EXOGYRA. 419 



1872. Ostrea (Exogyra) digitata, if. B. Geinitz. Das Elbthalgeb. in Sachseu 



(Palseontograph ca, vol. 

 xx, pt. 1), p. 184, pi. xl, 

 fig. 14. 



1882. Exogyra digitata, G. Seguenza. Atti R. Accad. Lincei, ser. 3, CI. Sci. 



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



Description. — Shell inequilateral, with rounded outline ; height and length 

 often nearly equal. 



Left valve moderately, sometimes considerably convex. Umbo spiral, curved 

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

 carina, sometimes sharp, sometimes rounded, extends in a curve from the umbo 

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

 of the valve ; behind the umbo 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. vultur, Coquand, 1 resembles this species in its strong folds and 

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

 shows considerable resemblance to some forms of E. cornu arietis (Nilsson) 2 from the 

 Senonian, in which is included E. laciniata (Nilsson). 



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

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



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

 Sidmouth, cannot be found. 



Distribution. — Upper Greensand (zone of Pecten asper) of Beer, Weston 

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



Exogyra sigmoidea, Reuss, 1844. Plate LXI, fig. 12. 



1844. Exogyra sigmoidea, A. E. Reuss. Greoguost. Skizz. Bohmen, vol. ii, 



p. 180. 

 1846. — — A. E. Reuss. Die Verstein. derbohm. Kreideformat., 



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



1 ' Mon. Ostrea, Terr. Cret.' (1869), p. 118, pi. xxxix, figs. 1—4. Ehynchostreon vultur, Bayle, 

 ' Explicat. Carte geol. France,' vol. iv (1878), Atlas, pi. cxli. 



2 Nilsson, • Petrific. Suecana ' (1827), p. 28, pi. viii, fig. 1. Griepenkeil, ' Pakeont, Abliandl.,' vol. 

 iv (1889), p. 35, pis. v, vi, vii, figs. 6, 7 Hennig, 'Revis. Lamellibr. i Nilsson's Petrific. Suecana' 

 (1897), p. 21. Chama laciniata, Nilsson, op. cit., p. 28, pi. viii, fig. 2. 



