BIVALVIA. 29 



LIMA SEMICIRCULARIS, Goldf. Tab. Ill, fig. 3, 3 a. 



LIMA SEMICIKCCLAKIS, Goldfuss. Petref., t. 101, f. 6. 

 PLAGIOSTOMA SEMICIHCULAKIS, Quenstedt. Wurtt., p. 477. 



Testa convexd, oblique semicirculari, antice truncatd, costulis crebris aqualibus convexis, 

 canalibus interstitialibus anffustioribus concentrice confertim striatis, lunuld plano-concavd. 



Shell moderately convex, obliquely semicircular, anterior side straight, truncated, ribs 

 closely arranged, very numerous, convex, the interstitial spaces more narrow, and 

 impressed with very delicate striae ; lunule flattened, or slightly excavated, umbones 

 approximated, pointed, auricles small, hinge border straight. 



This species has some general resemblance to young specimens of Lima cardiformis, 

 but may be distinguished from it by the more elongated, depressed, and less oblique form, 

 and more especially by the more pointed and depressed umbones, the costse also, contrary 

 to that species, are often slightly undulated, and the lines of growth form two or three 

 prominent rounded elevations. The average size is about an inch in length. It is 

 moderately abundant in the shelly beds. 



Locality. The whole of the Minchinhampton district. 



(c.) LIMA OVALIS, Sow. Tab. Ill, fig. 5, 5 a. 



PLAGIOSTOMA OVALIS, Sow. Min. Con., t. 114, f. 3, 1815. 

 LIMA OVALIS, Goldf. Petref., t. 101, f. 4. 



Testa convexd oblique ovatd, antice truncatd, costulis convexis aqualibus crebris, sulcis 

 i nterstitialibus transversim lineatis, lunuld concavd. 



Shell ovate, moderately convex, umbones pointed, auricles very small, anterior border 

 nearly straight, the side steep and rounded, posterior border curved nearly in a semicircle ; 

 costa3 convex, but very densely arranged, equal and marked with extremely delicate 

 transverse striae, the interstitial spaces are very narrow and punctated. 



The costae are equal and waved, but so fine as scarcely to be traced without the aid of 

 a magnifier, the auricles in size are reduced almost to nothing. The general dimensions 

 nearly accord with Lima semicircularis, but it is more convex and oblique, the anterior side 

 being more steep and rounded. 



Locality. It is not very abundant, but occurs throughout the shelly beds of the 

 formation over the Minchinhampton district, and likewise at Ancliff. 



(d.) LIMA IMPRESSA. Tab. Ill, fig. 8, 8 a. 



Testa convexd obliqud, ovato-orbiculari, antice truncatd, costulis depressis, irregularibus 

 sulcis angustis interstitialibus undulatis, punctis crebris impressis, et striis transversalibus 

 tenuissimis notatis. Striis incrementi paucis distantibus. 



Shell convex oblique, ovately-orbicular, anterior side truncated, costae depressed, of 



