PLICATULA. 135 
1875. Purcaruta pLacunea, J. Phillips. Geol. Yorks., ed. 3, pt. 1, p. 244. 
1900. — — A. Wollemann. Die Biv. u. Gastrop. des deutsch. 
u. hollind. Kreide. (Abhandl. d. k. preuss. 
geo]. Land., n. F., pt. 31), p. 23. 
Deseription.—Shell very oblique, oval, projecting and pointed at the umbones ; 
length greater than height. Left valve flat or slightly concave; right valve 
convex. Both valves ornamented with strong angular ribs, usually eight to ten in 
number, bearing tubular overlapping spines; between these large ribs smaller ones 
are introduced, and bear spiny processes. Near the margin of the shell, in old 
individuals, the two sets of ribs may become of nearly equal size. The ribs are 
crossed by concentric, usually faintly marked lamelle, and at intervals by well- 
marked growth-lines. 
Measurements : 
(1) (2) (3) (4) 
Length . 36 27 25 19 mm. 
Height ! : 33 24. 2405 P40 ep 
(1—4) from Hythe. 
Affinities —This is distinguished from P. inflata, Sowerby, and P. Carteroniana, 
d’Orbigny, by greater development of spines and the presence of the smaller ribs. 
Distribution—Hythe Beds of Hythe, Lympne, St. Martha’s (Hast Shalford), 
Sevenoaks, and Maidstone. ? Ferruginous Sands of Shanklin. ? Speeton Clay. 
Recorded by Fitton (1847) from the Perna-bed of Atherfield.’ 
Pricaruta CarterontAna, d’Orbigny, 1847. Plate XXV, figs. 5a, b, 6a, b, 7—12. 
1847, PuicaruLa Carreroniana, A. d’Orbigny. Pal. France. Terr. Crét., vol. ii, 
p. 680, pl. eecexlii, figs. 5—7. 
1850. _ — d’ Orbigny. Prodr. de Pal., vol. ii, p. 83. 
1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 180. 
1871. _— Carteront, F. J. Pictet and G. Campiche. Foss. Terr. Crét, 
Ste. Croix (Mat¢r. Pal. Suisse, ser. 5), 
pp. 265, 271, pl. clxxxii, figs. 3, 4. 
1883. — — W. Keeping. Foss., etc., Neoc. Upware and Brick- 
hill, p. 110, pl. v, fig. 4. 
1896. — CarTERONIANA, A. Wollemann. Zeitschr. d. deutsch. geol. 
Gesellsch., vol. xlviii, p. 835. 
1 Measured obliquely from the umbo to the middle of the ventral margin. 
2 I have not been able to find the type or other specimens of Plicatula inwquidens, Sharpe, from 
the Lower Greensand of Faringdon, ‘ Quart. Journ. Geol. Soc.,’ vol. x (1853), p. 197, pl. vi, fig. 4. 
