M. BuUen Neivton — Egyptian Cretaceous Shells. 399 



OsTREA Thomasi, Peron. PI, XV, Figs. 8-10, 



Ostrea Brossardi, Coquand : " Mon. genre Ostrea Cretace," 1869, 



p. 45, pi. X, figs. 18, 19, non figs. 15-17. 

 Ostrea Thomasi, Peron, " Desc. Moll. Foss. Cretaces Tunisia " : 

 Explor. Soi. Tunisie, pt. ii (1891), p. 167. 

 Description. — Shell small, irregularly inflated, narrow, straight, 

 enlarged in rear but always tapering at the beaks ; lower valve 

 more convex than the upper, both ornamented with lamellose, 

 concentric, and often irregular striee, with no indication of radial 

 markings. 

 Dimensions. 



Lower valve — Height 27 mm. 



Length ... ' ... ... ... ... 21 ,, 



Diameter ... ... ... ... 10 ,, 



Several isolated valves of this small oyster are represented in the 

 Egyptian Collection, and they resemble in every detail Coquand's 

 figures (18 and 19) and agree with certain parts of his description, 

 as well as with the later account furnished by M. Peron. This 

 last-named author very properly separated two distinct forms which 

 Coquand recognized under the one name of 0. Brossardi, and 

 founded the species 0. Thomasi for the smaller specimens repre- 

 sented by Coquand's figures 18 and 19, which showed the tapering 

 beaks and were entirely without radial structure. 



Eemarks. — The species may be said to slightly resemble young 

 forms of 0. vesicularis and 0, Boiicheroni, and from the number 

 sent for determination it appears to be fairly abundant in Egypt. 

 The specimens are of a light-grey colour and entirely free from 

 matrix. The shell does not occur in Tunis, although its history has 

 been discussed by M. Peron. 



Horizon. — Turonian. 



Distribution. — Algeria ; west of the Gizeh Pyramids : Coll. 

 Geol, Surv, Egypt (No. 61, Box No. 29c). 



Genus GRYPH^A, Lamarck, 1801. 

 Syst. Anim. sans Vert., 1801, p. 398. 

 Type, — Gryphcea angulata, Lamarck. 



GRypH.^A CosTEi, Coquand. 



Ostrea Costei, Coquand : " Mon, genre Ostrea Cretace," 1869, 

 p, 108, pi. xsvi, figs. 3-5 ; pi. xxxviii, figs. 13, 14. 



GnjphcBa Costei, Stoliczka, " Cretaceous Pelecypoda Southern India " : 

 Mem. Geol. Surv. India, vol. iii (1871), p. 457. 



Ostrea Costei, Walther, " L' Apparition de la Craie environs 



Pyramides " : Bull. Inst. Egyptien, 1888, ser. 2, 



No. 8, p. 8. Peron, "Desc. Moll. Foss. Cretaces 



Tunisie " : Explor. Sci. Tunisie, pt. ii (1891), p. 140. 



Description. — Shell globulose, thick, sometimes longer than 



wide, and vice versa, and having a postero-lateral expansion ; lower 



valve very convex, with a large adherent surface, and ornamented 



