A conchological manual — A Reader’s Guide

. 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.

3. _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.

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

5. _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.

6. _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:--

1. _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.

2. _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.

3. _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.

4. _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.

5. _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.

6. _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.

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

8. _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.

9. _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.

10. _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.

11. _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.

12. _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.

13. _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.