ANOMTA. 335 



of shelly matter which surmounts the aperture of the lower 

 valve. 



The shape of the shell, although variable, is usually 

 more or less suborbicular, and has a tendency rather to 

 increase in width than length. In the younger and more 

 beautiful individuals the exterior is adorned with a warm 

 tinge of reddish brown upon the interstitial spaces of the 

 costas. The valves are generally more or less compressed, 

 and the upper displays upon the central disk or area inter- 

 nally (and in the young externally likewise) a darker or 

 lighter tint of bluish green. The beak is prominent, but 

 is not (as in epMppium) immediately adjacent to the 

 margin. The perforation, which is large in the most cha- 

 racteristic examples, seems rarely if ever oblique, is usually 

 somewhat pear-shaped, and is divided from the edge of the 

 outer valve by a comparatively broad space of shelly 

 matter. t 



We have never seen examples which emulate the dimen- 

 sions attained to by the preceding species ; one of our 

 largest, which appears from the solidity of the upper valve 

 to be aged, measures only a full inch and a half in breadth 

 and rather less in length. 



This form has a greater range in depth than any of our 

 other Anomicc beginning in the Littoral and Laminarian 

 regions, and living in some places, as off Cape Clear in the 

 south and Cape Wrath in the north, as deep as forty-five 

 and fifty fathoms. It is more abundant in the north and 

 west than in the south, and on the whole is not so common 

 as the preceding forms. It adheres closely to shells and 

 stones, and ranges throughout the northern shores of 

 Europe. 



