PLICATULA. 143 
testudinariwm of Dover and the Sussex coast. Zone of M. cor-anguinum of the 
Thanet coast, the North Foreland, St. Margaret’s, and the Sussex coast. Uintacrinus 
band of Kingsgate. Marsupites zone of the Sussex and Thanet coasts. Zone of 
B. mucronata of Clarendon, near Salisbury. 
PLICATULA SIGILLINA, Woodward, 1864. Plate XXVI, figs. 19—22. 
2? 1852. Sponpyius picnoromus, A. Buvignier. Statist. géol., ete., de la Meuse, 
Atlas, p. 25, pl. xix, figs. 16, 17. 
1864. Puicarua starnyina, 8S. P. Woodward. Geol. Mag., vol. i, p. 112, pl. v, 
figs. 1—5. 
Description.—Shell small, semi-oval or semicircular in outline, a little oblique. 
Hinge margin long. Right valve attached by nearly the whole of its surface ; 
interior with slightly raised radial ribs, somewhat irregular, becoming more 
numerous at the sharp raised margin; beyond this margin is a broad smooth 
sloping border bounded by a raised edge, outside which are, in some cases, radial 
ribs. Left valve slightiy convex, ornamented with well-marked concentric lamelle. 
Measurements : 
® 2 8 ® © © @ © @ ~ «@o) 
Lencth 4 lo 8s 65 11. 16 9) 17 18) 2mm: 
Height’. 12 15 17 6 10 12 9 516" diGe sols: 5, 
(1—3) M. cor-testudinarium zone, Chatham. 
(4—6) M. cor-anguinum zone, Gravesend. 
(7—10) B. mucronata zone, Hartford Bridge, Norwich. 
Affinities—The form from the Gault of Clermont and Les Islettes (Argonne, 
Meuse), described by Buvignier as Spondylus dichotomus, is probably identical with 
this species; it is especially like examples of P. sigillina from the Cambridge 
Greensand and the Gault of Folkestone. 
P. sigillina differs from the other Cretaceous Plicatulz here described in bemg 
attached by almost the entire surface of the right valve, and in the absence of 
radial ribs or folds on the left valve ; in these respects it resembles the completely 
fixed forms of the recent species P. philippinarum, Hanley. 
Remarls.—This species occurs attached to Hchinocorys, Inoceramus, Belemnitella, 
and other fossils. The fixed valve is common in the Norwich Chalk and the 
Cambridge Greensand. The left valve is much less frequently found than the 
right, and at present appears to be known only from the Upper Chalk and the 
H. planus zone. The inner layer of the shell has undoubtedly disappeared, and 
! Measured obliquely. 
