306 trochidjE. 



in the interstices of the ridges ; the base of the shell is en- 

 circled by a much stronger and more prominent ridge, giving 

 that part a keeled or angulated appearance, and the upper 

 part of each whorl is frequently puckered lengthwise : colour 

 pale yellowish-white, beautifully variegated or painted by 

 short longitudinal streaks of pinkish-red or (rarely) purple : 

 spire not much raised ; apex small and pointed : whorls 8, 

 regularly enlarging : suture deep and channelled : mouth very 

 oblique, in consequence of the upper lip being placed far in 

 advance of the lower: outer lip often broken and jagged: 

 inner Up very thick, folded above over that part of the umbi- 

 lical cavity, and furnished in the middle with a slight tooth - 

 like projection : inside nacreous : umbilicus rather wide and 

 bordered by a smooth broad ridge ; it is very deep and shows 

 all the inner spire : operculum having from 12 to 15 volutions, 

 becoming somewhat concave towards the centre, the under 

 side of which has a minute boss or point ; each volution is 

 microscopically striated in an oblique and somewhat curved 

 direction. L. 0*85. JB. 1-15. 



Var. alba. Shell of a uniform white. 



Habitat : Rather common, from low-water mark to 

 40 f., in the southern and western counties of England, 

 the Channel Isles, Bristol Channel, Ireland, west of 

 Scotland, and the Orkneys and Shetland; Anglesea 

 (Pennant) j Isle of Man (Forbes) . It does not appear 

 to be a native of our eastern or north-eastern coasts, 

 although Mr. Bean found a dead specimen at Scar- 

 borough. Sir Cuthbert Sharpe included it in his list 

 of Hartlepool shells ; and Miss Backhouse is said to 

 have met with it at Seaton Carew, Durham. I agree 

 with Mr. Alder in believing that these specimens may 

 have been introduced in ballast. The variety occurs at 

 Oban, Skye, Ullapool, and Lerwick. T. magus is fossil 

 in the u post-pleistocene beds" at Belfast (Grainger), 

 Clyde beds and Ireland (Smith), Strethill (Maw); higher 

 and older deposits, 400-440 feet, in the Christiania 

 district (Sars); Antibes (Mace); Subapennine tertiaries 



