DREDGING ON THE COASTS OF SHETLAND. 341 



means of the front part of its foot, very slowly and by an imperceptible 

 movement ; the other part of the foot was not pressed to the glass, but rested 

 on the mantle. The foot was occasionally twisted about and contracted, as if 

 through iineasiness. The animal was never wholly withdrawn into the 

 shell, although I irritated it with that object. The slit in the foot probably 

 serves for the admission of water into some tubular cavity or vessels which 

 permeate this organ ; this would have the effect of enlarging and swelling 

 the foot, so as to protect the Stilifer from being crushed by the spines of the 

 Echinus. A slight leverage or action of this kind at the base of the spines 

 would, of course, answer the piu'pose far better than a much stronger leverage 

 or power exerted at the top of the spines. The fry are enveloped in a gela- 

 tinous case. When detached and examined under a microscope, each had 

 three lobes, of which the two larger were in front ; these were finely eihated, 

 the cilia being rather long, and their points sometimes touching the surface 

 of the glass cell which contained the fry. The fry rapidly whirled them- 

 selves about by means of the ciha, but occasionally rested. They occupied 

 nautiloid shells of a single turn. 



Oue of the StUifers appeared to be fuU of spawn-masses, which were per- 

 ceptible with the microscope by reason of the shell being transparent. The 

 other Stilifer was a male. I afterwards replaced the latter in its old 

 quarters, where it was evidently more comfortable than in the glass tube ; 

 and it soon adhered to the sea-egg by the prehensile lobe of its foot, and 

 settled down among the spines. 



The cUiation of the body of Stilifer is also a characteristic feature of 

 Homalogyra (perhaps the living representative of Euomphalus), which is a 

 minute (but not microscopical) moUusk, without tentacles, and forms a 

 discoidal shell. It is an inhabitant of the European seas, and comprises two 

 species. Porbes and Hanley called one of these species Skenea nitidissima, 

 and the other Skenea rota. Dr. Fischer imagined that the first-named 

 species was the fry of some larger moUusk, because it was ciliated ; but he 

 must have either overlooked the fact, or else not have been aware, that in 

 all the species of Trochus, Bissoa, and other genera the tentacles are ciliated, 

 and also, in some species, other parts of the body. Mr. Clark was not more 

 happy in his conjecture that Homalogyra rota was the fry of Ccecum trachea, 

 the natui'al history of which this accomplished malacologist had so success- 

 fully investigated. I am not aware, indeed, that these shells or their animals 

 have any character in common ; besides which, it may be observed that the 

 operculum of Homalogyra is flat and paueispiral, with an excentric nucleus, 

 while that of Ccecum is more or less conical and multispiral, with a central 

 nucleus, as in Vermetus. (Since this paper was read, I have received from 

 the Marquis James Doria specimens of the young of C. trachea, which he 

 had dredged at Spezzia. The termiaal part or spire is very different from 

 that of H. rota.) 



The sexes in Stilifer appear to be separate, as may be seen from my 

 description of the animal of S. Turtoni, 



The shell of this species has been often described ; but I wiU briefly notice 

 some of its characters, which have not been satisfactorily stated. The spire, 

 for the fii'st three whorls, is cylindrical and narrow ; it then enlarges sud- 

 denly and disproportionately, and consists of three or four more whorls, 

 which are rounded and extremely ventricose or swollen. The apex or 

 nucleus of the spii-e is not reversed, although often set obliquely ; it projects 

 like the stump of a flagstaff which had been stuck in a slanting position on a 

 steep mound. The columellar lip, in adult and perfect specimens, is 



