A Conchological Manual, George Brettingham Sowerby [little readers .TXT] 📗

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   the margin, and is consequently said to be out of date.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,

 

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

 

BYSSO-ARCA. Valves gaping. Fig. 132.

 

CUCULLÆA. Distant teeth oblique; posterior muscular impression

       prominent. Fig. 133.

 

PECTUNCULUS. Hinge curved. Fig. 134.

 

NUCULA. The same, with a pit in the centre of the hinge,

       including Myopara and Crenella. Figs. 135 to 137.

 

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