CYPRICARDELLA PARALLELA. 349 



deep lunule, compressed, with a regularly rounded border. The inferior margin 

 is regularly and gently convex. The posterior margin is subtruncate, slightly 

 convex, the postero-inferior angle regularly rounded, the postero-superior a well- 

 marked slightly obtuse angle. The hinge-line is arched, produced, and depressed 

 posteriorly. The umbones are small, incurved and twisted forwards, pointed, 

 contiguous, slightly raised above the hinge-line, and placed at the junction of the 

 anterior and middle thirds of the valve. Passing obliquely downwards and back- 

 wards from the umbo to the postero-inferior angle is an obscure ridge which 

 separates the compressed and flattened dorsal slope from the rest of the valve, 

 which is regularly but gently curved, the greatest convexity of the valves being 

 subumbonal. A strong ridge passes backwards from the umbo to the postero- 

 superior angle, separating the escutcheon from the dorsal slope. The escutcheon 

 is large and elongate, and trench-like. 



Inferior. — No details of the interior have been observed. 



Exterior. — The surface is ornamented with regular, close, concentric, fine 

 ridges and sulci, which are continued over the dorsal slope, and terminate in the 

 hinge-line. Shell comparatively thick. 



Dimensions. — Fig. 3, PI. XXXIX, from South-west Yorkshire, measures — 

 Antero-posteriorly . . . .17 mm. 



Dorso-ventrally . . . .14 mm. 



From side to side . . . .9 mm. 



Localities. — The Carboniferous Limestone of Hill Stebden, Yorkshire, and 

 Pilsbury, Derbyshire. 



Observations. — Type specimen of Phillips's Venus parallela is preserved in the 

 Gilbertson Collection of the Natural History Museum, South Kensington, and I am 

 permitted to refigure it by the kind permission of Dr. Henry Woodward, fig. 1, 

 PI. XXXIX. It is a much smaller specimen than some of those 1 figure, but is 

 fairly perfect. De Koninck somewhat doubtfully referred a specimen from the 

 Limestone of Vise to this species (op. supra cit.) ; and de Ryckholt also adopted it, 

 but undoubtedly described as new, shells of this same species which varied slightly 

 in shape from his conception of the type. De Koninck in his later work adopted 

 several of de Ryckholt's species, but I consider that these are founded on insuffi- 

 cient evidence, the minor differences of size and strength of the external ornament 

 not being of specific value. 



G. concentrica approaches nearer to G. parallela than any other species of the 

 genus, but the hinge-line is much straighter and more produced posteriorly, and 

 much less compressed, the concentric ridges are much fewer, larger, and further 

 apart, and the shells less convex. 



Phillips gives the locality for his shell as Bollaud. I have not yet been able 

 to obtain any of his species in that district, though the majority of those 



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