGATHIRSES. Montf. SILIQUARIA, Auct.
AKERA. Bl. The fourth family of the order Monopleurobranchiata, Bl. containing the genera Bulla, Bullaea and Bellerophon, which, excepting the last, constitutes the family Bullaeana, Lam.
ALATAE. Lam. A family of the order Trachelipoda, Lam. containing the following genera which may be thus distinguished.
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