138 PROCEEDINGS OF THE MALACOIOGICAL SOCIETY. 



Mr. Henry "Wood refers, also, to this subject, and supplies woodcuts 

 of two additional specimens (figs, b and e) as well as a new figure of 

 Professor Seeley's type, the whole of which material is in the 

 Sedgwick Museum at Cambridge. 



Geological age. — Albian (commonly called the Cambridge Greensand, 

 which is a phosphatic derivative deposit). 



Locality. — Cambridge. 



Collection. — British Museum [L. 9062]. 



Family OSTREID^. 

 Geyph^a dilatata, J. Sowerby. PI. IV, Fig. 6. 



Gryphma dilatata, J. Sowerby: Min. Conch., 1816, vol. ii, pi. cxlix. 

 Gryphcea, Z . M.oxv\?, : Ann. Mag. Nat. Hist., 1851, vol. viii, p. 89, 

 pi. iv, fig. 16. 



A Jurassic example of pearl-growth is met with on the interior of 

 a lower valve of Gryphcea dilatata, which assumes an elongate, 

 irregular, somewhat pyriform body, measuring 20 by 13 mm., and 

 adherent in great part to the adductor muscular scar region, and, as 

 mentioned originally by Morris, it is free at both ends. The external 

 lamina of this specimen is continuous with the shell, whilst the outer 

 layers are said not to exhibit the usual fibrous character of a peiiaceous 

 concretion, having probably been altered by subsequent mineralization. 



The valve on which this specimen is adherent has a length of 70 mm. 

 and a height of 85 mm. 



Geological age. — Jurassic (Kimeridgian), found in the Drift. 



Locality. — Muswell Hill, near London. 



Collection.— Bxxii^'k Museum (N. T. Wetherell Coll.) [L. 21230]. 



EXPLANATION OF PLATES. 

 Plate IV. 



Inoeeramus Goldfussianus , Orbigny. 



Senonian (Campanian) : Haldem, Westphalia. 



Fig. 1. — Natural cast of the interior of a left valve with a fragment of original shell 

 in situ, showing numerous rounded pittings caused by pearly protuberances on 

 the original inner surface of the valve. Eeduced | from the original fig. 4<f in 

 the " Petrefacta Germanise." 



Inoeeramus expansus, W. H. Baily. 

 Senonian (Campanian) : Pondoland, S.E. Africa. 



Fig. 2. — Natural cast of a fragmentary left valve showing a series of rounded 



pittings. f nat. size. [British Museum, L. 8644.] 

 Fig. 3. — Natural cast of another specimen showing both valves in the closed 



condition, studded with numerous pittings as before, f nat. size. [British 



Museum, L. 8644.] 



Inoeeramus sagensis, D. D. Owen, var. quadrans, E. P. Whitfield. 



Senonian: near Burlington, New Jersey, United States. 



Fig. 4. — Natural cast of the interior of a left valve, showing numerous rounded 

 pittings and fine radial striations, copied from Whitfield's original fig. 16 

 published in 1885. f nat. size. 



