TROCHUS. 297 



cata. The spawn is deposited on sea-weed and the 

 under side of stones ; each egg is enclosed in a yellow 

 membranous capsule, all of which are agglutinated 

 together at their sides and form an irregular glairy 

 mass. I counted above 1 00 eggs in one of these spawn- 

 masses. The fry are clear white, and not unlike the 

 young of Cyclostrema serpuloides. The shells of the 

 two sexes are different, as will appear from my descrip- 

 tion. The globular form of the female, with the outer 

 circumference of each whorl embellished not only by the 

 invariable lustre, but occasionally by a variety of 

 glowing tints, reminds us of the vision of Panthea in 

 ' Prometheus Unbound/ in which were displayed 



" Purple and azure, white, green and golden, 

 Sphere within sphere." 



The shell is sometimes twisted or otherwise distorted. 

 Zetlandic are much larger than English or Irish speci- 

 mens; those from the Arctic Sea are comparatively 

 giants. I dredged a specimen empty, but having the 

 operculum in it, about 25 miles north of Unst in 80 

 fathoms ; it was pierced, apparently, by some animal 

 which had probably carried it off and dropped it in 

 the far deep, after extracting the mollusk through the 

 hole. 



According to Fabricius this is the Turbo neritoideus 

 of Olafsen. The Trochus helicinus of Gmelin (from 

 Knorr and Chemnitz) is a large West-Indian shell, but 

 still undetermined. Our species is the Helix margarita 

 of Laskey, Turbo inflatus of Totten, Trochus margaritus 

 of Gray, Margarita vulgaris of Leach (fide Sowerby) 

 and certainly his Margarites diaphana, Margarita heli- 

 coides of Beck (fide Sowerby), and M. arctica of Gould. 

 It is difficult to guess what was the M. arctica of Leach, 

 described in the "Appendix No. II." to Sir John Ross's 



o5 



