ARCA. 181 



yellowish, irregularly mottled with reddish-brown : epidermis 

 light brown, filamentous, and forming rows of short leaf-like 

 bristles in the interstices of the longitudinal ribs, becoming 

 thicker towards the front and at the sides : margins rounded 

 on the anterior side, which is very short, flexuous in front, 

 wedge-shaped and pointed at the posterior side, where a sharp 

 keel runs obliquely from the beak to an acute angle at the 

 extremity of the posterior slope : byssal sinus long and wide : 

 beaks small, slightly recurved, and widely separate from each 

 other owing to the extent of the liga mental area : ligament 

 thin, of a golden-brown tint, lozenge-shaped and composed of 

 several strips or bands placed diagonally; ligamental cavity 

 very large and deep, usually smooth, but occasionally striated 

 by the impression of the ligament : hinge-line straight, forming 

 nearly a right angle at each extremity, its length equalling 

 the entire breadth of the shell : hinge-plate broad and strong, 

 considerably wider at the posterior extremity : teeth 40-50, 

 arched, perpendicularly striated on both sides and having their 

 crests consequently notched ; those on the posterior side are 

 the longest, and many of them are double : inside porcellanous, 

 partly stained with reddish-brown and green blotches ; margin 

 slightly crenulated, especially on the anterior side : pallial 

 scars flexuous : muscular scars oval, very large and conspicuous. 

 L. 0-85. B. 1-5. 



HABITAT : Rocky, stony, and shelly ground on all 

 our coasts and at all depths. In Bantry Bay it is not 

 uncommon at low water, closely wedged in the chinks 

 of slate-rocks, the shape being distorted and the surface 

 scraped in consequence of the confined position. The 

 abrasion is perhaps caused by the uneasiness of the 

 animal, through its continual endeavours to extricate 

 itself or change its place. In deeper water (20-90 

 fathoms) it occupies the crevices of large stones and the 

 hinge-cavities of old bivalve shells. In all cases it is 

 firmly attached by its byssus, and not a slight degree of 

 force will suffice to dislodge it. It is a Red and Coral- 

 line Crag fossil. The foreign distribution of this species 

 extends from Finmark to the ^Egean Sea on the east, 

 and to the Azores and Canaries on the west. Asbjorn- 



