Part 20

PHOS. Montf. _Fam._ Purpurifera? Lam.--_Descr._ Turrited, thick, cancellated, varicose; spire pointed, generally longer than the aperture; aperture rounded or oval; outer lip having internal ridges, with a sinus near the anterior termination; columella with an oblique fold; canal short, forming externally a raised varix.--_Obs._ The raised external surface of the canal, brings this genus near to Buccinum, while, in general appearance, most of the species more nearly resemble Murex. They have, however, no true varices on the whorls, but merely raised bars. Fig. 416, P. senticosus.

PHYLLIDIANA. Lam. A family belonging to the first section of the order Gasteropoda, Lam. The genera belonging to this family may be distinguished as follows:

1. CHITON. Composed of eight valves; valves contingent. Fig. 227.

2. CHITONELLUS. The same, with the valves distant. Fig. 228.

3. PATELLA. Conical, symmetrical. Fig. 229, 230.

4. PATELLOIDA. Differing from Patella in the animal. Fig. 231.

5. SIPHONARIA. With a siphon on one side. Fig. 231*.

6. SCUTELLA. Siphon close to the side of the head. Fig. 510, 511.

PHYLLONOTUS. Sw. A sub-genus of Murex, thus described: "Canal moderate; varices foliated, laciniated, compressed, or resembling leaves; inflatus. Mart. 102. fig. 980, eurystoma. Zool. Ill. ii. 100. imperialis. Ib. pl. 109." Sw. p. 296.

PHYSA. Drap. A genus formed for reversed species of Limnæa, Auct. Fig. 310, P. castanea.

PHYSETER. Humph. SOLARIUM, Lam.

PILEOLUS. Cookson. (_A little cap._) _Fam._ Neritacea, Lam.--_Descr._ Patelliform, with the apex sub-central, straight. In the lower disc, or under surface, the centre of which is rather raised or cushion-shaped, is placed the lateral, narrow, semilunar aperture, with the outer lip marginated and the inner lip crenulated.--_Obs._ This interesting genus is known only in a fossil state. Two species are found in the upper layer of Oolite, above the Bradford clay. The spire, although internal, connects this genus in some degree with Neritina. Still there is no danger of confounding them. Fig. 332, P. plicatus.

PILEOPSIS. Lam. CAPULUS, Montf.

PILLAR. The usual English name for the column which forms the axis of spiral shells, around which the whorls revolve. See COLUMELLA.

PINNA. Auct. (_The fin of a fish._) _Fam._ Mytilacea, Lam.--_Descr._ Equivalve, inequilateral, oblique, wedge-shaped, thin, horny; umbones terminal; hinge rectilinear, without teeth; anterior margin sinuated, to admit the passage of a byssus; posterior margin truncated, gaping; muscular impressions two in each valve; posterior large, sub-central; anterior small, terminal, sometimes double.--_Obs._ The beautiful large shells of which this genus is composed, are possessed of a large, flowing, silky byssus, of which gloves and hose have been manufactured. They have received their name from their resemblance to the pectoral fins of some fishes. Some species attain very large dimensions, and measure two feet in length. A very improbable story is told with regard to animals of this genus, namely that a certain small species of crab is in the habit of taking refuge from its enemies in the shell of the Pinna, into which it is received with great hospitality and kindness by the "_blind slug_," which inhabits it. In return for which kindness, he occasionally goes abroad to procure food for both. On his return he knocks at the shell, which is opened to receive him, and they share the supplies together in convivial security! Some species are smooth, although the greater number are imbricated or crisped outside. P. saccata, fig. 162.

PINNATED. (From _Pinna_, a fin.) When a part of a shell is spread out and smooth, as in Rostellaria columbaria, fig. 403, it is said to be _alated_, or winged, but when the part which is spread is radiated or ribbed, like the fin of a fish, it is _pinnated_, as in Murex pinnatus, and Murex tripterus. (Conch. Illustr.)

PIRENA. Lam. A genus of fresh-water shells, rejected by De Ferussac and other authors, who place Lamarck's two first species with Melanopsis, and his two last with Melania. Fig. 316, P. terebralis.

PISIDIUM. Leach. A genus of river shells separated from Cyclas principally on account of a difference in the animal. The species of Pisidium, however, are less equilateral than the Cyclades, and the posterior or ligamentary side of the latter is the longer, while that of the former is the shorter. Fig. 112.

PISIFORM. (_Pisum_, a pea; _forma_, shape.) Shaped like a pea or small globular body.

PISUM. Megerle. (_A pea._) PISIDIUM, Leach.

PITHOHELIX. Sw. A sub-genus of "Geotrochus," Sw. Sw. p. 332.

PITONELLUS. Montf. ROTELLA, Auct.

PLACENTA. Schum. PLACUNA, Auct.

PLACENTULA. Schum. A genus of microscopic Foraminifera.

PLACUNA. Brug. ([Greek: plakous], _placos_, a cake.) _Fam._ Ostracea, Lam. and Bl.--_Descr._ Compressed, thin, equivalve, nearly equilateral, planorbicular, fibrous, foliaceous; hinge flat, with two diverging ribs in one valve, and two corresponding grooves in the other, containing the cartilage; muscular impressions one, large, circular, central, and one or two smaller in each valve.--_Obs._ The two best known species of this well defined genus are the P. Placenta, commonly called the Chinese Window Shell, and the P. Sella, called the Saddle Oyster, from the anterior margin being turned up so as to resemble a saddle. The genus may be known from all others by the diverging costa on the hinge. Placunanomia is the only genus resembling it in this respect, but this is easily distinguished by a perforation through the shell. Fig. 184, P. Placuna. These shells are used in China to glaze windows.

PLACUNANOMIA. (Sw. _Placuna_ and _Anomia_.) _Fam._ Ostracea, Lam. and Bl.--_Descr._ Thin, foliaceous, compressed, sub-equivalve, sub-equilateral, irregular, flat near the umbones, plicated towards the margins, attached by a bony substance passing through a fissure in the lower valve; hinge flat, with two diverging ribs in one valve, corresponding with two diverging grooves, containing the cartilage, in the other; muscular impressions one in each valve, central, sub-orbicular.--_Obs._ The specimens from which Mr. Broderip described this singular genus, were brought by Mr. Cuming from the gulf of Dulce in Costa Rico. Another species is from one of the Philippine Islands. They partake of the characters of several genera, having the hinge of Placuna, and being attached by a process passing through the lower valve, like Anomia. P. Cumingii, fig. 189.

PLAGIOSTOMA. Sow. Min. Con. ([Greek: plagios], _plagios_, oblique; [Greek: stoma], _stoma_, mouth.) _Fam._ Pectenides, Lam. Palliobranchiata, Bl.--_Descr._ Sub-equivalve, inequilateral, oblique, auriculated on each side of the umbones, radiately striated; hinge straight in one valve, with a triangular notch in the other.--_Obs._ This genus, one species of which is spinous, and another smooth, is only known in a fossil state. It is found in the Lias and chalk. Fig. 176, P. spinosum.

PLAIT or FOLD. A term applied to the prominences on the columellar lip of some univalve shells, particularly in the sub-family of Volutidæ. _Ex._ Voluta, fig. 433; Cymba, 434; and Melo, fig. 435.

PLANARIA. Brown. A minute fossil resembling Planorbis in appearance, but differing in being a marine shell, and having a reflected outer lip. P. nitens, fig. 312, from Lea's Contributions to Geology.

PLANAXIS. Lam. (_Plana_, flat; and _axis_.) _Fam._ Turbinacea, Lam. Entomostomata, Bl.--_Descr._ Sub-ovate, pyramidal, solid; spire measuring ½ or 1/3 of the axis, consisting of few whorls; columella contiguous to the axis, flat, truncated, and separated from the outer lip by a short canal; outer lip thickened and denticulated within; operculum horny, thin, with a terminal nucleus.--_Obs._ This is a genus of small marine shells found in the West Indies, &c. Fig. 365, P. sulcata.

PLANE. (_Planus._) Flat, planed, as the columellar lip of Purpura, fig. 414.

PLANORBICULAR, (_Planus_, flat; _orbis_, an orb.) Flat and circular, as Ammonites, fig. 478.

PLANORBIS. Müll. (_Planus_, flat; _orbis_, an orb.) _Fam._ Lymnacea, Lam. and Bl.--_Descr._ Thin, horny, convolute, planorbicular, nearly symmetrical; spire compressed, concave, consisting of numerous gradually increasing whorls, which are visible on both sides; aperture transversely oval, or nearly round; peritreme entire; outer lip thin; inner lip distinct, spread over a part of the body whorl.--_Obs._ This is a genus of shells abounding in all climates in ditches and stagnant pools, not liable to be confounded with any other, excepting the discoidal species of Ampullaria, which may be distinguished by the aperture being broadest in the opposite direction. It is further to be remarked that the discoidal Ampullariæ are dextral shells, and the Planorbes are sinistral or reversed; and although the latter are sometimes so flat and orbicular that it is difficult to know which is the spiral side, it may nevertheless always be ascertained by a careful examination. Fossil species are found in the freshwater strata of the Isle of Wight, and the neighbourhood of Paris. Fig. 311, P. corneus.

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

PLANULACEA. Bl. The second family of Cellulacea, Bl. The microscopic Foraminifera contained in this family are described as very much depressed, not spiral, chambered, cellular, and having the septa indicated by grooves on the external surface of the shell, which increase in length from the apex to the base: some of the small cellular cavities are to be seen on the margins. This family contains the genera Renulina and Peneroplis.

PLANULARIA. Defr. PENEROPLIS, Montf. A genus of microscopic Foraminifera.

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

PLANULITES. Lam. DISCORBITES of the same author. A genus of microscopic Foraminifera.

PLATIRIS. Lea. ([Greek: platus], _platus_, wide; [Greek: iris], _iris_.) A genus including several species of Nayades, referred to IRIDINA, Lam. The genus Platiris is divided into two sub-genera. Iridina, species which have crenulated margins; I. Ovata, I. exotica, Spatha, Lea; those with smooth or very slightly crenulated hinges, S. rubeus, S. Solenoides, Mycetopus, D'Orb. Fig. 151.

PLATYLEPAS. ([Greek: platus], _platus_, wide; [Greek: lepas], _lepas_, rock.) _Order._ Sessile Cirripedes, Lam. _Fam._ Balanidea, Bl.--_Descr._ Conical, depressed, consisting of six valves, each divided internally by an angular plate jutting from the centre (like the buttress of a wall); operculum consisting of four valves in pairs.--_Obs._ This genus differs from Balanus, Coronula, &c. in the internal structure of the valves. De Blainville's description of Chthalamus partly agrees with this. Fig. 19.

PLECTOPHORUS. Fer. ([Greek: plêktron], _plectron_, spur; [Greek: phoreô], _phoreo_, to carry.) A genus consisting of small testaceous appendages fixed on the posterior extremity of a species of slug. P. corninus, fig. 260.

PLEIODON. Conrad. IRIDINA, Lam. _Fam._ Nayades, Lam.

PLEKOCHEILUS. Guild. AURICULA Caprella, Lam. CARYCHIUM undulatum, Leach. (CAPRELLA, Nonnull.) This proposed genus is described as scarcely umbilical, dextral, oval, spiral; with the spire elevated, obtuse; the two last whorls very large, ventricose; aperture entire, elongated; columella with a single plait; the plait concave, inflected. Fig. 522, 523.

PLEUROBRANCHUS. Cuv. ([Greek: Pleura], _pleura_, the side; _Branchiæ_, gills.) _Fam._ Semiphyllidiana, Lam. Subaplysiacea, Bl.--_Descr._ Internal, thin, haliotoid, slightly convex towards the spiral apex; aperture entire.--_Obs._ This is a very light shell, delicately coloured, resembling Aplysia, but differing in the integrity of the margin. Fig. 232, P. membranaceus.

PLEUROCERUS. Rafinesque. A genus very imperfectly described in the "Journal de Physique" as "oval, or pyramidal; aperture oblong; outer lip thin; inner lip truncated at the columella, which is smooth and tortuous, not umbilicated. Operculum horny or membranaceous." De Blainville, in giving this description, remarks that he has neither seen the animal nor the shell of this genus, which he imagines to have been formed from the "Paludine Coupée de M. Say."

PLEURORYNCHUS. Phillips. ([Greek: Pleura], _pleura_, the side; [Greek: runchos], _rynchus_, a beak.) A genus founded upon a very singular species of CARDIUM, distinguished by the short anterior side, and the elongation of the hinge line into auricular processes, which are truncated at the extremities. C. Hibernicum from the Black Rock near Dublin, which is vulgarly called Asses-hoof, and C. elongatum (Sow. Min. Con. vol. I. 82.), form part of this genus.

PLEUROTOMA. Lam. _Fam._ Canalifera, Lam. Siphonostomata, Bl.--_Descr._ Fusiform, thick, in general ribbed or striated transversely; aperture oval, terminating anteriorly in an elongated canal; outer lip thin, with a fissure near its spiral extremity; columella smooth, nearly straight. Found principally in tropical climates.--_Obs._ This genus, which nearly resembles Fusus in other respects, may be known by the notch in the outer lip. The species differ in the length of the canal. Swainson has designated this genus a family, thus divided into genera: Brachytoma, in the description of which he says that the spire and aperture are of equal length, including the species strombiformis: Pleurotoma, in which the channel is so much lengthened, as to be little shorter than the spire: Clavatula, having the long narrow slit of Pleurotoma, but with a very short canal: Clavicantha, having the canal equally short, but the sinus or notch, instead of being linear and long, is short and wide; the surface is rough, and the whorls either coronated with prickles, or with compressed nodules resembling spines: Tomella, which has the spire and canal fusiform, but the spire of very few whorls, and the inner lip considerably thickened within where it joins 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:

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

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

3. 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, pl. 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.