Ill 



PECTUNCULUS variabilis. 



TAB. CCCCLXXI. 



Spec. Char. Obliquely suborbicular, rather 

 convex, finely striated longitudinally, be- 

 coming smooth or sulcated by wear ; teeth 

 of the hinge and lines upon the area of the 

 ligament, numerous; beaks short nearly, 

 close. 



Syn. p. pulvinatus var. Taurinensis. Mem. 

 sur. les Terrains de Sediment sup. du Vicen- 

 tiuy par Srongniart, p. 11 y t. Q.f. 16. 



This Pectunculus varies perhaps more frequently than 

 any other species in the proportion of its length to its 

 breadth, and in its obhquity ; sometimes it is even longer 

 than wide, but it is always longer and more oblique than 

 P. pilosus, and has a more regularly curved edge. It is 

 nearly like P. pulvinatus, but is never so convex, and is 

 distinguished at first sight; neither will it agree with the 

 description of P. Cor. given by Lamarck. The hinge 

 teeth are generally numerous, but are liable to be ob- 

 literated by the area of the ligament, so that in old shells 

 but a few remain on each side : the beaks are not ob- 

 lique. When young and not worn, it is covered with 

 very fine longitudinal stries, these soon wear away, and 

 leave the surface smooth ; by decay the internal ribbed 

 structure, common to shells that have teeth in their 

 margins, is displayed, with a strong resemblance to lon- 

 gitudinal sulci. 



Not having been able to refer this well known English 

 Crag shell to any of Lamarck's or Brocchi's species, I 

 have been obliged to give it a new name. It may pos- 

 sibly have been considered by Lamarck as a variety of 

 his P. Cor but this wants proof. His P. obovatus I 

 believe occurs in the Suffolk Crag, but specimens alone 

 can decide. 



Very common from half an inch to three inches or more 

 long, in many of the Crag pits of Norfolk, Sufiblk, and 

 Essex ; Parkinson refers it to the recent P. Glycimeris. 



