CARDIUM. 201 



P. delicatula, Stoliczka, 1 and P. pondicheriense (d'Orbigny), 2 are allied to 

 P. Hillana. 



P. biseriata (Conrad), 3 from Syria, possesses coarse concentric ribs, and is 

 regarded by Blanckenhorn as a variety of P. Hillana. 



Remarks. — Examples of this species are common at Blackdown, but probably on 

 account of the uniformity of the conditions under which they lived, do not show 

 any very striking variations. 



There are some differences in the proportion of length and height ; usually the 

 former exceeds the latter slightly, but occasionally the two are equal. The outline 

 of the shell is sometimes oval, but more usually subquadrate. The radial ribs vary 

 in number from 10 to 15, and sometimes the area with these ribs is continued for a 

 short distance in front of the posterior slope. 



The number of concentric ribs in 10 mm. (measured between 34 mm. and 

 44 mm. from the umbo) varies from 15 to 19. 



Type. — From Blackdown, in the British Museum. 



Distribution. — Upper Greensand (zone of Schloenbachia rostrata) of Blackdown, 

 Haldon, Whitecliff (South Devon), Peak Hill near Sidmouth, Devizes, and 

 Ventnor. Cenomanian of Dunscombe. Recorded by Jukes-Browne from the 

 Chloritic Marl of the Isle of Wight. 



Genus — Oaedium, Linnaeus. 



(' Syst. Nat.,' ed. 10, 1758, p. 678 ; ed. 12, 1766, p. 1121.) 



Cardium Ibbetsoni, Forbes, 1845. Plate XXXII, figs. 7 — 10. 



1845. Cardium Ibbetsoni, E. Forbes. Quart. Journ. G-eol. Soc, vol. i, p. 243, 



pi. ii, fig. 9. 

 1854. — /. Morris. Cat. Brit. Foss., ed. 2, p. 192. 



1856. F. J. Pictet and E. Benevier. Foss. Terr. Aptien 



(Mater. Pal. Suisse, ser. 1), p. 78, 

 pi. ix, figs. 1, 2. 

 1866. F. J. Pictet and G. Campiche. Terr. Cret. Ste. Croix 



(Mater. Pal. Suisse, ser. 4), 

 p. 262. 

 1871. — (L^vicardipm), F. Stoliczka. Palseont. Iudica, Cret. 



Fauna S. India, vol. iii, p. 213. 



1 ' Palaeont. Indica, Cret. Fauna S. Iudia,' vol. iii (1871), p. 220, pi. xiii, fig. 8. 



3 Stoliczka, ibid., p. 220, pi. xii, figs. 4—7. 



3 ' Official Report U. S. Exped. Dead Sea, etc.,' by W. F. Lynch (1852), p. 216, pi. vi, figs. 38, 39 

 (non 40); R. B. Newton, ' Geol. Mag.,' (1898), p. 400, pi. xv, fig. 11. P. Hillana var. typica, 

 M. Blanckenhorn, ' Beitr. zur Geol. Syriens : Kreidesyst. in Mittel u. Nord-Syriens ' (1890), p. 89. 



