12 MOLLUSCA FROM THE GREAT OOLITE. 



Testa obliqud, ovato-orbiculari, plano-convexd, sub-eequivalvi, reticulatd, lineis confertis 

 concentricis et radiantibus arcuatim diveryentibus, hinc inde furcatis ; auriculis incequalibus 

 reticulatis. 



Shell oblique, ovately orbicular, moderately convex, equivalve, radiating lines narrow, 

 closely arranged, irregular, curving outwards, the interstitial spaces densely punctated or 

 reticulated, occasionally bifurcated; concentric lines irregular; auricles unequal and 

 reticulated. 



There does not seem to be any sufficient or constant character which will enable us to 

 separate this species from the Pecten annulatus of the Mineral Conchology and of 

 Goldfuss; both have occasionally a certain degree of obliquity; the radiating lines of both 

 are reticulated and bifurcated, becoming almost evanescent in the ultimate stage of 

 growth; in the latter condition, the concentric elevated lines become constant, are much 

 more prominent than the radiating lines, and do not furnish any peculiar or characteristic 

 feature, we are therefore inclined to reunite the two species, and regard the annulated form 

 to be merely a variety of the present one. Next to the Pecten vagans, this ranks as the 

 most abundant Pecten of the Great Oolite, its vertical range is likewise remarkable, as it 

 is found throughout the rocks of the entire Oolitic system ; but attains its greatest deve- 

 lopment of size in the Coralline Oolite of Malton. 



Localities. Wherever the Great Oolite is fossiliferous. 



PECTEN ANNULATUS, Sow. Tab. I, fig. 13. 



? Var. of PECTEN LENS. 

 PECTEN ANNULATUS, Sow. Min. Con., t. 542, f. 1, 1826. 



Goldfuss. Petref., t. 91, f. 2. 

 OBSCDRUS, Sow. Min. Con., t. 205, f. 1.? 



Testa ovato-orbiculari, sub-aquivalvi, convexo-pland, striis radiantibus subtillissimis, 

 ineequalibus arcuatim divergentibus, lineis aut lamellis concentricis distantibus interruptis ; 

 auriculis incequalibus striatis. 



Shell ovately orbicular, nearly equivalve, rather depressed, radiating striations very 

 fine, unequal, densely arranged, and diverging, the striations are broken and interrupted 

 by prominent concentric lamellae, which are rather distantly arranged ; auricles unequal, 

 striated. 



The apicial portion of the shell is destitute of the concentric lamellae, which commence 

 abruptly and continue to the lower border of the shell. It occurs commonly in the 

 Cornbrash, Forest Marble, and in the upper portion of the Great Oolite ; but is not found 

 in the shelly beds of the Michinhampton district. 



Localities. Near Cirencester, and at Sapperton Tunnel, Gloucestershire ; in the upper 

 beds of the Great Oolite, at Blisworth, Kingsthorpe, and other places in Northamptonshire 

 and Lincolnshire ; it occurs also in the Stonesfield Slate. 



