94 



CRETACEOUS LAMELLTBRANGHIA. 



Rounded depressions wliicli are found commonly on the casts of this and some 

 other species of /'')•//*' fi'oin tlie Cambridge Greensand are regarded by Seeley as 

 evidence of the occurrence of pearls. 



A specimen from the Gault (Plate XII, fig. 10) resembles P. oJiJoinja, but is 

 more convex between the umbo and the ])ostero- ventral exti-emity. 



Type. — In the Sedgwick Museum. 



DiMrihuilon. — Cambridge Greensand (derived). 



cnm. Cainbriclf^e Groonsanil (derived). Internal casts. Sedgwick Museum. Natm-al size, 

 Eg. E. — A. Pcnia oblonga, Soeley. The Type. — B, c, Perna, sp. (referred to I', lanccolata, Geinitz, 



Fict. 19. -Pf 



except fig ... . . . . 



by Seeley).— D, Perna semielliiitira, Seeley. The Type.— E, Pema, sp. (regarded by Seeley as a variety 

 of P. lanceolata, Geinitz) x 'i. — p, Penia, sp. (referred to P. sxibspathulala, Keuss, by Seeley). 



Perna sumiet.uptica, St'clci/, 18C1. Text-figure 19 d. 



1861 . Perna semielliptica, H. G. Seehy. Ann. Mag. Nat. Hist., ser. 3, vol. vii, 



p. 121, pi. vi, fig. 7. 



Bemarlcs. — This is distinguished from P. Rnuliniana (p. 02) by its relatively 

 greater length, larger apical angle, and more rounded outline. 



