TROCHUS. 



331 



to a rather sharp point : whorls 10-12, flattened, gradually 

 diminishing in size towards the apex : suture slight, defined 

 by the basal ridge of each whorl : moiiih rhomboidal, spread 

 out a little at the base of the pillar : outer Up thin : inner Up 

 pearly, and reflected on the pillar, which is extremely thick, 

 curved, and now and then furnished with a blunt tubercle ; 

 behind the pillar is an oblique and shallow excavation : imide 

 nacreous: operculum slightly concave, with a small central 

 pit, having from fifteen to eighteen turns, and microscopically 

 striated in the line of growth. L. 1. B. 1. 



Yar. 1. Li/onsii. White, with occasionally a purplish tip. 

 " T. Lyonsii" (Leach), Fleming, Brit. An. p. 323. 



Yar. 2. Jiumilior. Spire depressed. 



Yar. 3. Icevigata. Smooth and polished, with strong sutural 

 ridges, considerably expanded towards the base, and having a 

 depressed spire. T. Icevigata, J. Sowerby,Min. Conch. 1. 181. f. 1. 



Yar. 4. granulifera. ^Tiite, with the ridges granulated. 



Yar. 5. elata. Dwarf, having the spire elevated, a narrow 

 base, and the longitudinal striae flexuous. 



Monstr. Scalariform, with a rounded periphery and convex 

 base. T. discrepans, Brown, in Mem. Wern. Soc. ii. p. 519, 

 pi. xxiv. f. 4. 



Habitat : Rocks and stony ground, from low-water 

 mark to 85 f. ; common everywhere, especially in the 

 laminarian zone. The 1st variety is equally dififused, 

 although not so generally abundant ; the other varieties 

 are also occasionally white. Var. 2. Exmouth (Clark) ; 

 Bantry Bay (Humphreys); Oban (Barlee). Var. 3. 

 Anglesea (M*^ Andrew and Mrs. Hanmer Griffith); Loch 

 Carron (Barlee and J. G. J.). Var. 4. West coast of 

 Scotland; a single specimen (Barlee). Var. 5. Deep 

 water on the coasts of Antrim and Shetland (J. G. J.). 

 The monstrosity occurs with the ordinary form, but is 

 rare. Fossil in the Caithness boulder-clay (Peach); 

 Ireland (J. Smith); Norwich Crag (Woodward); Red 

 and Coralline Crag (S. Wood); Antwerp Crag (Nyst). 

 Its foreign distribution in a living state comprises all 



