306 trochidtE. 



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 Zi/9 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 : umhilicus rather wide and 

 bordered by a smooth broad lidge ; 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. B. 1-15. 



Yar. 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); 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 "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 



