PROTOCAPDIA. 195 



inequilateral, length and height nearly equal. Antero-dorsal margin nearly 

 straight. Anterior margin convex, curving rapidly to join the ventral margin, 

 which is moderately or slightly convex. Posterior margin truncated, forming 

 angles with the ventral and postero-dorsal margins. Umbones large, curved 

 forwards, with a sharp carina extending in a curve to the postero-ventral angle 

 and limiting the flattened, steeply-sloping posterior area, the dorsal portion of 

 which is concave. Shell depressed in front of the umbones. 



Ornamentation : Sides of shell nearly smooth except for numerous, very small, 

 concentric ribs which are separated by flat interspaces. The posterior area is 

 covered, except near the postero-dorsal margin, by 12 strong radial ribs. 



Measurements : 



(1) (2) (3) 



Length . 80 . 70 . 46 mm. 



Height . 78 . 79 . 40 „ 



(1 — 3) Crackers, Atherfield. 



Affinities. — This species resembles P. Forbesi (Pictet and Renevier), 1 from the 

 Lower Aptian of Ste. Croix, but the umbones are less prominent, and the ribs on 

 the posterior area are less numerous. 



It is also similar to P. impressa (Deshayes), 2 but is distinguished by the 

 smaller curvature of the ventral margin, the greater flattening of the sides of the 

 shell, and the more considerable curvature of the umbones. 



Distribution. — Lower Greensand (Crackers) of Atherfield. 3 



Peotocaedia SPHiEEOiDEA (Forbes), 1845. Plate XXXI, figs. 2, 3. 



1845. Caudium sph^koidiuki, E. Forbes. Quart. Journ. Geol. Soc, vol. i, 



p. 243. pi. ii, fig. 8. 

 1850. A. d'OrUgny. Prodr. de Pal., vol. ii, p. 79. 



1852. neckerianum, F. J. Pictet and W. Roux. Moll. Foss. Gres 



verts de Geneve, pp. 424, 

 425, pi. xxx, fig. 3. 

 sph^koideum, Pictet and Roux. Ibid., p. 546. 

 1854. J. Morris. Cat. Brit. Foss., ed. 2, p. 193. 



1 'Foss. Terr. Aptien ' ('Mater. Pal. Suisse,' ser 1, 1856), p. 79, pi. viii, fig. 4; Pictet and 

 Campiche, 'Terr. Cret. Ste. Croix (Mater. Pal. Suisse, ser. 4, 1866), p. 261. 



2 D'Orbigny, 'Pal. Franc. Terr. Cret.,' vol. iii (1844), p, 20, pi. ccxl ; Pictet and Cainpiche, 

 op. cit., p. 249. 



3 Some specimens of Protocardia from the Lower Greensand of Atherfield were referred by Forbes 

 to Cardium peregrinorsum, d'Orbigny, but that identification was doubted by Pictet and Campicbe. 

 The specimens at present available are insufficient for exact determination. See Forbes, ' Quart. 

 Journ. Geol. Soc.,' vol. i (1845), p. 243. 



