144 CRETACEOUS LAMELLIBRANCHIA. 
consequently the character of the hmge and the adductor impression cannot be 
seen. A small oyster, as noted by Dr. 8. P. Woodward, is often found in the 
Chalk attached to echinoids, etc., and is similar in general appearance to Plicatula 
siyillina ; but it is easily distinguished by its triangular ligament-pit and clearly 
marked adductor impression, by the absence of ribs from the interior of the 
attached valve, and by the more porous structure of the shell. 
Types.—One of the types (Woodward’s fig. 1) from Grays is in the British 
Museum. The others, from the Upper Chalk of Norwich and Grays, I have not 
seen. 
Distribution—Upper Gault (zones x and xi) of Folkestone. Cambridge 
Greensand. Grey Chalk of Dover. Zones of R. Cuvieri, T. gracilis, and H. planus 
of Dover and the Sussex coast. Zone of M. cor-testudinariwm of Chatham, Dover, 
and the Sussex coast. Zone of M. cor-anguinum of Gravesend, the Thanet coast, 
Kingsgate Castle, St. Margaret’s, and the Sussex coast. Zone of Marsupites of the 
Thanet and Sussex coasts. Uintacrinus-band of Devizes Road (near Salisbury). 
Zone of A. quadratus of the Dorset and Sussex coasts. Zone of LB. mucronata of 
the Dorset coast, Hartford Bridge, ete. (near Norwich). 
