BIVALVIA. 7 



Placunopsis socialis. Tab. I, fig. 9, 9a. 



Testa parvd ovato-orbiculari, valvis valde inmqualihus et irregularihus, lineis radiantibus 

 subtillissimis confertis ; plicis concentricis paucis irregularibus. 



Shell small, ovately orbicular, with the valves very unequal and irregular ; the 

 umbones are marginal but very depressed, and scarcely distinguishable ; the surface is 

 covered with extremely fine densely arranged radiating lines, which are commonly visible 

 under a magnifier upon the convex valve, and very rarely in the flat valve ; the concentric 

 plications are few, strongly marked and irregular. 



This httle shell is usually coloured with tints varying from lake to indigo and brown ; 

 it occurs throughout all the shelly beds of the Great Oolite in the Minchinhampton 

 district ; and towards the middle of the series in the soft shelly Oolite or oven stone, it is 

 peculiarly abundant and gregareous, the largest specimens having a diameter of about 

 7 lines ; although it does not exhibit any marks of having been attached or compressed, 

 the figure of the valves is even more irregular than in P. Jurensis. 



Localities. Minchinhampton and Bisley Commons. 



Placunopsis ornatus. Tab. I, fig. 11, 11«. 



Testa parvd, ovato-orbiculari subpland, fragili, umbonibus sub-marginalibus depressis, 

 costulis radiantibus numerosis equalibus et regularibus, aliisque interstitialibus tenuissimis, 

 costulis spinisjistidosis, numerosis, depressis ornatis. 



Shell small, ovately orbicular, transverse, compressed, irregular, very thin ; umbones 

 sub-marginal, depressed, radiating costse elevated, rounded, numerous, equal and regular, 

 with interstitial and very fine striae ; the costse are ornamented with numerous depressed 

 fistulous spines. 



The radiating costse are elevated and undulated, and the numerous depressed fistulous 

 spines which ornament them render it a pretty object under the magnifier ; the character 

 of the surface altogether is very similar to that of Ostrea spondyloides, (Schloth, Goldfuss, 

 t. 72, fig. 5,) but that species pertains to the Muschelkalk. The other valve has not been 

 recognised. 



Locality. Minchinhampton Common. 



Placunopsis radians. Tab. I, fig. 10. 



Testa parvd sub-orbiculatd, umbone parvd, depresso, sub-marginali, lined cardinis 

 subrectd ; costulis radiantibus rotundis distantibus et Jlstulosis, interstitialibus lavigatis; 

 plicis concentricis distantibus. 



Shell small, sub-orbicular; umbo small, depressed, sub-marginal, hinge line nearly 

 straight ; radiating costse rounded, elevated, rather irregular, distant, with fistulous 

 plications upon their surfaces ; the interstitial spaces are smooth ; the concentric pHcations 

 are few and distant ; the general convexity of the shell is moderate, but the convex valve 

 is unknown : not unfrequently near to the border a second series of costse commence, but 



