346 GENUS — LITHOTRYA. 



power of enlarging its cavity, how does it first bore down 

 into the rock ? It is quite certain that the basal cup is 

 absolutely fixed, and that neither in form nor state of 

 surface it is at all fitted for boring.* I was quite unable 

 to answer the foregoing question, until seeing the ad- 

 mirable figures by Reinhardt f, (PL VIII, figs. 2 and 2 a) 

 of L. Nicobarica, still attached in its cavity. Subsequently 

 I obtained from Mr. Stutchbury several pieces of rock 

 completely drilled with holes, many of small diameter, by 

 L. dorsalis, and in these I found numerous instances of 

 the linear rows of little discs, like those of L. Nicoharica, 

 showing in the plainest manner, that each time a new disc 

 is formed, that is, at each exuviation, the animal moves a 

 short step downwards; and as the lowest of these little discs 

 in none of the burrows was placed at the very bottom, we 

 see that the lowest point of the peduncle must be the 



* Mr. Hancock, in bis admirable account of bis 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. 



f 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 horny 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. 



