4 MOLLUSCA FROM THE GREAT OOLITE. 



Ostrea gregarea, Sow., var. Tab. I, fig. 2, 2a. 



Ostrea gregarea, Sow. Min. Con., t. Ill, f. 1 and 3, 1815. 



— — Gold/. Petref., t. 74, f. 2. 



— Bronn. Leth. Geog., p. 188, t. 18, f. 16, 1851. 



— palmetta, Sow. Min. Con., t. Ill, f. 2? 



Testa crassd, ellipticd, incurvatd costatd, valvd inferiore sub-carinatd, affixd, superiore 

 convexo-pland, costis numerosis, rugosis, subacutis radiantibus vel distichis. 



Shell oblong, irregular, curved, costated, with unequal convex valves, the beaks 

 slightly produced and incurved ; costse numerous, rugose, diverging. 



The specimens figured, are referred to the 0. gregarea, Sow., a social species which 

 occurs abundantly in the Coralline Oolite of Westbrook, Wiltshire, and near Weymouth 

 in Dorsetshire. The shells referred to this species in the Great Oolite are not generally 

 in good condition, and vary in form and plaiting ; some specimens presenting the 

 characters of 0. solitaria, Sow., others resembling the young state of 0. flabelloides, 

 Lamarck. 



Localities. Minchinhampton, and in the Oolite of Lincolnshire ; Stonesfield, Oxfordshire. 



Ostrea subrugulosa. Tab. I, fig. 6, 6a. 



1 Var. of Ostkea acuminata, Sow. 



Testa subtrigond, incurvd, concentrice rugosd; valvd inferiore convexd, sulcis furcatis 

 irregulariter radiantibus ornatd ; valvd superiore sub-pland ; apice obliquo sub-acuto. 



A somewhat trigonal incurved shell, concentrically imbricated or rugose, and with 

 irregular diverging small furrows on the convex valve ; the umbone incurved and obtuse ; 

 smaller valve flat and nearly smooth. 



A very common and characteristic species of the upper portions of the Great Oolite 

 in Northamptonshire and Lincolnshire, where it occurs in sandy and clayey beds, which 

 may probably represent the Forest Marble. It bears a general resemblance to the 

 0. acuminata, Sow., of which it may prove to be only a variety from difference of habitat? 

 but is distinguished by the more convex form and furrowed surface of the larger valve. 



Localities. In the Oolite of Kingsthorpe, Thrapston, Ouudle, &c, Northamptonshire; 

 and near Stamford, Lincolnshire. 



Ostrea Sowerbyi. Tab. I, fig. 3, 3a. 



Ostrea acuminata, Sow. Min. Con., t. 135, f. 3 not 2. 



Testa depressd, elongate!, curvatd rugosd, concentrice lamellosd ; valvd inferiore sub- 

 convexd, superiore plana ; umbone obtuso. 



A depressed elongated and slightly-curved shell, marked by concentric lamellae at 

 distant intervals. The umbones are nearly equal in size, broad, and obtuse. The larger 

 valve is rather convex ; the smaller valve flat, or sometimes a little concave. 



