70 MOLLUSCA FROM THE GREAT OOLITE. 



horizontali producto, postice subrostrato, attenuate ; margins cardinali subrecto, oblique 

 declivi ; costis concentricis crebris imbricatis ; margine inferno integro. 



Shell thick, convex, transversely elongated, umbones large mesial ; anterior side pro- 

 duced subhorizontal ; posterior side more attenuated, slightly rostrated ; hinge border 

 nearly straight, elongated, and sloping obliquely; concentric costse densely arranged, 

 regular imbricated ; inner margins of the valves smooth. 



A very rare shell readily distinguished from other contemporaneous species by the 

 finer and more densely arranged costse. 



Height 16 lines; length 25 lines; diameter through both the valves 13 lines. 



Locality. Minchinhampton Common, where it occurs in the bed of coarse planking. 



CORBIS LAJOYEI, Far. cingenda. Tab. VII, fig. 11. 



Testa ovato-rotundatd concentrice costatd ; costis magnis subdistantibus prominulis 

 lamelliformibus ; latere antico brevi, marginibus rotundis. 



Shell ovately rounded, convex, concentrically costated ; costae rather distant, regular, 

 prominent, lamellar, anterior side short, margins rounded. 



The figure is less elongated than in the preceding species, more especially the anterior 

 side ; the costse are much more distantly arranged. 



Height, one inch ; length, an inch and a quarter ; rare. 



Locality. Minchinhampton Common, in the bed of coarse planking. 



CORBIS ASPERA. Tab. VII, fig. 13, 13. 



CORBIS ASPERA, Lycett. Ann. Nat. Hist., Dec. 1850, pi. 11, f. 7. 



Testa ovato-elonffatd, convexd, umbonibus subacutis prominulis, costis concentricis 

 subacutis regnlaribm distantibus. 



Shell ovately elongated, convex, umbones prominent, mesial, rather acute ; concentric 

 costse regular, distinctly arranged, and rather acute. 



Compared with C. cingenda, the figure is more elongated, the umbones more pointed, 

 and the costas are more elevated and distantly arranged. 



Height, 8 lines, length, 1 1 lines ; but larger specimens occur in the Inferior Oolite. 



Localities. Minchinhampton Common, in the Great Oolite ; the vicinity of Nailsworth, 

 in the Inferior Oolite. 



- 

 Sub-Genus, SPH^RA, Sow. 



Shell thick, subaequilateral, equivalve, globose, umbones large, contiguous, directed 

 forwards, lunule small, but slightly excavated, ligament external, surface smooth, or 

 impressed only with the folds of growth. Hinge, massive, with two cardinal teeth in the 

 right valve, these are thick and united beneath the umbo ; the posterior one is prominent, 

 and placed transversely to the hinge plate, the anterior one is oblique and elongated 



