EXOGYRA. 419 



1872. OsTREA (Esogtra) digitata, H. B. Geinifz. Das Elbthalgeb. in Sachseu 



(Palteontograpliica, vol. 

 x.\-, pt. 1), p. 184, pi. xl, 

 fig. 14. 



1882. Exooyra digitata, G. Seyuenza. Atti R. Accad. Lincei, ser. 3, CI. Sci. 



Fis. Math., vol. xii, p. 180. 



Descript ill It. —^heW inequilateral, with rounded outline; height and lengtli 

 often nearly e([ual. 



Left valve moderate]}', s(Mnetinies con.sideral)ly convex. Umbo spiral, curved 

 considerably backwards ; the attached snrface small, and posterior to tlie umbo. A 

 carina, sometimes sharp, sometimes roimded, extends in a cnrve from the nmbo 

 towards the postero-veutral extremity, and becomes less distinct on the later part 

 of the valve ; behind the nmbo the valve is concave or flattened. A few prominent, 

 widely separated radial folds are present ; some start from the carina, others 

 begin later, and the ventral part of the carina sometimes becomes replaced by a 

 fold. The dorsal folds are curved. On the folds strong spine-like projections are 

 often developed, and form projections at the margin of the valve. Fine growth- 

 lines occur, and bend over the folds. Right valve nearly flat. 



Affinities. — 0. vnJtur, Coquand,' resembles this species in its strong folds and 

 spines, but the left valve is more inflated and the carina less distinct. E. digifafa 

 shows considerable resemblance to some forms of E. cornu ariiiis (Xilsson)' from the 

 Senonian, in which is included E. laciniafa (Xilsson). 



Except for the strong radial folds E. digitota resembles some of the less convex 

 forms of E. sinnafit, from which it may have been derived. 



Tijpe. — The types, from the Upper Greensand (zone of Pecten asper) near 

 Sidmouth, cannot be found. 



DistribufioH. — Upper Gi-eensand (zone of Fecfen asper) of Beer, Weston 

 (Devon), Evershot, and White Notlie (Dorset). 



ExoGVEA siGMOiDE.v, Reuss, 1844. Plate LXI, fig. 12. 



1844. EsoGYRA SIOMOIDEA, A. E. lieiiss. Geoguost. Skizz. Biihtuen, vol. ii, 



p. 180. 

 1846. — — A. E. Eeiiss. Die Versteiu. derbohiu. Kreidefoniiat.. 



pt. 2, p. 44, pi. xxvii, figs. 1 — 4. 



' ' Men. Ostrea, Terr. Cr^t.* (1869), p. 118, pi. xxxix, figs. 1 — 4. Rhynchostreon nilhir, Bavk-, 

 ' Exp'ical. Carte gcol. France,' vol. iv (1878), Atlas, pl.cxli. 



= Nilsson, ' Petrifie. Suecana' (1827), p. 28, pi. viii, fig. 1. Griepenkerl, ' Palaeont. Abhandl.,' v..I. 

 iv (1889), p. 35, pis. V, vi, vii, figs. 6, 7, Heniiig, 'Revis. Lamellibr. i Nilssou's Petrifie. Suecana' 

 (18;t7), p. 21. Chama laciniata, Nilsson, o^). cit., p. 28, pi. viii, fig, 2. 



