BIVALVIA. 71 



Geological Positions and Localities. The specimen figured was obtained by 

 Mr. Whiteaves in the Great Oolite of Kirklington, Oxon. ; it has also occurred rarely in the 

 same formation at Minchinhampton Common, and in the Cornbrash of Islip, Oxon. 



CYPRINA BELLA, Lye. Tab. XL, figs. 15, 15 a. 



Testa ovato-orbiculari Icevigata, subdepressa, umbonibus mediocris, antero-medianis , 

 margine cardinali recto, subhorizontali, postice subangulata, lunula angusta vix depressa ; 

 superficic angulo postico obliquo instructo ; striis incrementi crebris, irregularibus. 



Shell transverse, ovately orbicular, smooth, rather depressed ; umbones of moderate 

 size, but little elevated, placed a little anterior to the middle of the valves and curved 

 forwards ; hinge margin straight, nearly horizontal, and slightly angulated posteriorly ; the 

 lunule is narrow, and but slightly impressed ; the exterior surface has an oblique angle, 

 posterior to which the surface is flattened ; the striations of growth, and delicate, numerous, 

 and irregular. 



The depressed form, posterior subhorizontal straight hinge border, and oblique 

 posterior angle, are the features that will serve to distinguish it from allied contemporaneous 

 forms. The numerous specimens placed at my disposal include examples from two to 

 nine lines in length, which measurements usually exceed the height by one fifth. 



Geological Position and Localities. The Forest Marble of Laycock and Pound Pill. 

 In the collection of W. Walton, Esq. 



CYPRINA DAVIDSONI, Lye. Tab. XXXVI, figs. 6, C a. 



Testa ovato-orbiculari crassa, convexa, obliqua, umbonibus obtusis submedianis antrorsum 

 inflectis, marginilus arcuatis curvatis, latere postico area subplanata, angula obtitso obliquo 

 interdum instructo, aut nullo ; lunula vix excavata, inconspicita, superficie striis concent-rids 

 irrcffularibus. 



Shell ovately orbicular, thick, convex, oblique, but varying much in the length and 

 obliquity ; umbones obtuse, submesial, directed forwards ; margins of the valves curved 

 elliptically and close fitting, lunule not conspicuous and scarcely excavated ; the posterior 

 side has a narrow, oblique, flattened space, sometimes separated from the other portion of 

 the surface by an obtuse angle ; in other instances there is no distinct angle ; the surface 

 has numerous irregular concentric and faintly marked plications. 



Dimensions of a large specimen of medium figure; length, 17 lines ; height, 15 lines ; 

 diameter through the valves, 11 lines. 



It is liable to be mistaken for Cyprina Lowcana, compared with which our shell is 



