"First, the genera with the canal ascending, or turned towards the back of the shell-- _Cassidaria_, } _Cassis_, } _Buccinum_, helmets. "_Cassidaria_ is not a very common genus; but the helmets, _Cassis_, are both numerous and plentiful in most collections. The straight aperture slightly reminds you of a _Cypræa_ perhaps, but the short canal, abruptly turned back, is a clear distinction; the right-margin generally toothed; the columella folded, or wrinkled, transversely. "_C. cornuta_, _C. flummea_, _C. arèola_ and _vibex_, are all well-known species, _C. cornuta_ has large tubercles like horns round the tip of the shell. _C. arèola_ is marked with chequers. _C. rufus_, from the Moluccas, is a fine shell, with a deeply coloured red aperture. "In the next division the canal is oblique, and directed backwards. [Sidenote: NASSA. RICINULA. PURPURA.] _Ricinula_ _Murex_. _Purpura_, } _Monoceros_, } _Concholepas_, } _Harpa_, } _Buccinum_. _Dolium_, } _Buccinum_, } _Eburna_, } _Terebra_, } "To these genera another has been added, called _Nassa_, of which _Buccinum arcularia_ will furnish an example. The columella has a callosity very evident in the species _Pullus_ and _Thersites_. "_Ricinula horrida_ has a ringent aperture of a fine violet colour; the shell is thick, and covered with large black tubercles. The genus takes its name from a resemblance to the seeds of _Ricinus_. "_Purpura_ is a large genus: in certain of the species the colouring-matter exists of which the ancients formed their famous purple dye. It is the last genus that offers any appearance of a canal at the base of the aperture. "_P. patula_, the scoop, from the Atlantic and Mediterranean, has the aperture remarkably dilated, the margin sulcated. "_P. lapillus_ is a common British shell among the chalk-cliffs of the coast; the colour varies, sometimes white, at others yellowish. [Sidenote: MONOCEROS. CONCHOLEPAS. HARPA.] "I shall describe a species of the singular genus _Monoceros_, by which you will scarcely fail to recognise it. "The columella is flattened like _Purpura patula_; just within the outer lip is a row of small teeth; but the principal peculiarity is a process, or horn, near the outer part of the lower lip, and close to the canal, from which the genus derives its name _Monoceros_, _one-horn_. It is brought from the seas of America. "_Concholepas Peruviana_, the only species, is also a remarkable shell. The aperture is very large, almost equal to the shell itself; the spire is near the edge; the outside is marked with ribs, or costæ; there are two short teeth on the right-margin. This shell was placed among the _Patella_.