TROCHUS. 531 



It inhabits various depths of water from five to fifty 

 fathoms, abounding most in from twelve to fifteen fathoms. 

 Though widely diffused through the Hebrides, Orkneys, 

 and Zetlands, it is not universally present in the regions, 

 but occurs in patches of variable extent. The localities in 

 which we have taken it most abundantly are Oban and 

 Lerwick in Zetland ; in the latter place it is frequent 

 among Modioli and Laminariee in seven fathoms water. 

 The British localities are in the southernmost bounds of its 

 range. It is an arctic species, ranging along the Scandi- 

 navian, Greenland, and Boreal American shores, and is 

 probably of western origin and comparatively late migra- 

 tion, as we do not find it fossil in British tertiaries. 



T. helicinus, 0. Fabricius. 



Small, smooth, thin, umbilicated. 



Plate LXVIII., fig. 4, 5, LXXIV. f. 10, and (animal) Plate CC. lig. 4. 



Turbo Helicinus, O. Fabr. (not Gmelin) Fauna Greenland, p. 393. — Phjpps, 



Voyage to North Seas, p. 198 (probably). 

 Trochus Neritoideus, Gmel. Syst. Nat. p. 3577. — Dillw. Recent Shells, vol. ii. 



p. 780. 

 Turbo margarita, Mont. Test. Brit. Suppl. p. 143. — Turt. Conch. Diction, p. 229. 

 — Lowe, Zool. Journ. vol. ii. p. 107, pi. 5, f. 10, 11. — 

 Fleming, Brit. Animals, p. 299. — Brit. Marine Conch, p. 1 69. 

 Helix margarita, Laskey, Mem. Werner. Soc. vol. i. p. 408, pi. 8, f. 5. — Flem- 

 ing, Encyclop. Edin. pi. 203, f. 9. 

 Pkorcus margarita, Risso, H. N. Europe Merid. vol. iv. p. 133, f. 47? — Mac- 



gilliv. Moll. Aberd. p. 134. 

 Trochus margaritus, Gray, Zoolog. Journ. vol. ii. (name only). — Johnston, Ber- 

 wick Club, vol. i. p. 265. 

 Margarita vulgaris, Leach, MSS. in Sowerby, Conch. Magaz. p. 24. — Sowerby, 

 Conch. 111. Margarita, f. 13. — Hanl. Brit. Marine Conch. 

 p. xxxvii. 

 „ arctica, Gould, Invert. Massach. p. 255, f. 173*. 

 „ Helicina, Moller, Index Moll. Grcenl. p. 8. — Lovkn, Ind. Moll. 



Scandin. p. 20. 

 „ margarita, Brown, Illust. Conch. G. B. p. 17, pi. 10, f. 28, 29. 



There are two forms of this shell, so apparently distinct 



