PECTEN. 155 
occur on the same geological horizons, and since each shows some variation in the 
proportions of length and height, there seems no reason to regard them as more 
than varieties of one species. 
The concentric grooves are generally more widely separated in the specimens 
from the Speeton Clay than in those which come from the Claxby Ironstone. 
This species has usually been known on the Continent as P. crassttesta, owing, 
no doubt, to the fact that the type of P. cinctus came from the Drift, and its true 
horizon was for some time thought to be Middle Jurassic; also to the fact of its 
Fig. 2.—Pecten (Camptonectes) cinctus, Sow. Claxby Ironstone, Claxby. Woodwardian Museum, 
The higher and shorter form of the species. x j. 
being the form with a higher shell, which is rather less common than the other 
variety. 
T'ype.—In the British Museum; from the Drift—probably derived from the 
Claxby Ironstone. 
Distribution.—Claxby Tronstone (zone of Bel. lateralis) of Claxby, North 
Willingham, Tealby, Donnington. Tealby Limestone (zone of Bel. brunsvicensis) 
of Claxby. Speeton Series (zone of Bel. jaculum, D1, D 4, D 5) of Speeton. 
