3. Bulla. The Bubble. Eleven species. The great confusion that existed in this genus, as classed by Linnæus, has been elucidated by the division and classification of Lamarck. This genus derived its name from the resemblance which some of the smaller species have to a bubble of water. Its shells are found in almost all parts of the world. Shell external, oval, involuted; aperture very large, open the whole length of the shell, and generally wider at the base; outer edge sharp and smooth; summit umbilicated. Bulla lignaria. B. ampulla. B. striata. B. naucum. B. physis. B. fasciata. B. aplustre. B. hydatis. B. cornea. B. fragilis. B. solida. _B. aplustre._ The streamer-like Bulla. Pl. 17, fig. 7. Species completely involute; the spire very distinct, visible, but not projecting, with a kind of thickening at the anterior part of the columellar edge. _B. lignaria._ The woodlike Bulla. Species sub-involute, no visible spire either within or without, but narrowed towards the top when it is slightly umbilicated; yellowish brown colour, with transverse pale striæ. _B. hydatis._ The watery Bulla. Species more solid, thicker, almost entirely involute; whorls of the spire slightly visible in an umbilicus projecting interiorly from the summit. _B. naucum._ The sea-nut Bulla. Species thin; the whorls of the spire visible externally, but without projection, and with a suture as if caniculated without thickening at the anterior part of the columellar edge. _B. fragilis._ The fragile Bulla. Species very thin, rather involute; the whorls of the spire distinct within as without; the suture deep, angular, and cleft in a greater or less part of its length. FAMILY V. APLYSIACEA. Two genera. 1. Aplysia. Three species. This genus may almost be said to have no testaceous covering, as it appears more like the element of a shell. Aplysia depilans. A. fasciata. A. punctata. _A. depilans._ The bald Aplysia. Shell dorsal, semicircular, of a thin yellow cartilaginous substance. 2. Dolabella. Two species. Closely allied to the Aplysia; it is a singularly formed shell, difficult to describe, as it contains few of the characteristics which distinguish other shells. Shell rudimentary, entirely flat, sub-spiral, with a summit thick and very callous. Dolabella Rumphii. Dolabella fragilis. _D. Rumphii._ Rumphius’s Dolabella. Base thick, callous, and sub-spiral; dilated above, thin, and wedge-shaped.