PLICATULA. 135 



1875. Plicattjla placunea, J. Phillies. Geol. Yorks., ed. 3, pt. 1, p. 244. 

 1900. — — A. Wollemann. Die Biv. u. Gastrop. des deutsch. 



u. holliind. Kreide. (Abhandl. d. k. preuss. 



geol. Land., n. F., pt. 31), p. 23. 



Description.— Shell very oblique, oval, projecting and pointed at the umbones ; 

 length greater tlian 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 lamellas, and at intervals by well- 

 marked growth-lines. 



Measurements : 













(1) (2) 



(3) 



(4) 





Length . 



36 27 



25 



19 1 



nn 



Height 1 



33 24 



(1—4) from Hythe. 



24-5 



20 



J5 



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 (East Shalford), 

 Sevenoaks, and Maidstone. ? Ferruginous Sands of Shanklin. ? Speeton Clay. 

 Recorded by Fitton (1847) from the Perna-hed of Atherfield.^ 



Plicatula Caeteroniana, d'Orbigny, 1847. Plate XXV, figs. 5 a, b, 6 a, b, 7 — 12. 



1847. Plicatula Carteeoniana, A. d'Orhigny. Pal. Fran9. Terr. Crt't., vol. iii, 



p. 680, pi. ccccxlii, figs. 5 — 7. 

 1850. — — d'Orbigny. Prodr. de Pal., vol. ii, p. 83. 



1854. — — /. Morris. Cat. Brit. Foss., ed. 2, p. 180. 



1871. — Carteboni, F. J. Pictei and G. Campiche. Foss. Terr. Cret. 



Ste. Croix (Mater. Pal. Suisse, ser. 5), 

 pp. 265, 271, pi. clxxxiii, figs. 3, 4. 

 1883. — — W. Keeping. Foss., etc., Neoc. Upware and Brick- 



hill, p. 110, pi. V, fig. 4. 

 1896. — Carteeoniana, A. Wollemann. Zeitschr. d. deutsch. geol. 



Gesellsch., vol. xlviii, p. 835. 



1 Measured obliquely from the umbo to the middle of the ventral margin. 



" I have not been able to find the type or other specimens of Plicatula insequidens, Sharpe, from 

 the Lower Greensand of Faringdon, ' Quart. Journ. Geol. Soc.,' vol. x (1853), p. 197, pi. vi, fig. 4. 



