BTVALVIA. 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 Ifths 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 j this latter shell has a narrower dental area, with a place for con- 

 nexus also smaller. 



9. Pectunculus spissus, 8. Wood. Tab. XVI, fig. 4, a, b. 



Spec. Char. P. testa spissd, tumidd, globosd, orbiculari, aquilaterali ; radiatim 

 obsolete costellatd, costis depressis ; umbonibus prominentibus ; area connexus elongato- 

 trigonatd, profunde sulcata ; margine dentali crassd, dentibus quatuor ad quinque, utroque 

 latere transversalibus crassiuscidis ; marginibus irregulariter 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, \\ inch. 



Locality. Southampton {Edwards). 



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. globosus 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. Pectunculus terebratularis, Lamarck. Tab. XVI, fig. 10. 



Pectunculus terebratularis. Lamk. Ann. du Mus., t. vi, p. 217, No. 3. 



— — Desk. Coq. foss. des Env. de Par., t. i, p. 221, pi. 35, 



figs. 10, 11, 1829. 



Spec. Char. "P. testa orhiculatd, subaquilaterd, ventricosd, cordatd, incrassatd, radiatim 

 stdcatd, sulcis planiusculis decussatis, cardine lato paucidentato ; dentibus lateralibus 

 striatis." 



Shell orbicular, nearly equilateral, ventricose, heart-shaped, thick, covered with radiating 



