OSTREA. 375 



DescripfioiL—Lah valve usually tliick, very convex, grypheate, more or less 

 oval, height usually considerably greater than the length ; slightly or moderately 

 ine(|uilateral, sometimes with a rounded ridge extending from the umbo to the 

 postero-ventral extremity. Posterior part often convex and separated from the 

 reiuainder of the valve l)y a furrow. Umbo sharp, prominent, more or le.ss 

 incurved, and usually witli a small posterior curvature; surface of attachment 

 generally small. Area and ligament-pit high, straight or with a small backward 

 curvatui-e. Adductor impression oval or rounded. Right valve thin, concave. 

 Surface of both valves smooth, except for growth-lines. 



Abilities. — This species is closely allied to 0. vesicularix, but the umbo is more 

 pointed, usually less incurved and with a smaller attached surface; the area is 

 higher, and usually the height of the shell is relatively greater in proportion to its 

 length. Most of these differences are probably to be accounted for by the small 

 size of the attached surface. 



Tiipe. — From the Upper Greensand of AVarininster, in the British Museum. 



DUtvibntiiin. — Upper Greensand : common in the zone of Scldoenhachia rostrata 

 of Ventnor, Warminster, Dinton and Potterne; rare in the zone of Fcxti'ii nxpar 

 of Ventnor, Warminster, and Ballard Down (Swanage). Chloritic Marl of 

 Coinptou Bay, Isle of Wight. 



OsTKKA CAXALKULATA {Soivcrbi/), 181:5. Plate LVI, figs. 2-10. 



1813. Chama canaliculata, /. Soiiyrhi/. Miu. Conch., vol. i, p. 68, \>\. xxvi, tig. 1 



(uou Oslrea canaliculata, Sowerb}'.) 

 1821. OsTREA CANALICULATA, M. J. L. Defiance. Diet. Sci. luit., vol. xxii, ]>. 26. 

 18-27. OsTBEA LATERALIS, 5". Nilssoti. Petrific. Suecaua, p. 29, pi. vii, tigs. 7 — 10. 



— Chama conica, Nilsson. Ibid., p. 28, pi. viii, tig. 4. 



1829. Gryph.«a canaliculata, J. de C. Sowerhij. Miu. Couch., vol. vi, p. 218. 



— Exogyra undata, Sowerhy. Ibid., vol. vi, p. 220, pi. dcv, figs. 5 — 7. 

 1833. OsTREA lateralis, a. GohlJ'uxx. Petref. Genu., vol. ii, p. 24, \A. Ixxxii, 



%. 1. 

 y 1834. GRVPH.tiA VOMER, S . G . Mortoii. Synopsis Organic Remains Cret. U. States, 



p. 54, j>l. ix, fig. 5. 

 1837. OsTREA LATERALIS, \V. HIkI ii(jei\ Letliaea Sueeica, p. 4ti, pi. xiii, fig. 1. 



— Ami'uiuonte undata, G. G. Punch. Polens Pahiout., ]>. 39. 



1842. Exogyra parvula, A. Leijmerie. Ml'iu. Soc. gc'ol. de France, ser. 2, vol. v, 



p. 17, pi. xii, figs. 8, 9. 

 1845-6. OsTREA lateralis. If. B. Geinitz. Grundriss d. Versteiu., p. 480, pi. xx, 



fig. 22. 



1846. Exogyra laterali.s, A. E. Rcukk. Die Versteiu. der biihui. Kreideforuiat., 



pt. 2, p. 42, pi. xxvii, figs. 38 — 47. 



1847. Ostrea canaliculata, .1. il'Orhiijuij. I'al. Franc. Terr. Crct., vol. iii, 



]<. 709, pi. cccclxxi, figs. 4—8. 



