PANDORA. 207 



Animal oval, compressed ; the mantle closed, except for 

 the passage of a narrow, tongue- shaped foot. Siphons very 

 short, united nearly to their orifices, which are divergent 

 and fringed. Branchiae of each side united into one. Labial 

 tentacles triangular. 



This curious and beautiful genus includes some fifteen 

 species, mostly exotic, though two of them range to our 

 shores. The margaritaceous aspect of the shell is a striking 

 character, and depends on a structure which has been in- 

 vestigated by Dr. Carpenter, according to whom " the 

 exterior presents a regular prismatic arrangement of cellular 

 tissue, the axes of the prisms being perpendicular to the 

 surface. Between these are distinct membranous partitions, 

 forming a tenacious membrane, that is left after decalcifica- 

 tion. The interior is truly nacreous." * In the animal of 

 this genus, according to Mr. Garner, -f- the only apj)earance 

 of the internal laminae of the branchiae consists of two very 

 narrow strips at the base of the others. 



P. ROSTRATA, Lauiarck. 



Form rather elongated, anterior end the broader, posterior end 

 attenuated and somewhat beaked ; ventral margin most swollen 

 in front and subcentrally ; hinder dorsal edge retuse, or incurv- 

 ed, and somewhat declining. 



Plate VIII. figs. 1 to 4. 



Tellina incequivalvis, LiNN. Syst. Nat. ed. 12, p. 1118.— Donov. Brit. Shells, 

 vol. ii. pi. 41, f. 1.— Mont. Test. Brit. p. 75.— Linn. 

 Trans, vol. viii. p. 50. — Turt. Conch. Diction, p. 172. 

 (not remarks). — Chemn. Conch. Cab. vol. vi. p. 115, 

 pi. 11, f. 106. — Speng. Beschaft Berlinisch. Ges. 

 Natur. vol. ill. pi. 7, f. 25 to 28. — Wood, General Conch, 

 p. 201, pi. 47, f. .2, 3, 4.— DiLLW. Recent Shells, vol. i. 

 p. 86.— Index Testaceol. pi. 5, f. 97. 



* Report Brit. Assoc, for 1846, p. 105. f Zool. Trans, vol. ii. p. 92. 



