64 R. BULLEN NEWTON on 



Nigeria, however, is considerably smaller than such giant forms, and appears 

 to be more closely related to O. aginensis, 1 with which it agrees partially in 

 size, shape and sculpture, as figured by Goldfuss 2 under the name of O. 

 crispata (pars), but differing in possessing a greater width of ligament region 

 and in the ventral position of the much larger and rounder adductor scar 

 marking, which is higher up and very posteriorly situated in O. aginensis. 

 Moreover, if M. Cossmann and Peyrot's 3 interpretation is correct, the valves 

 of O. aginensis are distinctly narrower, the height being nearly three times 

 the length, and with no indication of radial costae on the upper valve. 

 These very elongate oysters have been recognised by Dr. Sacco under his 

 genus Crassostrea, founded on Gmelin's Ostrea virginica (Moll. Terz. 

 Piemonte, &c., 1897. Vol. 23, p. 15). 



Represented, also, in the collection, are the remains of a very large, 

 presumably upper valve of this oyster, which have been united, thus exhibiting 

 a fair proportion of the anterior side of the shell, including a massive, thick, 

 and broad laminate margin, with parts of a nacreous, moderately shallow 

 inner surface, which shows an upward curvature on the dorso-posterior side 

 and therefore indicating the probable extent of the shell in that region. The 

 ligament end and most of the posterior parts are wanting, whilst the shell- 

 structure in the direction of the dorsal area is of immense thickness (nearly 

 35 mm.). The specimen is plano-convex, besides being much denuded of 

 sculpture characters, although appearing to correspond with what is present 

 on the smaller forms of this species even some radial costae can be obscurely 

 traced in places. It is interesting to note that De Lapparent 4 recognised a 

 large oyster in the Lutetian beds of the African Soudan (Tamaske, between 

 the Niger and the Tchad), resembling O. longirostris or O. aginensis, but 

 gave no important details of structure. It is possible, however, that that 

 form may represent the new species now described, although the evidence in 

 that direction is at present incomplete. As a matter of fact, Prof. H. 

 Douville' 5 has recently described an oyster, Crassostrea soudanensis, of large 



1 Tournouer : Bull. Soc. Geol. France, 1881, Ser. 3, Vol. 8, p. 294. 



2 Goldfuss : Petrefacta Germaniae, 1833, Vol. 2, pi. 77, figs. le, if, p. 15 ; see also Raulin and 

 Delbos : Bull. Soc. Ge"ol. France, 1855, Ser. 2, Vol. 12, part 2, p. 1157. 



3 Act. Soc. Linn. Bordeaux, 1914, Vol. 68, pi. 21, figs. 5-8, p. 190. 



4 Sur de Nouvelles trouvailles geologiques au Soudan: Compt. Rend. 1904, Vol. 139, p. 1189. 



5 L'Eocene au Soudan et au Senegal : Bull. Com. Etud. Hist. Sci. Afrique Occid. Fran$aise, 1920. 

 No. 2, p! 164, pi. 4, fig. 14. 



