94 MOLLUSCA FROM THE GREATO OLITE. 



Geological position and localities. T. aaniniformis occurs in the Inferior Oolite of 

 Yorkshire, and in the Great Oolite of Ponton, Lincolnshire, and of Minchinhampton, in 

 the shelly beds. 



Tancredia plan ata. Tab. XIII, fig. 10a, b. 



Testa ovatd, planatd ; umbonibus submedianis parvis acuminatis ; antice compressd; 

 postice plano-convexd ; margine postico oblique-curvato ; antico recto oblique declivi ; basi 

 curvatd. 



Shell ovate, flattened ; umbones nearly mesial, small, and acute ; anterior side com- 

 pressed, its extremity rounded ; posterior side rather more convex ; the posterior margin 

 has an oblique curvature ; the anterior margin is straight, and slopes obliquely ; the base is 

 curved elliptically. 



A delicate, smooth, and flattened shell, the anterior extremity of which is much less 

 acuminated, and the posterior less truncated than is usual in this genus. It is moderately 

 abundant in the shelly beds of the formation, and varies considerably both in its outline 

 and degree of convexity. 



Height, 9 lines ; length, 13 lines. 



Localities. Minchinhampton and Bisley Commons. 



Tancredia angtjlata, Lycett. Tab. XIII, fig. 9a, b. 



Tancredia angtjlata,. 'Lycett. Journ. Geol. Soc, 1853, vol. 9, p. 341, pi. 14, f. 5. 



Testa ovato-trigond ; umbonibus elatis, medianis, acutis ; latere antico compresso ; postico 

 angulum obliquum formante ; margine cardinali brevi, recto horizontali ; basi curvatd. 



Shell ovately subtrigonal ; umbones elevated, mesial, acute ; anterior side compressed ; 

 posterior side with an oblique angle separating a flattened posterior portion ; ligamental 

 margin short, horizontal ; basal margin with a considerable curvature. 



This species, which is smaller than T. curtansata, is distinguished from that form by 

 the flattened and angulated posterior side, and by the more erect and acute umbones; and. 

 from the Inferior Oolite T. donaciformis, by the more erect, acute umbones, and more 

 lengthened form ; the basal margin has also a more considerable curvature. 



Height, 9 lines ; length, 14 lines. 



Geological position and localities. Ponton, Lincolnshire, and Minchinhampton ; at 

 both places in the Great Oolite. 



Corbis. Sub-genus — Corbicella . 



Testa inornatd, ovato-elongatd, subcompressd ; wnbtmibm plerumque antemcdianis 

 depressis, contiguis ; margine superiore elomgato, subrecto, obliquo ; ligamento cxterno 



