[66] Mr. Hancock, in his admirable account of his burrowing Cirripede, Alcippe lampas, (‘Annals of Nat. Hist.,’ Nov. 1849, p. 313,) came to this conclusion regarding the cup of Lithotrya, and hence was led to think that this genus did not form its own burrows, but inhabited pre-existing cavities. I am much indebted to this gentleman, who has been so eminently successful in his researches on the boring powers of marine animals, for giving me his opinion on several points connected with the present discussion.

[67] I owe to the great kindness of Prof. Steenstrup the sight of this Plate, published in the ‘Scientific Communications from the Union of Natural History,’ Copenhagen, January 30, 1850, No. I. Since this sheet has been set up in type, I have received from Prof. Steenstrup the memoir, in Danish, belonging to the figures in question; and the greater part of this has been translated to me by the kindness of a friend. My account of the means of burrowing is essentially the same as that published by Reinhardt; but the moulting of the scales on the peduncle, the presence of scales and of points of a different nature, the method of attachment by cement, the conversion of the discs into a cup, &c., seem not to have been known to this naturalist. Reinhardt states that the points on the peduncle will scratch Iceland spar, and that, apparently, they are formed of phosphate of lime: in the case of the closely-allied L. dorsalis, I must believe that the scales or beads on the peduncle are formed of carbonate of lime, for they were quickly dissolved with effervescence in acetic acid; and the star-headed points, which are subsequently developed under the calcareous scales, appeared to me, under the compound microscope, to be formed of a horn or chitine substance. Reinhardt states that the basal point of the peduncle is arched a little under the lowest disc, and there forms for itself a slight furrow (as represented in the lateral view, [Pl. VIII], [fig. 2]); but in the burrows examined by me, this furrow or depression did not really exist, the appearance resulting from the basal margin of the lowest disc, projecting beyond the wall of the cavity by the amount of its own slight thickness.

We will now proceed with our generic description.—

Animal’s Body.—This, as already stated, is partially lodged within the peduncle. The prosoma is rather largely developed.

The Mouth is placed at a moderate distance from the adductor muscle.

The Labrum is moderately bullate, with a row of blunt bead-like teeth, mingled with fine bristles, on the crest, which in the middle part is generally somewhat flattened.

The Palpi are blunt, and even squarely truncated at their ends; they are of large size, so that, if they had been half as large again, or even less, their tips would have met.

Mandibles ([Pl. X], [fig. 2]), with three nearly equal large teeth, and the inferior angle produced, broad, and strongly pectinated: in the interspaces between these teeth there are, in all the species, some very fine teeth or pectinations, which are seated a little on one side of the medial line. The mandibles are somewhat singular from the size of the transparent flexible apodemes (a a) to which the muscles are attached; these are oval and constricted at their origins: in L. dorsalis they are roughened with little points; in L. cauta and L. truncata they are large, of the same shape, but smooth.

Maxillæ.—These are larger, compared to the mandibles, than is usual with pedunculated Cirripedes; they differ in shape in the different species, being either nearly straight on their edge, and notched or not ([fig. 10]), or notched with the inferior part forming a double prominence ([fig. 12]); the spines on the inferior angle, which is sometimes slightly produced, are always crowded together into a brush, and are finer than those on the upper parts. The apodemes are less straight than is usual, and at their origin take, in all the species, a rather abrupt bend; their extremity is enlarged into a little disc, which in L. dorsalis is covered with strong points, but in the other species is, as usual, smooth.