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

both valves. Shell generally gaping at one or

   both extremities. This family includes the genera Anatina, Mya,

   Anatinella, Lyonsia, Myochama, Cleidotherus.

 

_Mactracea_ (plates, fig. 77 to 88), the cartilage placed in a

   trigonal pit, with a small external ligament. The genera Lutraria,

   Mactra, Crassatella, Erycina, Ungulina, Amphidesma, and Solenimya

   belong to this family, the last of which ought to have been placed

   among the Solenacea, as above.

 

_Corbulacea_ (plates, fig. 89, 90), inequivalve, with an internal

   ligament resembling the Mactracea, but differing in having one valve

   deeper than the other, although regular shells. This small family

   contains only the genera Corbula and Pandora.

 

_Lithophagidæ_ (plates, fig. 91 to 97), irregular, terebrating,

   living in holes of rocks. The genera are Saxicava, Petricola, and

   Venerirupis.

 

_Nymphacea_ (plates, fig. 98 to 110), ligament external, generally

   placed upon a prominent fulcrum, which passes from the inside to the

   outside of the hinge; valves generally gaping at the extremities. This

   family contains the genera Sanguinolaria, Psammobia, Psammotæa,

   Tellinides, Corbis, Lucina, Donax, Capsa, and Crassina.

 

_Conchacea_ (plates, fig. 111 to 121), regular, having several

   cardinal teeth and sometimes lateral teeth. The Conchacea constitute

   one of the most beautiful and numerous families of the class; they

   present equivalve shells, which are always regular, unattached, and in

   general closed, especially at the sides; they are always more or less

   inequilateral. They are divided into the _fluviatile_ and _marine

   Conchacea_, the first containing the genera Cyclas, Cyrena, and

   Galathæa, found in rivers; and the second, Cyprina, Cytherea, Venus,

   and Venericardia.

 

_Cardiacea_ (plates, fig. 122 to 130). This family, which resembles

   the last in some general characters, are also regular and equivalve,

   and are generally provided with radiating ribs, which are seldom seen

   in the Conchacea. The genera enumerated in this family are Cardium,

   Cardita, Cypricardia, Hiatella, and Isocardia.

 

_Arcacea_ (plates, fig. 131 to 138). These are known by having a

   row of numerous small teeth on the cardinal hinge in each valve. The

   genera included are, Cucullæa, Arca, Pectunculus, Nucula.

 

_Trigonacea_ (plates, fig. 139 and 140). It is doubtful whether

   this family should remain distinct. As of the two genera placed in it,

   the first, Trigonia, is thought by some naturalists to have strong

   affinities with Nucula, in the family of Arcacea; and the latter,

   Castalia, certainly belongs to the Nayades.

 

_Nayades_ (plates, fig. 141 to 152). These are fresh-water shells,

   covered on the outside by a thick horny epidermis, and pearly within.

   They include the genera Unio, Hyria, Anodon, Iridina.

 

_Chamacea_ (plates, fig. 153 to 155), inequivalve, irregular,

   foliaceous, attached; containing the genera Diceras, Chama, and

   Etheria.

 

Second Order, _Conchifera Monomyaria_.

 

Having one adductor muscle, and therefore only one impression in each

valve. They are separated into the following families:--

 

_Tridacnacea_ (plates, fig. 156 & 157), transverse, equivalve, with

   an elongated muscular impression, near the centre of the ventral

   margin; margin undulated at the termination of the radiated large ribs.

   The genera Tridacna and Hippopus are included.

 

_Mytilacea_ (plates, fig. 158 to 162), generally regular, with the

   hinge linear, without teeth, occupying the greater part of the dorsal

   margin. This family includes the genera Modiola, Mytilus, Pinna.

 

_Malleacea_ (plates, fig. 163 to 170), shell generally thin,

   inequivalve, irregular, foliaceous, with the hinge linear. This family

   contains the genera Crenatula, Perna, Malleus, Avicula, Meleagrina.

 

_Pectinides_ (plates, fig. 171 to 178). The Pectinides are generally

   regular or nearly so, with the shell solid; the greater part of them

   are auriculated at the dorsal margin, and generally characterized by

   ribs radiating from the umbones. The genera are Pedum, Lima,

   Plagiostoma, Pecten, Plicatula, Spondylus, Podopsis.

 

_Ostracea_ (plates, fig. 180 to 192). The shells of this family are

   irregular, generally attached and foliaceous. They compose the genera

   Gryphæa, Ostræa, Vulsella, Placuna, Anomia.

 

_Rudistes_ (plates 193 to 200). This family is composed of a

   particular association of shells, which appear on one side to be

   connected with the Ostracea; and on the other to approach the

   Brachiopoda. They differ from Ostracea in having no hinge or ligament,

   and only resemble them in their irregularity and foliaceous structure.

   The following six genera are placed by Lamarck in this

   family:--Sphærulites, Radiolites, Calceola, Birostrites, Discina,

   Crania. Of these, Calceola, Discina, and Crania are shewn to belong to

   the Brachiopoda.

 

_Brachiopoda_ (plates, fig. 201 to 219). The shells of this family

   are inequivalve, equilateral, and attached to marine bodies by a tendon

   passing through one of the valves. The animals have, near their mouth,

   two elongated, ciliated arms, which are spirally rolled when at rest.

   The following genera are enumerated by Lamarck, Orbicula, Terebratula,

   Lingula.

 

MOLLUSCA.

 

Lamarck applies, or rather restricts, this name to those invertebrated

animals, which while they are inarticulate in all their parts, have the

head sufficiently advanced at the anterior part of the body to be

distinguished; which is not the case with the Conchifera. All the shells

are univalve, and are divided into six orders, namely, the PTEROPODA, which

have wing-shaped natatory organs or fins, and have _light_, _thin

transparent_, _nearly symmetrical_ shells; the GASTEROPODA, with the foot

not distinguishable from the rest of the body, have _patelliform_, _open_,

and _scarcely spiral_ shells; the TRACHELIPODA with the foot distinct and

attached to the neck of the animal, have _spiral_, _non-symmetrical_

shells. The CEPHALOPODA, with arms covered by suckers surrounding the head

of the animal, have generally _symmetrical convolute_ shells. The

Cephalopoda are divided into _C. polythalamia_, which have the internal

cavity divided into chambers by septa, as in the Nautilus; and the _C.

Monothalamia_, which are not so divided, as the Argonauta. The order

_Heteropoda_ contains the genus Carinaria alone.

 

Order _Pteropoda_.

 

This order, containing hyaline, symmetrical, non-spiral shells, as above

described, is not divided into families, but contains the following genera,

Hyalæa, Cleodora, Limacina, Cymbulia; the first of which, although composed

of a single piece, resembles a bivalve so nearly, that Linnæus actually

placed it in his genus Anomia.

 

Order _Gasteropoda_.

 

With the exception of the genus Bulla and Vitrina, the last of which forms

a passage into the next order, the shells contained in this order are

_patelliform_, _open_, _and scarcely spiral_. They are divided into the

following families:--

 

_Phyllidiana_ (plates, fig. 227 to 231), containing the genera

   Chiton, Chitonellus, and Patella, the two former of which present the

   only exception to the statement above made, that all the shells of

   Mollusca were univalve.

 

_Semiphyllidiana_ (plates, fig. 232 and 233). Of the two genera

   contained in this family, Pleurobranchus is broad, thin, and slightly

   spiral at the apex, and Umbrella is flat, circular, with a central

   apex.

 

_Calyptracea_ (plates, fig. 234 to 246). The patelliform shells of

   this family, although united by no other general characters, are

   brought together by the characters of the animals which produce them.

   The genera are Parmophorus, Emarginula, Siphonaria, Fissurella,

   Pileopsis, Calyptræa, Crepidula, Ancylus.

 

_Bulleana_ (plates, fig. 247 to 253), contains the genera Bulla and

   Bullæa.

 

_Aplysiacea_ (plates, fig. 254 and 255). The genera Aplysia and

   Dolabella are both expanded, somewhat flattened shells, with the apex

   placed at one extremity, and slightly spiral.

 

_Limacinea_ (fig. 256 to 263). Many of the animals (slugs) are

   without shells; some, as the Limax, or common garden slug, have a

   slightly developed calcareous piece, hidden beneath the mantle, and of

   others the shells are scarcely spiral. The genera included in this

   family are, Parmacella, Limax, Testacella, Vitrina.

 

Order _Trachelipoda_.

 

All the remaining spiral non-symmetrical shells are arranged in this order,

which is divided into the following families:--

 

_Colimacea_ (plates, fig. 264 to 307). With the exception of the few

   contained in the family of Limacina, which ought not to be separated

   from this order, the whole of the land-shells are contained in this

   family, and although it is difficult to notice any one character by

   which terrestrial shells may be distinguished from others, few at all

   conversant with the subject are liable to mistake them. There is a

   general lightness and simplicity of form, which, though not clearly

   definable, is generally understood. The following distribution of

   genera by Lamarck, is generally acknowledged to require numerous

   modifications; the genera are Helix, Carocolla, Anostoma, Helicina,

   Pupa, Clausilia, Bulinus, Achatina, Succinea, Auricula, Cyclostoma.

 

_Lymneana_ (plates, fig. 308 to 312). The shells of this family are

   found in fresh water, wells, ditches, and ponds. They are of a light

   horny structure, and simple form. The genera Planorbis, Physa, and

   Lymnea are placed in this family by Lamarck.

 

_Melaniana_ (plates, fig. 313 to 317). These are also found in fresh

   water, principally in rivers; they are thicker than those of the last

   family; and the greater part of them have elevated spires composed of

   numerous whorls. This family contains the genera Melania, Melanopsis,

   Pirena.

 

_Peristomata_ (plates, fig. 318 to 322). These are also fresh-water

   shells, having opercula, and covered by a smooth green, or

   greenish-brown epidermis. They differ from the last family in having

   the peritreme entire. The genera are Valvata, Paludina, and Ampullaria.

 

_Neritacea_ (plates, fig. 323 to 333). The peculiarity of the shells

   of this family consists in the inner lip being flattened and rather

   straight at the inner edge. The genera are Navicella, Neritina, Nerita,

   Natica, and Janthina, the last of which forms an exception to the

   general character, and is placed by De Blainville in a family by

   itself.

 

_Macrostomata_ (plates, fig. 334 to 341), so named, on account of

   the large open aperture which they present in comparison to the spire.

   The shells of this family, which contains the genera Stomatia,

   Stomatella, and Haliotis, are pearly within.

 

_Plicacea_ (plates, fig. 342 to 344), contains the genera Tornatella

   and Pyramidella.

 

_Scalariana_ (plates, fig. 345 to 352). The genera Vermetus,

   Scalaria and Delphinula, seem to have been placed in this family by

   Lamarck, on account of the whorls being distinct from each other.

 

_Turbinacea_ (plates, 353 to 371). The shells contained in this

   family are all more or less globose, or angular, thickened and pearly

   within. The following genera are included in this division by Lamarck,

   Solarium, Rotella, Trochus, Monodonta, Turbo, Planaxis, Phasianella,

   and Turritella.

 

_Canalifera_ (plates, fig. 372 to 401). The numerous genera of

   which this family is formed, namely, Cerithium, Pleurotoma, Turbinella,

   Cancellaria, Fasciolaria, Fusus, Pyrula, Ranella, Murex, Triton, are

   distinguished by having at the anterior termination of the aperture, a

   more or less elongated canal.

 

_Alatæ_ (plates, fig. 402 to 406). These are known by having the

   outer lip more or less expanded and generally a posterior canal leaning

   towards the spire. The genera are Rostellaria, Strombus, and

   Pteroceras.

 

_Purpurifera_ (plates, fig. 407 to 429). In these, the canal, if

   such it may be called, is extremely short, and turning abruptly

   backwards, produces a kind of varix at the lower part of the whorl. The

   genera enumerated in this family are Cassidaria, Cassis, Ricinula,

   Purpura, Monoceras, Concholepas, Harpa, Dolium, Buccinum, Eburna,

   Terebra.

 

_Columellata_ (plates, fig. 430 to 433). The shells of this family

   are emarginated at the anterior extremity of the aperture, and the

   inner lip is characterized by plates or folds, which, with the

   exception of those on Columbella, are distinct. The genera are Mitra,

   Voluta, Marginella, Volvaria, Columbella, the latter of which would be

   better placed among the Purpurifera.

 

Convolutæ (plates, fig. 444 to 462). The well-known shells

   contained in this family are distinguished for the small proportion of

   the spire, if any, which remains uncovered by the last whorl. They

   might be well divided into two groups, the first containing the genera

   Ovulum and Cypræa, under the name of Cypræadæ, which are truly

   convolute, having the spire entirely hidden; and the second containing

   the genera Oliva. Ancillaria, and Conus.

 

Order _Polythalamous, or Chambered Cephalopoda._

 

The greater part of the shells belonging to this order are symmetrical, and

the internal cavity is divided into separate compartments, by plates called

_Septa_. It is divided into the following families:--

 

_Orthocerata_ (plates, fig. 463 to 470), containing the genera

   Belemnites, Orthoceras, Nodosaria, Hippurites, and Conilites.

   Hippurites certainly has no affinity with the Cephalopoda, but is

   ascertained to be a bivalve shell, properly belonging to the family

   Rudistes; the other genera are straight, elongated, and conical.

 

_Lituacea_ (plates, fig. 471), containing the genera Spirula,

   Spirulina, and Lituola, the two latter of which are microscopic.

 

_Cristacea_, containing the microscopic genera Renulina, Orbiculina,

   and Cristellaria.

 

_Spherulacea_, containing the microscopic genera Miliola, Gyrogona,

   and Melonia.

 

_Radiolacea_, containing the microscopic genera Rotalites,

   Lenticulina, Placentula.

 

_Nautilacea_ (plates, fig. 472 to 476). This family contains the

   following genera--Discorbites, Siderolites, Polystomella, Vorticialis,

   Nummulites, and Nautilus; the two latter of which alone are now

   received in cabinets of shells, the