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. 14. 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:--