CARBONIFEROUS LAMELLIBRANCMIATA. 



reg'ular concentric thin ribs, which he regards as of diagnostic value in the 

 identification of the species, sutficiently well indicated. 



CrjNOPiSTHA PAiivuLA, (Ic Konwcl', 1885. Plate L, figs. 18 — 20. 



CLiNOPisxnA PARA'TJLA, de Konitick, 1885. Ann. Mus. Eoy. Hist. Nat. Belg., 



vol. xi, p. 124, pi. xiii, figs. 28, 29 ; pi. xxiii, figs. 22—25. 



Specific CJiaracfcrs. — Shell small, very inequilateral, bean-shaped, gibbose, 

 close all round ; upper and lower margins almost parallel. The anterior end 

 comprises nearly the whole of the valve, and is somewhat expanded and gibbose, 

 but is rapidly compressed into the margin, which is rounded, the curvature being 

 greater at the antero-inferior than at the antero-superior angle, which is somewhat 

 blunted. The inferior margin is slightly convex, but is often sinuous about its 

 centre. The posterior end is very short, compressed, depressed, and bluntly 

 truncate. The superior margin is elevated and straight anterior to the umbo, but 

 depressed posteriorly. The umbones are small, flattened, pointed, not raised, 

 twisted backwards, and excavated posteriorly by the escutcheon. The valves are 

 regularly convex, more so from above downwards than from before backwards. 



Interior. — The anterior adductor muscle-scar is shallow, obliquely placed, 

 pear-shaped, remote from the margin ; the posterior scar is deeper and more 

 rounded, occupying nearly the whole of the posterior end* Hinge edentulous. 

 On each side of the hinge-line is a groove in which are to be seen obscure linear, 

 elongate ridges, passing from before backwards. The inner surface of the shell 

 is marked by obscure concentric grooves and ridges, crossed by very fine, almost 

 microscopical radiating lines, more apparent over the front of the valve. Pallial 

 line entire. 



Exterior. — The shell is ornamented with fine concentric folds and strice of 

 growth. Apparently no radiating striee. Shell thin. 



Dimensions. — PI. L, fig. 18, measures — 



Antero-posteriorly . . . .16 mm. 



Dorso-ventrally . . , .10 mm. 



From side to side . . . .7 mm. 



Locality. — England : the Fourlaws Limestone, the Coomb, Redesdale, 

 Northumberland. 



Observations. — Mr. J. Dunn has obtained several specimens of this little shell 

 from the above-named locality. De Koninck's specimens seem to have attained 

 only to about half the size of the British examples. 



