Natica glaucina. N. albumen. N. mamillaris. N. mamilla. N. ampullaria. N. canrena. N. cruentata. N. millepunctata. N. vitellus. N. helvacea. N. collaria. N. monilifera. N. labrella. N. rufa. N. uni-fasciata. N. melanostoma. N. aurantia. N. conica. N. plumbea. N. lineata. N. fulminea. N. maculosa. N. vittata. N. castanea. N. Marochiensis. N. arachnoidea. N. zebra. N. zonaria. N. Chinensis. N. Javanica. N. cancellata. _N. canrena._ The Canrena Natica. Sub-globular, smooth, umbilicus deep, bordered anteriorly by a kind of callous column; spire a little prominent; exterior fawn coloured, with bands and rays of reddish brown; interior white; operculum calcareous. _N. castanea._ The chestnut Natica. Pl. 21, fig. 6. Species with the umbilicus uncovered, and the operculum horny. _N. mamilla._ The nipple Natica. Species with the umbilicus entirely covered over by a large callosity; the spire papillose, and the operculum horny. 5. Janthina. Two species. Formerly classed with the Helix, which it somewhat resembles in form, but properly separated, as it differs in every other respect. It is a singular marine shell, often found in great numbers floating on the surface of the sea, suspended by a vesicular appendage, which stains the hand of a purple colour. Shell sub-globular, ventricose, extremely thin and fragile; transparent, of a beautiful violet colour; the spire low, lateral, pointed, with sub-carinated whorls; aperture large, sub-angular, greatly modified by the last whorl of the spire; edges disunited, the left entirely formed by the columella, which is straight and continued beyond the base, the right edge sharp, often with a sinus in the middle. Janthina communis. Janthina exigua. _J. communis._ The common Janthina. Pl. 18, fig. 6. Very fragile, aperture triangular, with a small notch on the margin of the outer lip; beautiful violet colour. FAMILY XII. MACROSTOMIDES. Four genera. 1. Sigaretus. Four species.