ANOMIA. 31 



iridescent: sculpture, scaly and sometimes prickly, minutely 

 striate in a longitudinal direction, and marked by irregular 

 lines of growth : colour white, with often a yellowish, pink, 

 rose-red, or brown tint : margins thin, rounded or wavy unless 

 contracted by position, nearly forming an obtuse angle behind : 

 beak straight and very small, not projecting beyond the dorsal 

 margin : cartilage short but strong, broad, semilunar, and 

 fixed in a cavity underneath the beak : hinge-line slightly 

 curved : hinge-plate thick and broad : orifice oval ; outer edge 

 reflected ; inside silvery and iridescent, sometimes having a 

 green tint, furnished in the lower valve at the hinge-end with 

 a thickened ledge to receive and support the cartilage : muscular 

 scar large, showing in the upper valve the impressions of three 

 inner portions of the muscle, which are nearly circular and 

 disposed in a descending but irregular line from the hinge, and 

 in the lower valve only one similar impression, which is placed 

 on the right hand of the observer : plug cylindrical, thick, and 

 longitudinally striate. L. 2-3. B. 2-5. 



Habitat: From low- water mark to 80 fathoms on every 

 part of our coasts, attached to shells, stones, sea- weeds, 

 and other substances. In a fossil state it occurs in our 

 newer tertiaries, as well as in the Coralline Crag, and 

 in the Italian pliocene deposits. It is likewise found 

 in the post-glacial beds of Bohuslan, Sweden, associated 

 with arctic shells. It is widely distributed in the Euro- 

 pean seas, from Iceland to the iEgean Archipelago ; and 

 its range also comprises Algeria, Madeira, North Ame- 

 rica, Russia, Lapland, and the Black Sea. Danielssen 

 has recorded it as having been dredged in the Scandi- 

 navian seas at a depth of 180 fathoms. 



In consequence of the lower valve being moulded on 

 the extraneous bodies to which it is attached bv the 

 plug, the upper valve partakes of a corresponding im- 

 pression, and the result is that the shell puts on a 

 Protean variety of shape. Bouchard-Chantereaux says 

 that out of two hundred specimens it is almost impos- 

 sible to find two exactly alike. When a specimen is 

 affixed to a Pecteii, Astarte, or other ribbed shell, it is 



