Chapter VIII: Part 8

OTION. Leach. ([Greek: ôtion], a little ear.) _Order._ Pedunculated
Cirripedes, Lam.--_Descr._ Body sub-quadrate, supported on a fleshy
pedicle with a gaping aperture and two posterior auricular tubes;
valves five, separate, two semilunar, placed at the sides of the
aperture, two terminal, very small, one dorsal, minute.--_Obs._ Otion
differs from Cineras in having two cylindrical posterior tubes, and in
the extreme minuteness of three out of five of the valves. Found on
spars floating in the sea, &c. O. Cuvierii, (Lepas aurita, Linn.) Fig.
43, O. Cuvieri.

OTIS. Humph. AURICULA, Lam.

OVATE. (_Ovatus._) Egg-shaped or oval.

OVEOLITHES. Montf. A microscopic shell resembling Bulla.

OVIPAROUS MOLLUSCA. Those which produce their young in eggs. Used in
distinction from the VIVIPAROUS MOLLUSCA, whose young are perfectly
formed before they leave the body of the parent.

OUTER LIP. See LABRUM.

OVULUM. Brug. (_Ovum_, an egg, dim.) _Fam._ Convoluta, Lam.
Angyostomata, Bl.--_Descr._ Ovate or fusiform, smooth, convolute, spire
covered; aperture narrow, with a canal at each extremity; outer lip
crenulated, inflected; inner lip smooth, callous towards the spiral
extremity; dorsal area wide, sometimes indistinctly marked.--_Obs._ The
Ovula were placed by Linnæus in his genus Bulla, from which they are
very remote. They differ from Cypræa in having the inner lip smooth. We
have given representations of their different forms as follows: O.
Ovum, fig. 442. O. verrucosum, (Calpurnus Montf.) fig. 441. O. Volva,
the weaver's shuttle (Radius, Montf.) fig. 442. O. gibbosum, (Ultimus,
Montf.) fig. 443.

OXYSTOMATA. Bl. The fifth family of Asiphonibranchiata, Bl. This family
appears to have been formed for the express purpose of providing a
place in the system for the genus Janthina, which seems to bear so
little analogy with other genera of Mollusca, that conchological
writers have been puzzled to know where to place it.

PACHYLABRA. Sw. PACHYSTOMA, Guild. A sub-genus of Ampullaria, the outer
lip of which is thickened within. _Ex._ Ampullaria globosa.

PACHYMYA. Sow. ([Greek: pachus], _pachus_, thick, and _Mya_.) _Fam._
Cardiacea? Lam.--_Descr._ Obliquely elongated, equivalve, thick,
sub-bilobed, with beaks near the anterior extremity; ligament partly
immersed attached to prominent fulcra.--_Obs._ This singular fossil is
shaped like Modiola, but the shell being extremely thick, and the
ligament attached to a prominent fulcrum, it is difficult to know where
to place it. Fig. 130, Pachymya Gigas.

PACHYSTOMA. Guild. ([Greek: pachus], _pachus_, thick; [Greek: stoma],
_stoma_, mouth.) A genus composed of such species of Ampullaria, Auct.
as have the edge of the aperture thickened and grooved within so as to
form a sort of ledge upon which the operculum rests. Ampullaria globosa
and corrugata are examples of this variation. The name Pachylabra is
given to such species by Swainson, who objects to the above name on
account of its having been previously used to a genus of fishes. Fig.
539.

PACHYTOMA. Sw. A sub-genus of Helicina, thus described, "Aperture
entire; the inner lip very thick; the spiral whorls hardly convex; P.
occidentalis. Zool. J. iii. 15. f. 6-10. viridis, Zool. Journ. i. pl.
6. f. 7." Sw. p. 337.

PACLITES. Montf. A genus composed of species of Belemnites, Auct.
described towards the extremity, with a pore, at the apex, and a
straight lengthened aperture. _Ex._ B. ungulatus, Bl.

PADOLLUS. Montf. A genus composed of species of HALIOTIS, with a
strongly marked spiral groove. _Ex._ H. tricostalis, Lam. Fig. 339.

PAGODELLA. Sw. A sub-genus of Trochus, thus described: "Trochiform;
generally thin, and always not pearlaceous; aperture and pillar
perfectly united and entire; operculum horny. P. major. Mart. 163. f.
1541, 1542. tectum-persicum. Ib. f. 1543, 1544." Sw. p. 351.

PALLEAL IMPRESSION. (_Pallium_, a mantle.) The mark or groove formed in
a bivalve shell by the muscular attachment of the mantle, which, being
always found near the margin of the shell, is sometimes termed the
marginal impression. In bivalves with two muscular impressions it
passes from one to the other. If in passing, it takes a bend inwards
posteriorly, it is said to be sinuated, and that part is called by Mr.
Gray, the Siphonal scar.

PALLIOBRANCHIATA. Bl. The first order of the class Acephalophora. Bl.
The animals of this order are described as more or less compressed,
included between the two valves of a bivalve shell, one inferior, the
other superior, joining at the back and opening in front. The
Palliobranchiata in the system of De Blainville correspond with the
Brachiopoda in the system of Lamarck, and the shells may be known by
their being symmetrical. This order contains in the first section of
symmetrical bivalves, Lingula, Terebratula, Thecidium, Strophomena,
Plagiostoma, Dianchora and Podopsis: in the second section, Orbicula
and Crania.

PALMATED. Flattened like a palm, as the fronds or fringes of some
Murices.

PALMINA. Gray. Differing from OTION in having but one auricle.

PALUDINA. Lam. _Fam._ Peristomata, Lam. Cricostomata, Bl--_Descr._
Varying in form from oval to globose, in some instances oblong, covered
with a greenish horny epidermis; spire acute, composed of rounded
whorls; aperture ovate; peritreme entire, slightly modified by the last
whorl; operculum horny, concentric. Europe, North America, East Indies,
China, &c.--_Obs._ The construction of the operculum distinguishes this
genus of freshwater shells from Valvata and Cyclostoma. The Paludinæ
are viviparous. Fig. 321. P. Achatina.

PALUDOMUS. Sw. A genus of the family of "Melanianæ," Sw. described as
differing from Melania in having the spire shorter than the aperture.
Sw. p. 340.

PANDORA. Brug. _Fam._ Corbulacea, Lam. Pyloridea, Bl.--_Descr._ Thin,
inequivalve, pearly within, rounded anteriorly, rostrated posteriorly;
right valve flat with a cardinal tooth, or short rib, and a slit
containing the cartilage with a narrow plate on the dorsal edge turned
towards the left valve; left valve concave, with a receptacle for the
cardinal tooth of the right valve and the internal cartilage; no
external ligament. Europe, America, Ceylon, &c.--_Obs._ This well known
genus is in no danger of being confounded with any other shell. Fig.
90. P. rostrata.

PANOPÆA. Menard. _Fam._ Solenacea, Lam. Pyloridea, Bl.--_Descr._
Equivalve, inequilateral, oval, gaping at both extremities; hinge with
an acute cardinal tooth in each valve, and a large callosity near the
umbones supporting the ligament; muscular impressions two, distant,
oval; palleal impression with a large sinus. Britain, North America,
Mediterranean, Australia, &c.--_Obs._ This genus resembles Mya in
general appearance, but differs in having an external ligament and a
sharp tooth, instead of the broad spoon-shaped process in the hinge of
the latter genus. Fig. 65. P. Australis.

PAPER SAILOR. A common name given to the Argonauta.

PAPILLARY. (_Papilla_, a teat.) Shaped like a teat. This term is
applied by conchologists when the apex of the spire of an univalve
shell is rounded like a teat and not spiral up to the extreme point; as
the apex of Cymba, fig. 434.

PAPYRACEOUS. (_Papyrus_, a kind of paper made of the flags of the river
Nile in Egypt.) Of a thin, light texture, resembling that of paper. An
example of this is to be seen in the Argonauta, commonly called the
"Paper Sailor," fig. 485, and in the Pholas papyracea, fig. 56.

PAPYRIDEA. Sw. A sub-genus of Cardium, thus described; "Shell
heart-shaped, or transversely oval; inequilateral; the anterior side
almost always gaping; representing the Pholidæ. P. Soleniforme, Wood,
Conch. pl. 56. f. 3.--apertum, Ib. 56. f. 2.--transversum, Sow. Conch.
f. 4.--ringens, Wood, pl. 53. f. 1, 2."

PARACEPHALOPHORA. Bl. The second class of the type Malacozoa, Bl.
divided into the sub-classes: P. dioica, P. monoica, P. hermaphrodita.

PARIES. (_A wall._) The principal part of a multivalve shell, forming a
circular wall round the body of the animal, and composed of one or more
valves which are called the parietal valves.

PARIETAL VALVES. The principal valves of multivalve shells surrounding
the body like a wall; as distinguished from the opercular valves, or
those which compose the operculum.

PARMACELLA. Cuv. (_A little cell._) _Fam._ Limacinea, Lam. and
Bl.--_Descr._ Haliotoid, internal, thin; spire flat, consisting of one
or two rapidly increasing whorls; aperture as large as the whole shell,
with the dorsal margins inflected.--_Obs._ This description applies to
Parmacella of Cuvier. The shell figured in Sowerby's Genera under that
name is Cryptella of Webb. Fig. 257, P. Olivieri. Fig. 258, P.
Palliolum.

PARMOPHORUS. Bl. A genus composed of EMARGINULA elongata, Auct. and
other species of a similarly elongated form. Australian. Fig. 242. P.
elongatus.

PARTULA. Fer. _Fam._ Colimacea, Lam. Auriculacea, Fer.--_Descr._
Conical, smooth; spire equal to the aperture in length, consisting of
few whorls; aperture auriform; outer lip reflected, broad; inner lip
reflected, with a slight prominence on the columella. P. australis,
fig. 302.

PASITHÆA. Lea. A genus formed of some pyramidal shells, described as
resembling Melania, but separated from that genus on account of being
marine fossils. Fig. 317, P. striata.

PATELLA. Auct. (_A dish_ or _platter_.) _Fam._ Phyllidiana, Lam.
Retifera, Bl.--_Descr._ Symmetrical, compresso-conical, nearly regular,
oblong or oval; apex sub-central, inclining towards the anterior
margin; aperture oval, forming the base of the shell; internal surface
smooth; with a muscular impression shaped like a horse-shoe, with the
ends bending forwards, encircling and dividing the space all round,
except where the interruption occurs to receive the head of the animal;
external surface ribbed, grooved, striated or banded radiately. On
rocks and sea-weeds in all climates.--_Obs._ Patelloida differs from
Patella in the construction of the animal; Siphonaria, in the lateral
siphon; and Ancylus, in the oblique twist of the axis, as well as in
the nature of the animal. The Patellæ are marine. Fig. 229, P. Oculus.

PATELLIFORM. (_Patella_, a dish; _forma_, shape.) Shaped like a dish,
or like shells of the genus Patella.

PATELLOIDA. Quoy and Gaimard. LOTTIA, Gray.--_Fam._ Phyllidiana,
Lam.--_Descr._ Patelliform, rather flat; apex obtuse, leaning towards
the posterior margin; muscular impression not symmetrical, but widest
on the right side near the head of the animal; central disc of a
variable brown colour. On rocks and sea-weeds in all climates.--_Obs._
The shells of this genus so closely resemble Patella that it is almost
impossible to make the distinction from the shells alone. They are,
however, generally flatter, and have the apex placed somewhat nearer
the posterior margin. The animals are very distinct. Fig. 231, P.
Antillarum.

PATELLOIDEA, Bl. or patelliform shells. The third family of the order
Monopleurobranchiata, Bl.; the animals of which are described as
depressed, flattened, covered by a wide external shell, which is
patelliform and non-symmetrical. This family contains the genera
Umbrella and Siphonaria.

PATROCLES. Montf. A genus of microscopic Foraminifera.

PATULARIA. Sw. A sub-genus of "Anodontinæ," Sw. thus described: "Shell
nearly equilateral, round or cordate; no teeth. P. ovata, Sw." _Ex._
_Conch._ pl. 36. rotundatus, Ib. pl. 137.

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

PAXYODON. Schum. HYRIA, Lam.

PECTEN. Brug. (_A comb._) _Fam._ Pectenides, Lam. Subostracea,
Bl.--_Descr._ Inequivalve, ribbed longitudinally, nearly equilateral,
with a triangular auricle on each side of the umbones; hinge linear,
destitute of teeth, having a central pit containing the cartilage;
muscular impressions one in each valve, large, sub-central.--_Obs._
This genus of beautiful shells, to which the well known Scallop
belongs, contains numerous species, some of which are found in the
British Seas. The Hinnites Pusio (P. Pusio of some authors) has been
separated on account of the irregularity of the external surface of one
valve. Fig. 171 to 173.

PECTENIDES. Lam. A family belonging to the second section of the order
Conchifera Dimyaria, Lam. including the following genera.

1. PECTEN. Unattached, including _Decatopecten_ and _Hinnites_.
Fig. 171, 172, 173.

2. LIMA. Unattached, gaping, Fig. 174.

3. PLAGIOSTOMA. Unattached, with an area between the umbones. Fig.
176.

4. DIANCHORA. Attached by the point of the umbo. Fig. 175.

5. SPONDYLUS. Attached, irregular, a triangular area in one valve,
divided by a slit. Fig. 177.

6. PLICATULA. Plicated, a very small area in one valve. Fig. 178.

PECTINATED. (_Pecten_, a comb.) Marked in a regular series of ridges.

PECTUNCULUS. (_Pecten_, dim.) _Fam._ Arcacea, Lam. and Bl.--_Descr._
Equivalve, sub-equilateral, orbicular, thick, covered with a velvety
epidermis, striated longitudinally; ventral margin denticulated within;
hinge semi-circular, with a series of small teeth on each side of the
umbones, which are separated by a small triangular disc in each valve
bearing the ligament; muscular impressions two in each valve, strongly
marked, united by an entire palleal impression.--_Obs._ Linnæan
conchologists have mixed this genus with Arca, from which it is,
however, totally distinct, not only in the roundness of the general
form, but also, and principally, in the curve of the hinge line; in
fact the characters of this genus are so strongly marked that there is
no danger of confounding it with any other. It does not contain many
species; two or three are British. The fossil species occur in London
Clay and Calcaire-grossiér. Fig. 134, P. pilosus.

PEDICLE or PEDUNCLE. (_Pedunculus_, a little foot.) The stem or organ
of attachment of the class of shells called in the system of Lamarck
"Pedunculated Cirripedes," consisting of a fleshy tendinous tube, by
the lower end of which they are attached to sub-marine substances.

PEDICULARIA. Sw. A genus of "Scutibranchia," thus described: "Shell
irregular, sub-patelliform; a thick, large, obsolete apex on one of the
longest sides, and an internal callous rim within, on one side only;
circumference undulated, irregular. P. Sicula, Sw." Sw. p. 357. Sicily.
A singular shell of the nature of Calyptræa, which is found attached to
corals, conforming its shape to the irregularity of their surface, and
fitting closely. _Ex._ Fig. 513.

PEDIPES. Adanson. _Fam._ Auriculacea, Bl. Colimacea, Lam.--_Descr._
Sub-globose, longitudinal, thick, striated; spire equal to the aperture
in length; aperture sub-ovate; peritreme sharp, thickened within,
modified by the last whorl; columella with three strong plaits on the
inner edge; outer lip with one fold.--_Obs._ This genus contains but
one or two small recent species, which in some respects resemble
Auricula, from which it is known by the thickness of its shell, and its
globular form. Fig. 299, P. Adansoni. Coast of Africa.

PEDUM. Lam. (_A shepherd's crook._) _Fam._ Pectinides, Lam.
Sub-ostracea, Bl.--_Descr._ Irregular, inequivalve, sub-equilateral,
attached by a byssus passing through a sinus in the lower valve; hinge
toothless, with a triangular area in each valve, separating the
umbones; ligament contained in a groove running across the area;
muscular impressions one in each valve, large, sub-orbicular; both
valves flat, narrow at the dorsal, broad at the ventral extremities;
lower valve with raised edges overwrapping the upper.--_Obs._ This
singular genus, of which only one species is known, differs from
Ostrea, not only in shape and structure, but also in the mode of
attachment, which is by means of a byssus passing through the lower
valve, in Pedum, but by a portion of the outer surface of the shell in
Ostrea. P. Spondyloideum (fig. 179) is the only species at present
known. Moluccas.

PEDUNCLE. See PEDICLE.

PEDUNCULATED. (_Pedunculus_, a little foot.) Attached to external
objects by a hollow fleshy tube, called the Peduncle.

PEDUNCULATED CIRRIPEDES. Lam. An order consisting of molluscs which
have multivalve shells, supported on a peduncle. The genera which it
contains are thus distinguished:

1. PENTELASMIS. Five valves. Fig. 34.

2. CINERAS. Five very minute valves distant from each other. Fig.
42.

3. OTION. The same, but the animal has two auricles. Fig. 43. The
genus Palmina, Gray, has but one.

4. OCTOLASMIS. Shaped like Pentelasmis, but with 7 or 8 valves.
Fig. 41.

5. LITHOTRYA. Five valves, peduncle scaly with a plate at the base.
Fig. 39.

6. SCALPELLUM. Shape square, valves 13, peduncle scaly. Fig. 35.

7. SMILIUM. Same, but the peduncle hairy. Fig. 36.

8. IBLA. Four valves, one pair long, one pair short, peduncle
hairy. Fig. 40.

9. BRISMEUS. Seven valves, even at the base. Fig. 38.

10. POLLICIPES. Principal valves in pairs, with many smaller valves
at the base. This genus has been divided into _Pollicipes_, and
_Capitellum_, the latter of which is founded upon Pollicipes
Mitellus, Auct. Fig. 37 and 37*.

PELAGUS. Montf. A genus composed of species of AMMONITES, which have
the spire covered by the last whorl, as in Nautilus and have an
umbilicus. ORBULITES. Bl.

PELLUCID. Transparent.

PELORUS. Montf. POLYSTOMELLA, Bl. A genus of microscopic Foraminifera.

PELORONTA. Oken. NERITA _Peloronta_, Auct. Fig. 330.

PENEROPLIS. Montf. A genus of microscopic Foraminifera.

PENICILLUS. Brug. ASPERGILLUM, Auct.

PENTALEPAS. Bl. PENTELASMIS, Auct.

PENTAMERUS. Sow. ([Greek: Pente], _pente_, five; [Greek: meros],
_meros_, part.) _Fam._ Brachiopoda, Lam.--_Descr._ Equilateral,
inequivalve; one valve divided by a central septum into two parts; the
other by two septa, into three parts; umbones incurved,
imperforate.--_Obs._ Dalman remarks upon his genus Gypidia, that it is
most probably identical with PENTAMERUS, Sow. but rejects the name for
two reasons; 1st. That it has already been applied to a class of
insects; 2nd. He disputes the fact of the shell being quinquelocular,
i.e. not counting the triangular foramen in the hinge of the larger
valve as one of the divisions. Fig. 212, 213.

PENTELASMIS. Leach. ([Greek: pente], _pente_, five; [Greek: elasma],
_elasma_, plate.) _Order._ Pedunculated Cirripedes, Lam.--_Descr._
Compressed, conical, composed of five valves; lower lateral pair
sub-trigonal; upper lateral pair elongated, sub-quadrate; dorsal valve
arcuate, peduncle elongated, smooth. Found on floating wood in the
sea.--_Obs._ This genus is known from all others of the order by the
number of valves. Pentelasmis is the genus Anatifera of Lamarck. Lepas
anatifer, Linn. Fossil species of this marine genus are found in the
Calcaire-grossièr of Paris, and in other similar beds. Fig. 34, P.
lævis.

PENULTIMATE WHORL. The last whorl but one.

PERA. Leach. A genus composed of CYCLAS amnica, and other similar
species.

PERDIX. Montf. DOLIUM _Perdix_, Auct.

PERFORATED. (_Perforatus._) Bored through, as the apex of Fissurella,
fig. 245, and Dentalium, fig. 2.

PERFORATION. (_Perforo_, to bore, or pierce.) A round opening, having
the appearance of being bored, as in Haliotis, fig. 338. Sometimes the
term is applied to an umbilicus which penetrates a shell through the
axis to the apex, as Eulima splendidula, fig. 348.

PERIBOLUS. Brug. A genus founded upon young specimens of CYPRÆA, with
their outer lips not formed.

PERIOSTRACUM. A name used by Mr. Gray to signify the substance which
covers the outer surface of many shells, called the _Epidermis_ by most
conchological writers. "Drap Marin" is the name given to this substance
by French Naturalists.

PERIPLOMA. Schum. _Fam._ Myariæ. A genus thus described: "Shell very
thin with the left valve more ventricose than the right; hinge
toothless, ligament double, the external portion thin, the internal
part thick, placed upon prominent, sometimes spoon-shaped hinge laminæ,
and supported by a transverse bone; muscular impressions two, distant,
palleal impression sinuated posteriorly." _Ex._ P. inæquivalvis. fig.
72. _Genus_, Osteodesma, Deshayes.

PERISTOMATA. Lam. A family belonging to the first section of the order
Trachelipoda, containing the following genera:--

1. AMPULLARIA. Globose or discoidal; operculum concentric;
including _Pachystoma_, _Lanistes_, _Ceratodes_. Fig. 318 to 320.

2. PALUDINA. Oval; operculum concentric. Fig. 321.

3. VALVATA. Globose; operculum spiral. Fig. 322.

PERISTOME. The edge of the aperture, including the inner and outer
lips.

PERITREME. A term used to express the whole circumference of the
aperture of a spiral shell. It is said to be notched or entire, simple,
reflected, round or oval, &c.

PERLAMATER. Schum. (_Mother of Pearl._) MELEAGRINA Margaritifera, Lam.
The pearl oyster.

PERNA. Auct. ("Pernæ concharum generis," Plin.) _Fam._ Malleacea,
Lam.--_Descr._ Sub-equivalve, irregular, compressed, foliaceous; hinge
straight, linear, composed of a series of transverse, parallel grooves,
containing the cartilage and intermediate spaces bearing the ligament;
anterior margin with a sinus for the passage of a byssus; posterior
ventral margin oblique, attenuated. _Obs._ This genus is known from
Crenatula by the straightness, number and regularity of the grooves in
the hinge and the sinus, for the passage of the byssus. Fig. 166, P.
Ephippium. Mostly tropical.

PERSICULA. Schum. A genus formed of MARGINELLA _Persicula_, Auct. and
other species having the spire concealed. Fig. 438.

PERSONA. Montf. (_Mask_). A genus composed of TRITON _Anus_, Auct. and
similar species. Fig. 401.

PETRICOLA. Lam. (_Petrus_, a stone; _cola_, an inhabitant.) _Fam._
Lithophagidæ, Lam.--_Descr._ Equivalve, inequilateral, transversely
ovate or oblong, rather irregular, anterior side rounded; posterior
side more or less attenuated, slightly gaping; hinge with two cardinal
teeth in each valve; muscular impressions two in each valve; palleal
impression entire; ligament external.--_Obs._ The Petricolæ are found
in holes made by the animals in rocks, madrepores, &c. They may be
known from Saxicava by the regularity of their form and the teeth on
the hinge. Fig. 91, 92.

PETRIFIED FINGERS, CANDLES, SPECTRE CANDLES, &c. are vulgar terms by
which fossils of the genus Belemnites were formerly known.

PHAKELLOPLEURA. Guild. A genus composed of those species of CHITON,
Auct. which have bunches of hairs or hyaline bristles on each side of
each valve on the margin. The Chiton fascicularis, found on our own
coasts, is a well known example. Fig. 506.

PHARAMUS. Montf. LENTICULINA, Bl. A genus of microscopic Foraminifera.

PHARETRIUM. König. ([Greek: pharetreôn], _pharetrion_, a
quiver.)--_Descr._ A testaceous body composed of two conical sheaths,
one within the other, perforated at the apex, and joined together near
the oral margin. P. fragile, fig. 3. In describing this genus, which
appears to be the same as ENTALIS of Defrance, Mr. König expresses the
supposition that it may probably belong to the class Pteropoda.

PHASIANELLA. Auct. (_Phasianus_, a pheasant.) _Fam._ Turbinacea, Lam.
Ellipsostomata, Bl.--_Descr._ Smooth, oval, variegated; aperture
entire, oval; outer-lip thin; inner-lip thin, spread over a portion of
the body whorl; columella smooth, rather thickened towards the base;
operculum horny, spiral within; testaceous, incrassated without.
Britain, Mediterranean, &c.; the fine large species are Australian.
Some fossil species are found in the tertiary beds.--_Obs._ The shells
composing this genus are richly marked with lines and waves of various
and delicate colours, and if the genus be restricted to those species
which are smooth, and which have a thick shelly operculum, we may
regard it as well defined; but there are some spirally-grooved species
of TURBO, Linn. which, from their oval shape, have been considered as
belonging to this genus. Such species should not, in our opinion, be
retained in this genus; they belong to Littorina. P. variegata, fig.
367.

PHITIA. Gray. CARYCHIUM, Müller.

PHOLADARIA. Lam. A family of the order Conchifera Dimyaria, Lam. The
animals contained in this family live in cavities bored by themselves
in rocks, wood, &c. They are cylindrical in form. Lamarck here places
PHOLAS and GASTROCHÆNA, the last of which belongs more properly to the
family of Tubicolaria, where we have enumerated it. Pholas has been
divided into _Pholas_, fig. 55, _Martesia_, which has the valves nearly
closed; and Pholadidæa, fig. 56, which has the cup-shaped extension.
The genus Pholadomya, fig. 67, has been added, although of doubtful
character. The genus Galeomma, fig. 58, 59, has also been recently
added.

PHOLADIDÆA. Leach. PHOLAS papyracea, Auct. Remarkable for the
cup-shaped process at the posterior extremity. Fig. 56.

PHOLADOMYA. Sow. (_Pholas_ and _Mya_.) _Fam._ Pholadaria,
Lam.--_Descr._ Thin, rather hyaline, equivalve, inequilateral,
ventricose, posteriorly gaping, elongated, anteriorly short, rounding;
ventral margin rather gaping; hinge with an elongated pit, and lateral
plate in each valve; ligament external, short, muscular impressions two
in each valve, rather indistinct; palleal impression with a large
sinus.--_Obs._ The only recent species of this genus is from the island
of Tortola. Several fossil species occur in rocks of the Oolitic
series. Fig. 57, P. candida.

PHOLAS. Auct. ([Greek: PHôleô], _pholeo_, to lie hid in a cavity.)
_Fam._ Pholadaria, Lam. ADESMACEA, Bl.--_Descr._ Transverse, oblong,
equivalve, inequilateral, imbricated, gaping on both sides, the
anterior hiatus being generally the largest, although sometimes nearly
closed, with the dorsal margin surmounted with one or more laminar
accessary valves; hinge callous, reflected, with a long curved tooth
protruding from beneath the umbones in each valve.--_Obs._ This genus
of marine shells, dwelling in holes formed in rocks, wood, &c. is
easily distinguished from any other nearly allied genus by the curved,
prominent, rib-like teeth. Fig. 55, P. Dactylus; 56. P. papyracea.

PHOLEOBIUS. Leach. Part of the genus SAXICAVA, Auct.

PHONEMUS. Montf. A genus of microscopic Foraminifera.

PHORUS. Montf. TROCHUS agglutinans, Auct. Remarkable for the adhesion
of little pebbles, dead shells, &c. to the outer edge of the whorls,
which are taken up in the course of the growth of the shell. From this
circumstance they are called "Collectors, Carriers, &c." Fig. 360.
Recent species are brought from the East and West Indies; fossil
species are found in the Tertiary beds.

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.

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.
100. 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 wing; [Greek: keras],
_ceras_, horn.) _Fam._ Ailées, Lam.--_Descr._ Turrited, oval,
ventricose, thick, tuberculated; spire short; aperture oval,
terminating in a lengthened canal at both extremities; outer lip
thickened, expanded, produced into horn-shaped, hollow, thickened
spires, with an anterior sinus apart from the canal.--_Obs._ This
genus, containing the shells commonly called Devil's Claws, Gouty
Scorpions, Spiders, &c. is distinguished from Strombus by the
digitations of the outer lip. No fossil species are known. Fig. 405, P.
aurantiaca.

PTEROCYCLOS. Benson. Syn. B. M. p. 133. A genus formed of species of
Cyclostoma, Auct. which have "a groove or hole at the hinder part of
the mouth."

PTEROPODA. Lam. ([Greek: Pteron], _pteron_, a wing; [Greek: pous],
_pous_, a foot.) The first order of the class Mollusca, Lam. consisting
of molluscs whose organs of locomotion consist of a pair of wing-shaped
fins. This order contains the genera Hyalæa, Clio, Cleodora,
Spiratella, Cymbulia, and Pneumoderma. To which may be added other
genera enumerated in explanation of figures 220 to 226. They may be
thus distinguished.

1. ATLANTA. Shaped like Nautilus, symmetrical. Fig. 220.

2. SPIRATELLA. Spiral, not symmetrical. Fig. 224.

3. CRESEIS. Straight, thorn-shaped. Fig. 222.

4. VAGINULA. Straight, widened in the centre; apex pointed. Fig.
225.

5. CUVIERIA. The same; apex blunt. Fig. 223.

6. CLEODORA. Aperture with three spines; apex recurved. Fig. 221.

7. HYALÆA. Vaulted, open extremity, three-cornered; apex
tridentate. Fig. 226.

PTEROPODA. Bl. The second family of Nucleobranchiata, Bl. the shells of
which are described as symmetrical, extremely thin, transparent,
longitudinally enrolled, either forwards or backwards. The animals are
remarkable for a pair of broad, flat, natatory organs or membranaceous
fins, from which the family derives its name. It contains, in the
system of De Blainville, the genera Atlanta, Spiratella, and Argonauta,
to which may probably be added PHARETRIUM, König; ENTALIS, Defrance.

PULLASTRA. Sow. _Fam._ Conques Marines, Lam.--_Descr._ Equivalve, ovate
or oblong, transverse, inequilateral; hinge with three diverging
cardinal teeth in each valve, notched at the terminations; muscular
impressions two in each valve; palleal impression having a large sinus;
ligament external, partly hidden by the dorsal margin.--_Obs._ This
genus includes the Venerirupes of Lamarck, and several species of his
Veneres, they are found in the sand on the shores of temperate and
tropical climates. Fig. 120, P. textile.

PULMONOBRANCHIATA. Bl. The first order of the first section of
Paracephalophora monoica, containing the families Limnacea,
Auriculacea, and Limacinea.

PULVINITES. Defr. (_Pulvinus_, a cushion.) _Fam._ Malleacea,
Lam.--_Descr._ Sub-equivalve, inequilateral, compressed, thin, slightly
gaping posteriorly; one valve flat, the other rather concave; hinge
linear, short, divided into perpendicular grooves; muscular impressions
two, one sub-central, the other above it, nearer the hinge.--_Obs._
This fossil shell is imperfectly known, and it is difficult to give a
sufficient reason for separating it from Perna. It comes from the
Baculite limestone of Normandy. Fig. 170, P. Adansonii.

PUNCTATED. (_Punctatus_, spotted or dotted.) For example, see Conus
Nussatella. Fig. 460.

PUNCTICULIS. Sw. A sub-genus of "Coronaxis," Sw. (Conus) described in
Swainson's Malacology, page 311.

PUNCTURELLA. Lowe. CEMORIA, Leach.

PUPA. Auct. _Fam._ Colimacea, Lam.; Limacinea, Bl.--_Descr._
Cylindrical, generally ribbed; spire long, obtuse, composed of numerous
slowly increasing whorls; aperture sub-quadrate, rounded anteriorly,
entire; outer lip thickened; columella plaited.--_Obs._ This genus is
composed of land shells very variable in form, differing from Bulinus
in the numerous slowly increasing whorls of the spire, and in the plicæ
on the columella, and from Clausilia in the want of a clausium.
Britain, Southern Europe, East and West Indies, Mexico, &c. P. Uva.
Fig. 291.

PUPELLA. Sw. A sub-genus of Clausilia. Lardn. Cyclop. Malac. p. 334.

PUPILLA. Leach. A sub-genus of Pupa, P. marginata, Auct. (Gray's
Turton, p. 196.)

PUPINA. Vignard. MOULINSIA, Grateloup. _Fam._ Colimacea, Lam.--_Descr._
Pupiform, sub-cylindrical; last whorl less than the preceding; surface
brilliantly polished; suture of the spire enamelled; aperture circular;
peritreme thickened; a notch at the base of the inner lip; operculum
horny, spiral.--_Obs._ The species upon which this genus was originally
founded, and described in the "Annal des Sciences Naturelles," tome 18,
p. 439, (December 1829,) is a small pupiform shell, having nothing to
distinguish it but the enamelled suture and the notch in the aperture;
characters quite insufficient in themselves for the purpose of generic
distinction; at the same time sufficient to lead M. De Ferussac to the
suspicion of its having an operculum. The next species, described by
Grateloup under the name of Moulinsia Nunezii, (Ann. Soc. Linn. Burd,
Nov. 1840), presents more remarkable characters, having the spire
turned backwards and the penultimate whorl disproportionately large.
Seven additional species have been lately brought to this country from
the Philippine Islands by Mr. Cuming. They will be described by the
author in the Zoological Proceedings for 1841, and an illustrated
monograph of the whole genus is published in the Thesaurus
Conchyliorum, Part I, by the Author. It may be observed that in one of
the new species, the notch in the peritreme almost disappears, leaving
a very slight sinus. Fig. 524, 526, 527, 528.