CRANIA. 25 



Shell nearly round, with a square outline : upper valve 

 umbrella -shaped above, more or less compressed, rather solid, 

 of a dull aspect : sculpture, wrinkled by the circular marks of 

 growth, sometimes microscopically but irregularly striate lon- 

 gitudinally : colour reddish-brown or yellowish, with blotches 

 or faint streaks of the first-mentioned hue : margins thin and 

 sharp : beak very small, nipple-shaped, placed nearer the dorsal 

 end : lower valve of various degrees of solidity, according to the 

 age and quickness of growth, but the inside margin is always 

 broad, thickened, and raised, so as to form a ridge or rampart 

 round the enclosed space ; it is reticulated or closely pit- 

 marked within : muscular scars in both valves deeply marked. 

 L. 0-55. B. 0-5. 



Habitat : 18-90 fathoms, on almost every part of the 

 Scotch and Irish coasts, as well as in the seas of Shet- 

 land and the Orkneys ; Isle of Man (Forbes) . Abroad 

 it is distributed from Greenland to Vigo ; and I have 

 been unable to detect any difference between this species 

 and the C. ringens of Honinghaus, which is not un- 

 common in the Mediterranean and ^Egean Seas. Spe- 

 cimens from all the above localities vary much in shape, 

 and in the depth of the circular wrinkles or furrows, and 

 not less in the position and size of the muscular scars. 



Even the sagacious Muller was deceived by the strange 

 aspect of this shell. He placed it in the genus Patella, 

 having observed the upper valve only ; although he ad- 

 mitted that the animal (which he styled " vermis sin- 

 gularissimus ") differed toto coelo from a limpet, and 

 that the shell, on closer inspection, was not quite the 

 same. It is most singular that he overlooked the lower 

 valve. His comparison of the branching arrangement 

 of the arms to the dusky horns of a wild goat is not in- 

 appropriate. Sometimes the shell is ribbed . across or 

 obliquely, having taken the impression of an Astarte or 

 Pecten, on which it has been moulded. Being often 

 affixed to rugged stones or small pebbles, its shape is 



c 



t 



