BIVALVIA. 101 
have separated the two British shells in consequence of the very great difference in the 
tumidity or convexity displayed between them, and this difference appears to be constant. 
The Stubbington shell measures 2:th inches in diameter, with 1sths inch in depth or 
tumidity of the united valves, while the Bracklesham shell is longer than it is high, and it 
has a depth of less than an inch between the inflation of the two valves. There is also a 
difference in the hinge ; this latter shell has a narrower dental area, with a place for con- 
nexus also smaller. 
9. Pecruncuuus spissus, S. Wood. Tab. XVI, fig. 4, a, 3. 
Spec. Char. P. testa spissd, tumidd, globosd, orbiculari, equilaterali ; radiatim 
obsolete costellatd, costis depressis ; umbonibus prominentibus; ared conneaiis elongato- 
trigonatd, profunde sulcata ; margine dentali crassd, dentibus quatuor ad quinque, utroque 
latere transversalibus crassiusculis ; marginibus erregulariter crenulatis. 
Shell thick, tumid, globose, orbicular, equilateral, with depressed and obsolete ribs ; 
beaks prominent, area of connector broadly triangular, with deep chevron-formed lines ; 
dental margin thick, with 4 to 5 teeth on each side, inclining towards the extremities ; 
interior margins irregularly crenulated. 
Diameter, 1+ inch. 
Locality. Southampton (Ldwards). 
This species, I believe, is not rare; I have seen it only from one locality, and the 
specimens appear to be nearly all of the same magnitude, as if the full-grown shell, which 
I presume it to be, did not exceed the above dimensions. I have ventured to propose for 
this a new specific name, considering the characters to differ from those of any other 
species. ‘The nearest to which it approaches is P. g/obosus of the Bracklesham beds, but 
from which it appears to differ in having a more prominent umbo, and that shell has a 
more thickened dental area, with fewer teeth. 
10. PecruncuLus TEREBRATULARIS, Lamarck. Tab. XVI, fig. 10. 
PECTUNCULUS TEREBRATULARIS. Lamk. Ann. du Mus,, t. vi, p. 217, No. 3. 
— — Desh. Coq. foss. des Envy. de Par., t. i, p. 221, pl. 35, 
figs. 10, 11, 1829. 
Spec. Char. “ P. testd orbiculatd, subequilaterd, ventricosd, cordatda, incrassatd, radiatim 
sulcatd, sulcis planiusculis decussatis, cardine lato paucidentato ; dentibus lateralibus 
striatis.” 
Shell orbicular, nearly equilateral, ventricose, heart-shaped, thick, covered with radiating 
