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

the outer lip. Fig. 379, 389, P. marmorata; 381, P.

   Strombiformis, (Clavatula, Sw.)

 

   PLEUROTOMARIA. Defr. _Fam._ Turbinacea, Lam.--_Descr._ Turbinated,

   spiral; aperture sub-quadrate, with rounded angles; outer lip with a

   deep slit near its union with the spire.--_Obs._ This genus, which is

   only known in a fossil state, abounds in inferior Oolite, Oxford clay,

   and casts are found in a limestone bed in Norway. The Scissurellæ

   differ in being very minute shells, and are not so trochiform as the

   species of Pleurotomaria, P. reticulata, fig. 341.

 

   PLICACEA. Lam. A family of the order Trachelipoda, Lam. containing the

   following genera:

 

PYRAMIDELLA. Pyramidal, with numerous whorls. Fig. 342.

 

TORNATELLA. Cylindrical, with few whorls. Fig. 343, 344.

 

RINGICULA. Margin reflected. Fig. 540, 541.

 

   PLICADOMUS. Sw. A sub-genus of Pupa, thus described: "spire moderate,

   regular and thick, but gradually conic; the tip obtuse; aperture

   perpendicular; inner lip wanting; outer lip semicircular; the margin

   dilated and reflected. P. sulcata, Chem. 135, f. 1231, 1232." Sw. p.

   332.

 

   PLICATED. (_Plicatus_, folded.) Applied to spiral plaits on the

   columella of some shells. _Ex._ Voluta, fig. 433. Also to the angular

   bendings in the margins of some bivalve shells. _Ex._ Dendostrea, fig.

   181.

 

   PLICATULA. Lam. (_Plicatus_, folded.) _Fam._ Pectenides, Lam.

   Sub-ostracea, Bl.--_Descr._ Irregular, sub-equivalve, sub-equilateral,

   attached by a small part of the surface of one valve, strongly

   plicated; umbones separated by a small, external ligamentary area;

   hinge with two cardinal teeth in each valve, two approximate in one

   valve, received between two distant in the other; cartilage placed

   between the cardinal teeth; muscular impressions one in each

   valve.--_Obs._ The cardinal teeth resembling those of Spondylus,

   distinguish this genus from others of the Lamarckian family Pectenides.

   Very few species are yet known, they are brought from the East and West

   Indies and the Philippine Islands. Fossil species are found in several

   of the supra-cretaceous beds. Fig. 178, P. gibbosa.

 

   PNEUMOBRANCHIA. Lam. The second section of the order Gasteropoda, Lam.

   containing the family Limacinea, fig. 256 to 263.

 

   PODOPSIS. Lam. This genus appears to have been described from specimens

   of a species of Spondylus, with the triangular disc broken out, so as

   to present a similarly shaped foramen, which was supposed to afford a

   passage for a large byssus.

 

   POLINICES. Montf. A genus composed of NATICA Mammilla, and other

   similar species, with mammillated spires, and the umbilicus filled with

   enamel. Fig. 327.

 

   POLLIA. Gray. TRITONIDEA, Sw. The name given by Gray was pre-occupied

   by a genus of Lepidopterous Insects.

 

   POLLICIPES. Leach. (_Pollex_, a thumb's breadth; _pes_, a foot.)

   _Order._ Pedunculated Cirripedes, Lam.--_Descr._ Conical, compressed,

   consisting of numerous valves, mostly in pairs, three or four pairs

   forming the principal part of the shell, and surrounded at the base by

   two or three rows of smaller valves, supported on a scaly, short

   pedicle.--_Obs._ This description will be found to exclude Scalpellum,

   and Smilium, the valves of which are more equal. The P. Mitellus, Auct.

   (fig. 37*), has been separated as a genus under the name of Mitellus by

   some authors, and it is certainly very different from P. polymerus,

   fig. 37, and P. cornucopia.

 

   POLLONTES. Montf. MILIOLA, Bl. A genus of microscopic Foraminifera.

 

   POLYBRANCHIATA. Bl. ([Greek: Polus], _polus_, many; _branchiæ_, gills.)

   The fifth family of the order Lamellibranchiata, Bl. containing the

 genera Arca, Pectunculus and Nucula, which have a series of small teeth

   on the hinge.

 

   POLYDONTES. Montf. ([Greek: Polus], _polus_, many; [Greek: odos],

   _odos_, tooth.) A species of Helix, shaped like CAROCOLLA, and having a

   number of teeth in the aperture.

 

   POLYGONAL. Many-sided.

 

   POLYGONUM. Schum. ([Greek: Polus], _polus_, many; [Greek: gônia],

   _gonia_, an angle.) A genus composed of species of TURBINELLA, Auct.

   which have large continuous costæ, so as to present the appearance of

   many-sided shells. T. polygonus, fig. 383. This generic name may be

   used to include all those species of Turbinella, Auct. which have very

   small folds on the columella.

 

   POLYGYRA. Say. A genus of Heliciform shells, characterized by the large

   number of close set whorls, constituting the spire. _Ex._ P.

   Septemvolvus, fig. 275, 276.

 

   POLYLEPAS. Bl. ([Greek: Polus], _polus_, many; [Greek: lepas], _lepas_,

   rock.) SCALPELLUM, Auct.

 

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

 

   POLYPHEMUS. Montf. A genus composed of species of ACHATINA, Auct. which

   have elongated apertures, short spires, and an undulation in the outer

   lip. P. Glans, fig. 288.

 

   POLYPLAXIPHORA. Bl. The second class of the sub-type Malentozoa, Bl.

   containing the genus Chiton.

 

   POLYSTOMELLA. Lam. A genus of microscopic Foraminifera.

 

   POLYTHALAMACEA. Bl. ([Greek: Polus], _polus_, many; [Greek: THalamos],

   _thalamos_, chambers.) The third order of Cephalophora, Bl. the shells

   of which are described as straight, more or less symmetrically

   convolute, divided into several chambers. The septa are sometimes, but

   not always, pierced by one or more siphons. This order is divided into

   the families, Orthocerata, Lituacea, Cristacea, Ammonacea, Nautilacea,

   Turbinacea, Turriculacea, all of which contain genera of chambered

   shells. De Blainville arranges these families according to the degree

   in which the spires revolve. The first being straight, as the

   Orthocerata, and the last being so closely coiled up, that the last

   whorl covers the rest, as in the Nautilacea.

 

   POLYTHALAMIA. Lam. The first division of the order Cephalopoda, Lam.

   containing the following families of chambered shells, viz.

   Orthocerata, Lituacea, Cristacea, Sphærulacea, Radiolata, Nautilacea,

   Ammonacea. Fig. 463 to 484.

 

   POLYTROPA. Sw. A genus of "Scolyminæ," Sw. thus described:

   "Bucciniform; but the base narrow, and ending in a straight and

   contracted, but rather short, channel; spire longer, or as long as the

   aperture; exterior folliculated, or tuberculated; inner lip flattened,

   as in _Purpura_; basal notch small, oblique; no internal channel;

   crispata. En. Méth. 419, f. 2. Chem. 187, f. 1802. Capilla, Pennant,

72, f. 89, imbricata. Mart. 122. f. 1124. ? rugosa. Chem. f.

   1473-4." Sw. p. 305.

 

   POLYXENES. Montf. A genus of microscopic Foraminifera.

 

   POMATIA. Gesner. (Gray, Syn. B. M. p. 133.) A genus of the family of

   "Cyclostomidæ," described as having "an elongated shell with reflexed

   lips, and a horny spiral operculum." Also a sub-genus of Snails,

   containing HELIX pomatia, Auct. (Gray's Turton, p. 135.)

 

   PORNUS. Humph. AMPULLARIA, Lam.

 

   PORCELLANA. Adanson. MARGINELLA, Auct.

 

   PORODRAGUS. Montf. A genus composed of species of Belemnites, placed by

   De Blainville in the section characterized as swelled near the apex,

   and straightened towards the base.

 

   POSIDONIA. Brong. A genus formed on the cast of a bivalve shell, common

   on schists from Dillemberg.

 

   POSTERIOR. (_After_, _behind_.) The posterior or hinder part of a

   bivalve shell, is that in which the siphonal tube of the animal is

   placed. It is known in the shell, by the direction of the curve in the

   umbones, which is from the posterior towards the anterior; also by the

   ligament, which is always placed on the posterior part of the hinge,

   when it exists only on one side of the umbones; and by the sinus (when

   there is one) in the palleal impression, which is always near the

   posterior muscular impression. In some shells, however, it is very

   difficult for a learner to trace these marks; such bivalves, for

   instance, as have the ligament spread out on both sides of the umbones;

   such as are nearly symmetrical, and have the umbones consequently

   straight, and a single muscular impression near the centre of the

   valve. The Brachiopodous bivalves have a different position, with

   relation to the animal, from the other bivalves, so that the hinge line

   is the posterior extremity, and the part where the valves open, is the

   anterior. The posterior extremity of the aperture of a spiral univalve

   shell, is that nearest to the spire. In patelliform shells the anterior

   and posterior extremities are distinguished by the muscular impression,

   which is annular, enclosing a central disc in the inner surface of the

   shell, excepting where it is interrupted by the place where the head of

   the animal lies, which of course is anterior. The posterior is marked

   _p._ in fig. 119, and 387. See ANTERIOR.

 

   POSTERO-BASAL MARGIN of a bivalve shell is the posterior side of the

   margin opposite the hinge.

 

   POSTERO-DORSAL MARGIN is the posterior side of the hinge.

 

   POTAMIS or POTAMIDES. Brong. A genus of fresh-water shells resembling

   Cerithium in the characters of the aperture, but which may be known

   from that genus by the thick, horny epidermis with which they are

   coated. P. muricata, fig. 377. (Cerithium, Sow.) We think that these

   shells should be placed near MELANIA.

 

   POTAMOMYA. A genus of shells resembling Corbula, in every respect

   except that of being inhabitants of fresh-water. Fig. 498, 499,

   represents one of these fresh-water Corbulæ.

 

   POTAMOPHILA. Sow. ([Greek: Potamis], _potamis_, river; [Greek:

   philios], _philios_, choice.) "Conques fluviatiles," Lam.--_Descr._

   Thick, equivalve, inequilateral, trigonal, covered with a greenish

   brown, smooth, horny epidermis; hinge thickened, broad, with one

   central, notched cardinal tooth in one valve, and two in the other,

   with indistinct lateral teeth; ligament large, supported on prominent

   fulcra; muscular impressions two in each valve, sub-orbicular.--_Obs._

   The name given to this shell refers to its place of abode, being found

   in rivers. It is the Venus sub-viridis of some authors, although being

   a fresh-water shell, and having an incrassated hinge, and a smooth,

   thick epidermis, it is most distinct from that genus. It is described

   by Bowdich under the name Megadesma, on account of its large ligament,

   and by Lamarck under that of Galathæa, a name previously used by him

   for a genus of Crustacea. P. radiata, fig. 115. Megadesma appears to be

   the preferable name, since it has the right of priority over

   Potamophila. It is found in Africa.

 

   PRIAMUS. A genus composed of ACHATINA Priamus, Lam. BUCCINUM

   Stercus--Pulicum, Chemn. Conch. 9. t. 120. f. 1026-7. This shell is

   ascertained to belong to a marine mollusc, having a horny operculum,

   and therefore is justly considered to form a distinct genus, allied to

   the Buccina and Struthiolariæ. Fig. 545.

 

   PRISODON. Schum. HYRIA, &c. Auct. Fig. 144.

 

   PRODUCED. (_Productus_, prominent.) A term applied to the spire of

   univalve shells, or to any other prominent portion.

 

   PRODUCTA. Sow. (_Productus_, produced.) _Fam._ Brachiopoda,

   Lam.--_Descr._ Equilateral, inequivalve, thick, striated; one valve

   generally convex, with the margin inflected, produced; the other valve

   flat, or slightly convex, with the margin reflected; hinge rectilinear,

   transverse.--_Obs._ The peculiarity of this genus, from which it

   derives its name, is the manner in which the anterior margins of the

   valves are drawn out and overwrap each other. The genus is only known

   in a fossil state. Species occur in Mountain Limestone, and Transition

   Limestone of older date. P. depressa, fig. 206.

 

   PROSERPINA. Gray? Fig. 274, represents a small shell belonging to the

   Helix tribe, to which it is believed, Mr. Gray has applied the name

   Proserpina nitida. We do not know how the genus is defined.

 

   PROTO. Defr. A fossil shell resembling TURRITELLA, but having a spiral

   band reaching to the centre of each valve. P. terebralis, Bl.

 

   PSAMMOBIA. Lam. _Fam._ Nymphacea, Lam.--_Descr._ Transverse, oblong,

   slightly gaping at both ends; hinge with two cardinal teeth in one

   valve, one in the other; ligament supported upon a prominent fulcrum;

   muscular impressions two in each valve, sub-orbicular, distant; palleal

   impression with a large sinus; epidermis thin.--_Obs._ The genus thus

   described includes PSAMMOTÆA of Lamarck, which, according to him, only

   differs in the number of teeth, and which he says are but "Psammobies

   dégenerées." The difference appears to be accidental. This genus

   differs from Tellina in not having a posterior fold in the margin. Fig.

The species are found in temperate and tropical climates.

 

   PSAMMOCOLA. Bl. ([Greek: psammos], _psammos_, sand; _cola_, an

   inhabitant.) A name given by De Blainville to shells of the genus

   PSAMMOBIA, including PSAMMOTÆA of Lamarck.

 

   PSAMMOTÆA. See Lam. PSAMMOBIA.

 

   PSEUDOLIVA. Sw. A genus of "Eburninæ," Sw. thus described: "Shell

   thick, oval, oliviform, ventricose; spire very short, acute; base with

   two parallel grooves, one of which forms a notch at the base of the

   outer lip; suture slightly channelled; inner lip very thick, and

   turning inwards; aperture with an internal canal. Connects the

   TURBINELLIDÆ with the VOLUTIDÆ. P. plumbea, Chem. 188. f. 1806, 1807."

   Sw. p. 306.

 

   PSILOSTOMATA. Bl. The third family of Aporobranchiata, Bl. containing

   no genera of shells.

 

   PTEROCERAS. Auct. ([Greek: Pteron], _pteron_, a