AsfAitxE. MOLLUSCA. PSAMMOBIAD^E. 439 



497. P. polygona. — Subovate, with transverse and minute 



longitudinal striae ; retral extremity angular, and undulate at 



the margin. 



Tellina pol. Mont. Test. Brit. Sup. 27. t. xxviii. f. 4 — P. pol. Turt. Biv. 

 Brit. 96.— Frith of Forth Mr Laskey. 



Length half an inch, breadth a little more ; whitish ; anteally rounded ; 

 teeth, in one valve, two, large and distinct ; in the other a large triangular 

 bifid tooth, with an approximate small one. 



"- 498. P. strigillatus. — Oblong, striate in two directions on the 



anteal side, with one of the teeth oblique and laminar. 



Chama angusta, List. Conch, t. ccccxvi. — P. stri. Turt. Biv. Brit. 97« t; vi. 

 f. 13 Torbay and Cornwall. 



Length an inch, breadth 2 inches ; narrower at the retral side ; yellowish- 

 white ; ventral margin straight ; about 30 longitudinal striae. 



499. P- scopula. — Kidney-shaped ; striate in two directions 



on the l'etral side, with all the teeth erect. 



Turt. Biv. Brit. 98. t. G. f. 11, 12. Exmouth. 



Length three-eighths, breadth six-eighths ; glossy white It is distin- 

 guished from the last by the sides being more open where the valves are a 

 little reflected ; in the middle there is an evident contraction ; the oblique 

 .striae are not more than 20, the beaks are more prominent, and the teeth are 

 all erect, and close together. 



EXTINCT SPECIES. 



L P. solida.— Transversely elongated, depressed, tumid, nearly smooth, 

 slightly curved ; an obtuse carina marks the retral side.— Sower. Min. Conch, 

 t. 342. — Upper marine formation, Headon Hill. 



Gen. CXXIII. AST ARTE.— Suborbicular or transverse; 

 subinequilateral ; hinge with two diverging teeth ; a de- 

 pression before the beaks ; impression of the cloak entire, 

 exhibiting no syphon cicatrix. — This genus, instituted by 

 Sowerby (Min. Conch, ii. 85.), is identical with the subse- 

 quently announced Crassina of Lamarck. 



* Margm crenulated. 



500. A. sulcata. — Shell suborbicular, flattish, with broad, 

 concentric furrows, obsolete towards the beaks and sides. 



Venus sulcata, Mont. Test. Brit. 131. — England, and north of Scotland. 

 Diameter about seven-eighths of an inch ; white, with an opake brown cu- 

 ticle ; strong and thick ; beaks prominent, inclining, under which is a lanceo- 

 late depression ; cartilage side likewise depressed, but narrower, exterior 

 margin rounded ; inside white, smooth and glossy at the margin, the middle 

 dull and rough ; edge crenulated ; hinge with three teeth in one valve, the 

 middle one larger than the others, with a deep cavity in one valve, into which 

 the two teeth of the other valve lock. Montagu states his having received 

 this shell as English from Mr Sowerby, and that according to Mr Swainson, 



