BIVALVIA. 63 



Geological Positions and Localities. This well-marked little Corbula has been kindly 

 forwarded by J. F. Whiteaves, Esq., from the Great Oolite of Kirklington, Oxon.; also by 

 W. Walton, Esq., from the Forest Marble of Laycock, Wilts. 



CORBULA INVOLUTA, Munst. Tab. XXXVII, figs. 4, 4 a. 



CORBULA. INVOLUTA, Gold/. Pet., t. 151, fig. 14. 

 CYPKINA D'Orb. Prodrome, i, p. 2/8, No. 309. 



Testa crassa, parva, perinflata ; concentrice subtillissime striata ; umbonibus magnis 

 obtitsis, submedianis ; latere antico rotunda, postico rostrato, obtuse carinato et attenuate. 



Shell small, thick, greatly inflated, with very delicate, concentric striations ; umbones 

 large, obtuse, submesial ; anterior side short, rounded, posterior side attenuated, rostrated, 

 its margin concave, and forming at its lower extremity an acute angle ; the posterior slope 

 has delicate, transverse striations; it is somewhat flattened, very narrow, and is only 

 obscurely separated from the dorsal portion of the shell by an obtuse angle ; the lower 

 border is nearly straight. 



Length, one third greater than the height and the diameter through both the valves. 



The foregoing description will serve to distinguish it from a small, thick, but less in- 

 flated species, abundant in the Great Oolite of Minchinhampton, and which was formerly 

 regarded by me as C. involuta of Munster, and figured under that title in Part II, Tab. VI, 

 of the ' Great Oolite Monograph/ and described in Part II, p. 97 ; it had previously 

 been figured and described by Professor Buckman, in Sir R. Murchison's ' Geology of 

 Cheltenham,' 2nd ed., p. 97, pi. 3, fig. 4, under the title of Corbula striata ; but as that 

 name had already been appropriated by Lamarck for an Eocene Corbula, it becomes 

 necessary to change it to C. Buckmatii, under which name it is refigured, Tab. XXXVII, 

 fig. 8, thrice magnified. 



Geological Position and Locality. The Great Oolite of Kirklington, Oxon. ; collected 

 by J. F. Whiteaves, Esq. 



CORBULA ISLIPENSIS, Lye. Tab. XXXVII, fig. 7. 



Testa parva, infiata, umbonibus medianis, magnis, crectis, latere anteriore rotunda, 

 posteriors brevi, abrupte truncato, angulo obliquo instritcto ; valvis longitudinaliter striatis, 

 striis magnis regularibus, lineis angustis separatis ; lunula excavata ; basi subrecto. 



Shell small, inflated, but subquadrate or cuculaeform ; umbones large, mesial, erect ; 

 anterior side rounded, its lunule excavated; posterior side short, abruptly truncated, with 

 an oblique and subacute angle separating a posterior smooth and slightly concave 

 area ; the lower border is nearly straight ; the dorsal surface has large, regular, 



