30 MOLLUSCA FROM THE GREAT OOLITE. 



irregular width, with very narrow and waved interstitial sulcations, which are impressed 

 with densely arranged punctures ; the surface of the shell has likewise very fine transverse 

 striae. Striae of growth few and distant. 



This shell is moderately convex, the lateral and longitudinal diameters are nearly equal, 

 the umbones approximate and the auricles are small, the substance of the test is thin, and 

 the surface, except in young specimens, is usually distorted or crushed, so that it is nearly 

 impossible to obtain a large specimen which has not suffered in the process of fossilization. 

 The longitudinal elevations are so slight as scarcely to be considered costae, their surfaces 

 are smooth, shining, and so much flattened, as scarcely to impress a sensible convexity to the 

 touch. The numbers of the irregular costae vary from 40 to 48, they are equally distinct 

 upon every part of the shell, a feature which will always distinguish it from Lima gigantea, 

 and analogous species. Lima Iceviusculd, Deshayes, approximates to our species, but is 

 destitute of the dense punctations which mark the interstitial spaces ; the interstitial 

 sulcations are likewise evanescent upon the middle of the valves, which is not the case 

 with our shell. Lima aciculatd, Goldfuss, approaches this species in the character of its 

 markings, but it is much more flattened, aud the costae are regular and more numerous. 



This species is nearly as abundant as the Lima car dii for mis, which it everywhere 

 accompanies, but very frequently only in a crushed condition ; it is shorter than the 

 other and scarcely so convex. 



{d.) Lima bellula. Tab. Ill, fig. 9. 



Testa ovato-obliqud, laevigata; antice convexd, abrupte truncatd jaostice subcompressd, 

 rot /in da id ; auriculis parvis incequalibus; lunula magna excavatd; superficie striis radian- 

 tilus tenuibiis, nonnunquam obsoletis; striis anticis distinctis subdistantibus, posticis crebris 

 evanescentibus. 



Shell ovate, oblique, smooth; anterior side convex, abruptly truncated; posterior side 

 rather compressed, its margin rounded ; auricles small, unequal ; lunule large and deeply 

 excavated ; the surface is ornamented with very delicate radiating striations, which 

 anteriorly are distinct and rather distantly arranged, posteriorly they become much more 

 closely arranged and are usually indistinct. 



The general aspect of this species is shining and smooth, so that it is only upon close 

 examination that it is discovered to have radiating striations ; in young specimens these 

 are always more or less visible, but in specimens of advanced growth only a few traces 

 of the anterior striations remain. The concentric lines of growth are usually strongly 

 marked and efface the striations. 



With advance of growth some change is observable in the contour of the shell, it 

 becomes more transverse and nearly orbicular. 



Specimens from the Great Oolite of Lincolnshire do not attain to one third the 

 linear dimensions of others from the Inferior Oolite of the Minchinhampton district, but it 

 does not occur in the Great Oolite of Gloucestershire. 



