ill 
PECTUNCULUS variabilis, 
TAB. CCCCLXXI. 
Spec. Char. Obliquely suborbicular, rather 
convex, finely striated longitudinally, be- 
coming smooth or suleated 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 - 
tin , par JBrongniart. p . 77, t. 6.J'. 16. 
This Pcctunculus varies perhaps more frequently than 
any other species in the proportion of its length to its 
breadth, and in its obliquity ; 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 striae, 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, Suffolk, and 
Essex; Parkinson refers it to the recent P, Qlycimeris. 
