BIVALVIA. 51 



Shell trapeziform convex, the surface with irregular concentric rugose plications, 

 anterior side short, convex, its margin rounded, posterior side with an oblique obtuse 

 angle, the side posterior to the angle compressed and truncated ; umbones large, incurved, 

 and almost touching each other ; area lanceolate, of moderate size, with 5 or 6 striae. 



This species has some resemblance to Cucullcea oblonga, Phillips, but it is less 

 elongated, the umbones are more compressed, and it is destitute of all radiating lines ; 

 the more oblique form, compressed umbones, and longer posterior side, will distinguish it 

 from Cucullcea cucullata, when the surface markings of that species are not distinguishable. 



Height, 16 lines; length, 21 lines; diameter through both the valves, 14 lines. 



Localities. Minchinhampton and Bisley Commons, where it occurs in all the shelly 

 beds. 



Cucullcea cucullata, Goldfuss. Tab. V, fig. 5. 



Cucull.ea cucullata, Goldfuss. Petref., p. 148, t. 123, f. 7, 1840. 



Testa ovato-rhomboided, ventricosd, umbonibus antemedianis approximates, latere postico 

 compresso-declivi, concavo, carinato tcevi ; lineis concentricis confertis et radiantibus 

 subtillissimis. ( Goldfuss . ) 



Shell ovately rhomboidal, ventricose, umbones placed anterior to the middle of the 

 shell, oblique, and somewhat separated ; posterior side with an oblique obtuse carina, 

 posterior to which is a flattened or slightly concave surface ; the inferior margin is curved ; 

 the lines both radiating and concentric are closely arranged, very fine, but irregular and 

 unequal, the part posterior to the carina or angle being destitute of lines ; the plications 

 of growth are faintly marked, few, and distant. 



The finely reticulated surface is usually most distinct in young specimens, those of 

 more advanced growth being nearly smooth. It occurs throughout the shelly beds of the 

 Great Oolite, but is not abundant. It likewise occurs in the middle division of the Inferior 

 Oolite at Leckhampton, and near to Nailsworth in Gloucestershire. 



Locality. Minchinhampton Common. 



Nucula, Lam., 1801. 



Gen. Char. Shell transverse, inequilateral, ovately oblong ; hinge linear, separated 

 in the middle by a fossa or oblique channel ; teeth numerous, elevated, narrow, or frequently 

 comb-like ; umbones contiguous, curved posteriorly ; ligament partly internal, inserted in 

 the central fossa or canal. 



Nucula variabilis, Sow. Tab. V, fig. 13, \2>a. 



Nucula variabilis, Sow. Min. Con., t. 4".">, f. 2, 1824. 



— — Phil. Geol. York., vol. i, t. 9, f. 11, 1835. 



NucuLi subglobosa, Roemer. Verst. Oolith., t. 6, f. 7, 1836. 



