360 CRETACEOUS LAMELLIBRANCHIA. 



0. Lpijmen!, from which it appears to differ in its somewhat smaller ril)s. The 

 forms with a small surface of attachment resemble O.bdis.^unensis, Bohm/ but have 

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

 with a very large attached surface, and consequenth- a less convex left Aalve. 



Tiipes. — From the Cambridge Greensand (indigenous). The type of 0. hiijriiii 

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

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



Dititrihiition. — Cambridge Greensand (base of Chalk ]\Iarl), Camljridge. Chalk 

 Marl of Burwell. 



OsTREA W.\i.Ki:i;i, Krrpiinj, 1883. Plate LY, figs. 1—3. 



1883. OsTREA Walkeki, W. Keepiiaj. Foss., etc., Neoc. Upware aud Bric-khill, 



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



Reiiuirlcs. — This fonn is similar to 0. Germaini and 0. Li'i/iiicrii; the chief 

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

 and is determined b}' the size of the attached surface. Harbort regards 0. ]\'(illien 

 as a synonym of 0. Germaini, Coquand,- but the material available is hai-dly 

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

 surface resemble 0. Oxmana, AVoliemann.'' 



TijiH\ — In the Sedgwick Museum, Cambridge, 



Distribiilion. — Lower Greensand of Upware. 



OsTiiEA VKsirri,Ai(is, Lauunrh, 180(1. Plate LV, figs. 4—0. Text-figures. 14:5—182. 



1779. — B. Faujas-St.-Foitd. Hist. imt. Mto. St. Pierre de Maestricht, 



jil. xxii, fig. 4; jil. XXV, figs. 2, 5. 

 18Ut). OsTREA VESicuLARis, Lamars}:. Ann. Mus. Hist, uat., vol. viii, p. IGO, aud 



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

 — — DELTOlDEA, Laiiiarch. Ibid., p. 160; vol. xiv (1809), p. 374, pi. 



xxi, fig. 3 (uou deJtoidea, Sowerbv). 

 1816. — ■ , ir. SinitJi. Strata ideiitif. Organised Fossils, p. 7, pi. iii, figs. 5 — 7. 



1819. — VESICULARIS, Lamarck. Aiiimaux sans Vert., vol. vi, p. 2Ut. 



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



1 ' Zeitschr. d. deutsch. geol. Gesellsch.,' vol. li (1899), p. 46(5, pi. xxix, figs. 1—3. 



- Coquand, ' Mon. Ostrea, Terr. Cn't.' (1869), p. 191, pi. Ixvi, figs. 14—16. Pictet and Canipiclie, 

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

 mauu, ' Bivalv ii. Gastrop. deutsoli. u. hoUiindisch. Neocoms ' (1900), ji. 18, pi. i, fig. 4. Harbort, 

 'Fauna Sehaumburg-Lippe'scheu Kreidemulde ' (1905), p. 28. 



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



