360 CRETACEOUS LAMELLIBRANCHIA. 



0. Leymerii, from which it appears to differ in its somewhat smaller ribs. The 

 forms with a small surface of attachment resemble 0. baissunensis, Bolim, 1 but have 

 coarser and less regular ribs. 0. lagena, Seeley (fig. 141), is a form of 0. cunabula 

 with a very large attached surface, and consequently a less convex left valve. 



Types. — From the Cambridge Greensand (indigenous). The type of 0. lagena 

 is in the Sedgwick Museum, Cambridge ; the type of 0. cunabula cannot be found, 

 but other specimens named by Seeley are in the Sedgwick Museum. 



Distribution. — Cambridge Greensand (base of Chalk Marl), Cambridge. Chalk 

 Marl of Burwell. 



Ostrea Walkeki, Keeping, 1883. Plate LV, figs. 1 — 3. 



1883. Ostrea Walkeki, W. Keeping. Foss., etc., Neoc. Upware and Brickhill, 



p. 103, pi. iv, fig. 4. 



Remarks. — This form is similar to 0. Gerniaiiti and 0. Leymerii; the chief 

 difference mentioned by Keeping — the inequality of the valves — is not constant, 

 and is determined by the size of the attached surface. Harbort regards 0. Walkeri 

 as a synonym of 0. Germaini, Coquand, 2 but the material available is hardly 

 sufficient for definite determination. Some of the specimens with a large attached 

 surface resemble 0. Osmana, Wollemann. 8 



Type. — In the Sedgwick Museum, Cambridge. 



Distribution. — Lower Greensand of Upware. 



Ostrea vesicularis, Laniard-, 1806. Plate LV, figs. 4 — 0. Text-figures. 143 — 182. 



1779. B. Faujas-St.-Fond. Hist, nat. Mte. St. Pierre de Maestricht, 



pi. xxii, fig. 4; pi. xxv, figs. 2, 5. 

 1806. Ostrea vesicularis, Lamarck. Ann. Mus. Hist, nat., vol. viii, p. 160, and 



vol. xiv (1809), p. 375, pi. xxii, fig. 3. 

 — deltoidea, LainarcJc. Ibid., p. 160 ; vol. xiv (1809), p. 374, pi. 



xxi, fig. 3 (non deltoidea, Sowerbv). 

 1816. — , W. Smith. Strata identif. Organised Fossils, p. 7, pi. iii, figs. 5 — 7. 



1819. — vesicularis, Lamarck. Animaux sans Vert., vol. vi, p. 219. 



1820. — convexa, T. Say. Amer. Journ. Sci., vol. ii, p. 42. 



1 ' Zeitschr. d. deutsch. geol. Gesellsch.,' vol. Ii (1899), p. 466, pi. xxix, figs. 1 — 3. 



2 Coquand, 'Mon. Ostrea, Terr. Cre't.' (1869), p. 191, pi. lxvi, figs. 14—16. Pictet and Campiche, 

 'Terr. Crct. Ste. Croix' ('Mater. Pal. Suisse,' ser. 5, 1871), p. 295, pi. elxxxix, figs. 1—6. Wolle- 

 mann, ' Bivalv u. Gastrop. deutsch. u. holliiiidisch. Neocoms ' (1900), p. 18, pi. i, fig. 4. Harbort, 

 'Fauna Schaumburg-Lippe'schen Kreidemulde ' (1905), p. 28. 



3 Op. cit. (1900), p. 19, pi. i, fig. 5, pi. ii, fig. 1. 



