242 ARCADE. 



the latter at the sides, and towards the lower margin of the 

 shell. The straight dorsal margin is very nearly equal in 

 length to the ventral, which latter is greatly arcuated, and 

 ascends so remarkably, yet in a convex line, in front of the 

 shell, as to excise, as it were, the lower anterior corner, and 

 more or less sharply angulate the upper one. The posterior 

 termination is broad, well rounded below, and above forms 

 a more or less distinct obtuse angle ; the hinder edge, and 

 particularly its lower portion, curves outwards. The 

 umbones are j^rominent ; the beaks, which are small, 

 and not much inclined, are approximate, the cardinal 

 area being extremely narrow. There is no angulation 

 of the umbonal ridge, nor any concave area behind it. 

 The interior is of an uniform white ; the hinge teeth, of 

 which none exist in the middle part of the margin, only 

 number three or four in front, and three behind : the latter 

 are jjeculiarly oblique, the former decidedly large for the 

 size of the shell. The internal margin is not distinctly 

 crenated, but some obscure crense occasionally appear at 

 the narrower extremity. From the minute size of the 

 species, the epidermidal covering is not very distinct ; it 

 seems, however, of a brownish ash-colour, and not pilous, 

 but membranaceous. Our largest specimen only measures 

 about two lines at the broadest part, and is rather more 

 than the fifth of an inch in length. 



The animal is of a white colour : otherwise unknown. 



The Area raridentata was first discovered in a living 

 state by Mr. M 'Andrew, who dredged it in the Minch fifty 

 miles from the Shiant Isles, among the Hebrides, in fifty 

 fathoms on a bottom of sandy gravel, and afterwards twenty 

 miles off the west of Zetland in sixty fathoms, and near Foula 

 in forty-five. Mr. Jeffreys has taken it in forty fathoms 

 off Skye, and Mr. Barlee in the outer Hebrides. Far 



