312 CYPRINID.E. 



cardinals, of which the middle one is by far the largest, trian- 

 gular, and blunt ; the other two are laminar and diverge in 

 opposite directions, the anterior tooth being the slightest ; 

 lateral teeth as in the right valve : inside chalky-white, with a 

 thin superficial layer which is microscopically tubercular and 

 glistening ; margin thickened in front and at the sides, and 

 finely crenulated or notched : pallia! scar narrow, slightly im- 

 pressed: muscular scars irregularly elliptical or conchoidal, 

 very distinct. L. 1*1. B. 1*2. 



Yar. 1. paucicostata. Shell smaller, having fewer and 

 thicker ribs ; inside margin either smooth or notched. 



Yar. 2. Scotica. Shell usually rather compressed ; inside 

 margin thin and smooth. Venus Scotica, Maton and Rackett, 

 in Linn. Trans, viii. p. 81, t. 2. f. 3. 



Yar. 3. elliptica. Shell commonly still more compressed, 

 broader than long, in consequence of the posterior side being 

 more produced than in the typical form ; upper or dorsal slope 

 nearly straight ; ribs more or less evanescent in front and at 

 the sides ; inner margin smooth. Crassina ellvptica, Brown, 

 111. Rec. Conch, p. 96, pi. xxxviii. f. 3. A. elliptica, F. & H. 

 i. p. 459, pi. xxx. f. 8. 



Yar. 4. truncata. Shell more than ordinarily triangular ; 

 front margin nearly straight or truncate. 



Yar. 5. minor. Shell smaller and more convex. 



Yar. 6. trigona. Shell nearly as small as the last and de- 

 cidedly triangular. 



Yar. 7. incrassata. Shell obliquely triangular ; ribs more 

 or less evanescent in front and at the sides. Venus incrassata, 

 Brocchi, Conch. Foss. Subap. ii. p. 557, tav. xiv. f. 7. 



Yar. 8. multicostata. Shell somewhat triangular ; ribs nu- 

 merous. 



Habitat : Sand and mud, in 7-85 fathoms, on all our 

 coasts from Falmouth (Couch) to the Shetland Isles. 

 Captain Beechey dredged it in 145 fathoms off the Mull 

 of Galloway. It is most plentiful in the west of Scot- 

 land. Mr. Jordan has lately taken numbers of it in 

 Milford Haven ; but otherwise it does not seem to be 

 common in the south. A. sulcata occurs in many of the 



