PECTEN. 151 
ears much larger than usual, also a smaller apical angle, and straight antero- and 
postero-dorsal margins; the shell is rather high in proportion, and the ribs are 
numerous. Since all the Haldon specimens agree in these respects, and are readily 
distinguishable from those found elsewhere, they may be regarded as a local 
variety, and named P. orbicularis, var. haldonensis : this variety resembles the form 
from the Cenomanian of Bavaria figured by Séhle (1897). The forms found in 
the Upper Greensand of Warminster are rather larger than most of those in the 
Gault and Lower Cretaceous, and often have numerous ribs. 
5, Cenomanian.—Small forms, with a variable number of ribs, occur commonly 
in the Chalk Marl, and rarely also a very large variety, sometimes reaching 76 mm. 
in height (Text-fig. 1). In the H. subglobosus zone the average size is rather 
Fia. 1.—Pecten (Syncyclonema) orbicularis, Sow. Chalk Marl, Folkestone. Woodwardian Museum. 
Natural size. 
larger than in Gault and Lower Cretaceous, but no forms as large as those in the 
Upper Greensand mentioned above have been seen. The number of ribs is 
variable. 
Lypes.—The type, from the Upper Greensand of Devizes, appears to have been 
lost, and the same is the case with the types of P. laiinosus from the Chalk Marl 
of Hamsey and Stoneham. 
Distribution.—Folkestone Beds of Folkestone. Lower Greensand of Upware. 
Spilsby Sandstone of Donnington and Spilsby. Claxby Ironstone of Benniworth 
Haven. ‘Tealby Limestone (zone of LB. brunsvicensis) of North Willingham and 
Claxby. Speeton Series (same zone) of Speeton (fide Lamplugh). 
Also recorded in the Geological Survey Memoirs from the Perna-bed of Ather- 
