_Colours._--The white valves are edged with bright orange membrane; and are so close to each other that no interspaces, coloured from the underlying corium, are left. Peduncle, dark orange-brown, with the uppermost part under the capitulum bright orange all round; the chitine membrane itself being thus coloured. Sack, internally, dark purplish lead-colour. Body and cirri, either nearly white or pale purplish-lead colour, with the arms of the second, third, and fourth cirri, and pedicels of the fifth and sixth, more or less tinted with orange. A specimen preserved during fourteen months in good spirits had only a tinge of orange left round the orifice and round the upper part of peduncle, and on the cirri. In some other specimens, badly preserved, the chitine membrane was quite colourless, and sack and cirri dirty lead-colour. Fresh ova, peach-blossom-red; immature ova, in ovarian tubes, pale pink. _Monstrous Variety._--In Mr. Stutchbury’s collection, there was a specimen, with the scuta, broad, smooth, thin, and fragile, without any ridge running from the umbo to the apex, and with the occludent margin reflexed. This seemed caused by the shell having been attacked by some boring animal, and from having supported Balani. In the same specimen the first cirrus on one side was monstrously thick and curled; the second cirrus had its posterior ramus in a rudimentary condition. In Mr. Cuming’s Collection, there are small specimens with the zones of growth overlapping each other, with thick irregular margins, and with the carina distorted. This species has cost me much trouble: I have examined vast numbers of specimens, from a tenth to half an inch in length, attached to light floating objects, such as Janthinæ and Spirulæ from the tropical oceans, which all resembled each other, and slightly differed from the common appearance of _L. anserifera_: this variety is the _Pentalasmis dilatata_ of Leach; and for a long time I considered it as a distinct species. It differs from _L. anserifera_, in the less thickness of the valves, in their being more finely and yet plainly furrowed; in the greater width of the scuta; and more especially, of that part of the valve lying between the occludent margin, and the ridge running from the umbo to the apex; in the less elongation of the area in the terga, bounded by the two occludent margins; and, lastly, in the less size of the whole individual. The trophi and cirri are absolutely identical. Lately, however, in carefully going over a great suite of specimens, all the above few distinctive characters broke down and insensibly graduated away; and I am convinced that this form is only a variety of _L. anserifera_; its different aspect being caused partly by youth, but chiefly, I suspect, from being attached to light objects floating close to the surface of the sea.