56 EOCENE MOLLUSCA. 



extremity of the siplional region, and ornamented with diverging ribs ; dorsal margin 

 straight, ventral margin slightly curved. 



Length. — 9 to 11 inches. 



Localities. — Highgate, Whetstone, Chalk Farm {Wetherett), Sheppey, Newnham 



[Prestwich), Bognor, {Edwards). 



Our shell is ornamented with about sixteen or eighteen rather elevated rays or costae, 

 slightly imbricated, and sometimes undulating, with occasionally a small intermediate ray. 



This species appears to have possessed a habit similar to that sometimes seen in 

 species of Modiola ; two or three specimens are found together, the one enveloping the 

 other. A young fry probably occupies the shell of its parent, which it has never left, and 

 perhaps grows to its full size where it was born, filling entirely with its own shell the one 

 previously occupied by the mother. Mr. Edwards' specimen shows this intimate union 

 of three individuals, each as nearly as possible of the same size. An imperfect specimen 

 of this species in the Museum of the Geological Society indicates a length of twelve 

 inches 



2. Pinna arcuata, /. Sowerby. Tab. XI, fig. 8. 



Pinna arcuata. J. Sow. Min. Conch., t. 313, fig. 3. 



— — Prestivich. Journ. Geol. Soc, 1847, p. 405. 



— — Morris. Catal. Brit. Foss., p. 180, 1854. 



— — TfOrbigmj. Prod, de Paleout., t. ii, p. 391, 1850. 



" Nearly equilateral, ventricose, finely ribbed, arched." 



Longest diameter, fths of an inch. 



Locality. — Highgate (.7. Sowerby). 



" Nearly as deep as long ; the hinge-line is gently curved ; the opposite edge much 

 arched ; in other respects, this strongly resembles the last." 



" Having several specimens of this arched Pinna from Highgate, exactly alike as well 

 in curvature as in size, I cannot but consider it a distinct species. It appears to be quite 

 different from P. incurva, Linn. : it occurs in Septaria." (Sowerby). 



The figure above referred to, and the description, are taken from 'Min. Conch.' 



3. Pinna margaritacea, Lamarck. Tab. XI, fig. 9. 



Pinna margaritacea. Lam. Ann. du Mus., t. vi, p. 218, and t. ix, t. 1", fig. 8. 



— — Befrance. Diet, des Scien. Nat., t. 41, p. "1. 



— — Desk. Coq. Fos. des En v. de Par., t. i, p. 280, pi. 41, fig. 15. 



— — Id. An. sans Vert, du Bassin de Par., t. ii, p. 35, 1860. 

 _ _ Nyst. Coq. Foss. Belg., p. 2/4, pi. 20, fig. 9. 



— /. Sow. in Dixon's Geol. of Sussex, pp. 94, 117, 172, 226. 



_ _ Horn's. Catal. Brit. Foss., p. 180. 1854. 



