PLATE XxXxiV. 
Dissimilar as the several figures in this plate may appear, they are 
merely accidental varieties in size, growth, and colour of an individual 
species. ‘These shells are generally about an inch; or more, in length, 
and of a somewhat globose shape ; but so extremely irregular and dis- 
torted, that it can with difficulty be defined:, Dr. Wallace calls these 
shells the twisted pectines of Stroma, a little island that lies in the 
Pightland Frith ; he found them on some parts of the Orkneys, where 
he observed extraordinary cross and strong tides. The irregular form 
of these pectines rather surprised him. He adds, «‘ I cannot think the 
odd strange tumbling the tides make there, can contribute any thing 
to that frame; yet, after all, I never see them in any other place.” — 
These shells are now found on several of the English shores, as York-« 
shire, Scarborough, Mouth of the River Tees; and Dorsetshire ; and 
are also frequent in the fossil state, in the chalk pits of Kent and Surry. 
Both valves are convex, and much diftorted, but the under one is 
usually the most irregular ; the ribs are numerous, close set, longitu~ 
dinal, and prominent. The inside of the lower valve is smooth and 
white, when alive, and that of the upper has a pearly gloss. The 
outside is generally of a dingy white, or yellowish cast ; sometimes 
pale violet, or russety ; or white mottled, and varied with brown, 
or brilliant red. 
The ears of this shell are large, and nearly equal, but are often sa 
distorted as to appear much otherwise. It is proper to observe, that 
though the irregular form this shell assumes may be attributed to some 
injury it has sustained in its growth, every shell of this species is 
conftantly found with the same diftorted appearance. _ This circum 
{tance leaves no reason to doubt that such diitortions are characteriftic 
of this extraordinary and peculiar species. 
