68 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 
Common, collected by E. Witchell, Esq. A specimen has also been brought under my 
notice by S. P. Woodward, Esq., but its locality is uncertain. 
TancreDIA GiBBosa, Zyc. Tab. XXXV, fig. 7. Tab. XXXVI, fig. 11. 
TANCREDA cipBosa, Lyc, Cott, Hills Handb., p. 121, pl. 7, fig. 4. 
Testa subtrigona, tumidula, umbonibus medianis acutis, latere antico attenuato, postice 
tumido subangulato ; dorso levigato, plicis incrementt, paucis irregularibus. 
Shell subtrigonal, tumid ; umbones elevated, pointed, and placed a little anterior to the 
middle of the valves; the anterior side is rather attenuated and pointed at the lower 
extremity ; the posterior side slopes obliquely downwards, it is somewhat tumid, and has an 
oblique angle slightly defined; the surface is smooth, but with a few plications of growth 
towards the lower border. 
Height, 10 lines ; length, 13 lines; diameter through both the valves, 6 lines. 
It is distinguished from other Great Oolite species by the combination of a trigonal 
outline with a tumid figure. 
Geological Position and Locality. It occurs rarely in the Great Oolite shelly 
weatherstones of Minchinhampton Common, and the Forest Marble of Farleigh, 
Somerset. 
TANCREDIA MACTREHOIDES, Whiteaves, MSS, Tab. XXXV, fig. 4. 
Testa ovato trigona, convexa, umbonibus submedianis elevatis, incurvis ; margine antico 
hreviore, leviter excavato, margine postico oblique declivi, angulo oblique leviter instructo, 
basi elliptico curvato. 
Shell ovately trigonal, convex, with a few concentric plications; umbones antero- 
mesial, elevated, and incurved; anterior border the shorter, slightly concave ; the extremity 
pointed; posterior hinge-border sloping obliquely ; there is also a posterior oblique angle 
faintly marked. 
Zancredia gibbosa, Lyc., approximates to this species, but is more convex, with a more 
elevated and rounded posterior slope. 7. aziniformis, Phil., from the Inferior Oolite of 
Yorkshire, is more flattened, with more pointed umbones and acute posterior angle, 
Height two thirds of the length. 
Geological Position and Locality. The Great Oolite of Stonesfield, Oxon., where it 
appears to be rare ; collected by J. F. Whiteaves, Esq. 
Tancrepia sIMILIs, Whiteaves, MSS. Tab. XXXYV, fig. 9. 
Testa ovato elongata, umbonibus antemedianis, latere antico attenuato, breviore ; postico 
convexo, angulo obtuso obliquo ; basi elliptica curvata, 
