388 CARBONIFEROUS LAMELLIBRANCHIATA. 



Sanguinolites tkansversus, Etheridjje, 1888. Ibid., p. 290. 

 — UNDATus, Etheridge, 1888. Ibid., p. 290. 



Specific Characters. — Shell above the medium size, transversely elongate, 

 oblong, curved from before backwards, compressed, very inequilateral. The 

 anterior end is exceedingly short, compressed, somewhat narrower from above 

 downwards than the rest of the valve. Its border is curved elliptically in the 

 3^ounger stages of growth, but more obtusely rounded in older examples. The 

 inferior border is very long, and slightly convex in the whole of its extent. The 

 posterior border is almost straight obliquely, truncate from above, downwards, 

 and backwards. The postero-inferior angle is bluntly rounded ; but the postero- 

 superior has a well-marked obtuse angle. The hinge-line is long, curved by its 

 shght elevation towards the posterior end, so as to be concave along its free 

 border. The umbones are very small, narrow, compressed, pointed, and directed 

 forwards, not raised above the hinge-line, and situated in the anterior sixth of the 

 valve. The upper edge of the valve is formed by a w^cll-marked elongated ridge, 

 erect, formed by the sudden bending of the valve on itself, and this separates the 

 elongate, narrow escutcheon from the rest of the valve. Passing downwards and 

 backwards, obliquely towards the postero-inferior angle is an almost obsolete 

 fold, soon lost on the surface of the valve ; it separates the compressed dorsal 

 slope from the rest of the valve. The valve is only slightly convex from 

 before backwards, but more so from above downwards. There is an obscure 

 compression about the middle of the valve. The lunule is narrow and ob- 

 scure. 



Interior. — The anterior adductor scar is deep and round, marked off from the 

 rest of the valve by a ridge; it is placed near the antero-superior angle and 

 surmounted by an accessory muscle-scar, which is smaller, and lies between it 

 and the umbo. The posterior adductor scar is large, shallow, and obscure. 

 Pallial line entire. 



The hinge-line is unknown in its anterior part, but posteriorly it is edentulous, 

 and possesses an elongate rolled edge placed at right angles to the valve, and 

 separated from it by a groove. Below and parallel to the hinge-line is an 

 elongate process of shell which leaves a groove in casts ; this becomes broader 

 and deeper as it passes backwards, till it becomes obsolete at some little distance 

 from the posterior border. 



The interior of the valve is marked with concentric grooves and folds, which 

 are obsolete in front and in the hollow of the dorsal slope. 



Exterior. — The surface is covered with fine strise and rugee of growth, grouped 

 into concentric folds and rounded ridges, which all follow the contour of the 

 valve. Close, and less well-marked in front, the ridges separate as they pass over 



