PLATE XXXIV. 



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 pectlnes 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 pectlnes 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 m 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 so 

 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- 

 ftance leaves no reason to doubt that such diftortions are characteriftic 

 of this extraordinary and peculiar species. 



