PROTOCARDIA. 195 



inequilateral, luugtli 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, \evy small, 



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



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



MeiiHuremeuts : 



(1) (^) (3) 



Length . 80 . 7G . 46 mm. 



Height . 78 . 71) . 40 „ 



(1 — 3) Crackers, Atherfield. 



Acuities. — This species resembles J'. Forhesi (Pictet and Renevier),^ 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. iiu.jjre^sa (Deshayes),~ 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. 



Distribatioii. — Lower Greensand (Crackers) of Atherfield.* 



PiiOTorAuniA spn.KROiOEA {Forbes), 1815. Plate XXXI, tigs. 2, S. 



1845. Caedium sPHasRoiDiUM, E. Forbes. Quart. Jouru. Guol. Soc, vol. i, 



\i. 243. pi. ii, fig. 8. 

 1850. — — A. iVOrhujiiij. Prodr. de Pal., vol. ii, p. 79. 



1852. — NECKEKiANUM, F. J. Fictiit uiid \V. Roiix. MoU. Foss. Ores 



verts de Geneve, pp. 424, 

 425, pi. XXX, fig. 3. 

 — — si'UJiuoiDKUM, Fidft and Roax. 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 aud 

 Caiiipiuhc, 'Terr. Crct. Ste. Croix (Matur. Pal. Suisse, ser. 4, 18(50), p. 261. 



^ D'Orliiguy, -Pal. Fraut. Terr. Cret.,' vol. iii (1841.), p, 20. pi. ccxl ; Pictet aud Caiupiche, 

 op. cit., p. 249. 



* Some specimeus of Protocardia t'rojn the Lower Greeusand of Atherfield were referred by Forbes 

 to Cardium peregrinorsum, d'Orbiguy, but that ideutificatiou was doubted by Pictet and Campiche. 

 The speciuicus at present available arc iusufficieut for exact deteruiinatiou. See Forbes, * Quart. 

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



