OSTREA. 391 



Woodward, from the zone of Belemnitella mucronata of Norwich, is in the Norwich 

 Museum (Plate LIX, fig-. 14). 



Distribution. — Chalk Marl (zone of Schloenbachia varians) of Burham and 

 Dover. 1 



Totternhoe Stone (zone of Holaster subglobosus) of Burwell. 



Zone of Rhynchonella Cuvieri of White Nothe (Dorset), Peter's Pit (Burham) 

 and Dover. 



Zone of TerebratuJina lata of Branscombe, Warnford (Hants) and Beachy 

 Head. 



Zone of Micraster cor-anguinum of Quidhampton, New Brompton, and Grays. 



Zone of Marsupites testud ina rvu is of Devizes Road (Salisbury), Taplow and West 

 Wickham. Uintacrimts band of the Thanet coast. 



Zone of Actinocamax quadratus of East and West Harnham, West Meon, Mottis- 

 font, Soberton and Winterbourne (Berks). 



Zone of Belemnitella mucronata of Alderbury, Clarendon and Norwich. 



Ostrea Boucheroni, Ooquand, 1859. Plate LX, figs. 1 — 15. 



1859. Ostrea Boucheroni, H. Coquand. Bull. Soc. gcol. de France, ser. 2, vol. 



xvi, p. 1007. 

 1862. — tevesthensis, Coquand. Gcol. Pal. reg. sud. Province Constantine, 



p. 227, pi. xix, figs. 7—13. 

 1869. — Boucheroni, Coquand. Mon. Ostrea, Terr. Cret., p. 85, pi. xxxi, 



figs. 1 — 3; pi. xxxvii, figs. 1 — 16; pi. 

 xxxviii, fig. 20. 

 1890-1. — A. Peron. Descript. Brack, etc., Terr. Cret. Tunisie, 



p. 142. 

 1898. G. Midler. Mollusk. Unterseu. v. Braunschweig u. 



Ilsede (Abhandl. d. k. preuss. geol. 

 Landesanst., n.f., 25), p. 11, pi. iii, 

 figs. 5—9. 



Description. — Shell variable in form, usually considerably higher than long, 

 with the anterior and posterior margins generally diverging gradually from the 

 umbo. Often the shell is more or less nearly symmetrical, but may be irregular, 

 and with the ventral part expanded. 



Left valve very convex, with the anterior and posterior parts sloping rapidly from 

 the flank to the margin. The flank is flattened or moderately convex. Umbonal 

 region usually narrow and pointed. The attached surface is at the umbo and is 

 usually rather small but sometimes large ; when large the height of the shell may 

 be relatively small, and the form of the left valve more or less semi-cylindrical. In 



1 Specimens of Ostrea found in the Upper Greensand of Haldon resemble closely 0. incurva. 



