PEARL-SHELLS.
Of the shelled Mollusca which the dredge ever and anon brings up, the Trochi are among the most conspicuous for beauty. T. ziziphinus is exceedingly common in deep water, and not rare within tide marks. Its very regularly conic form, and the blotches of dark purple that run in a spire round and round the shell are pleasing to the eye; and the animal, which crawls freely in confinement, is richly coloured, being of the tint of a ripe melon, striped with black. (See Plate I.) One or two specimens of a pure white variety of this species have occurred to me.
Though this is a shell of considerable size, it is exceeded in that respect, and (in the estimation of some probably), in that of beauty also, by T. granulatus. The latter is esteemed a somewhat rare shell, but in this Bay, and off Portland, it is not at all uncommon. In shape it is equally elegant with the former, the shell tapering to a conical point, and displaying a surface sculptured with spiral raised lines, each of which is composed of a number of minute rounded knobs, like a string of beads. Its texture is somewhat fragile, and its colour a faint flesh-tint or yellowish white, slightly dashed with purple.
In captivity the animal is rather chary of displaying itself; which is the more to be regretted since it is
minute Turris neglecta upwards, swarmed during the months of August, September and October in 1852; and it is generally considered that the latter part of summer and autumn is the most favourable season for studying all the Medusæ of our coasts.
