144 CRETACEOUS LAMELLIBRANCHIA. 



consequently the character of the hinge and the adductor impression cannot be 

 seeii. A small oyster, as noted by Dr. S. P. Woodward, is often found in the 

 Chalk attached to echinoids, etc., and is similar in general appearance to Plicatula 

 sujillina; 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. 



Tjjpes. — 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 B. Cuvieri, T. gracilis, and H. planus 

 of Dover and the Sussex coast. Zone of M. cur-testudinarium 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-bdindi of Devizes Road (near Salisbury). 

 Zane of A. quadratus of the Dorset and Sussex coasts. Zone of B. mucronata of 

 the Dorset coast, Hartford Bridge, etc. (near Norwich). 



