SCIIIZODUS CARBONARIUS. 223 



surface of the valves is regularly convex, the greatest convexity being near the 

 upper part of the shell ; the dorsal slope is compressed and hollowed, the postero- 

 superior angle being somewhat alate. 



Interior. — The anterior adductor scar is very shallow and inconspicuous; 

 the posterior large and irregular, elongate from above downwards, and situated 

 along the whole of the dorsal margin just within the edge of the valve. The 

 pallial line is entire and remote from the margin. The hinge has not yet been 

 exposed. 



.Exterior. — Though the shells are nearly all casts, traces of fine regular con- 

 centric lines of growth are to be seen preserved near the margins. 



Dimensions.— Fig. 9, PI. XVII, measures — 



Antero-posteriorly . . . .42 mm. 



Dorso-ventrally . . . .39 mm. 



From side to side . . . .26 mm. 



Localities. — England : the Penuystone Ironstone, Coalbrookdale, and Rosser 

 Vein, Cwm Bryn ddu, South Wales Coal-measures. 



Observations. — This species, as far as my present knowledge goes, seems to be 

 confined to a single horizon in the Coalbrookdale and South Wales Coal-fields. 

 M'Coy described some shells from the coal shales intercalated in the limestones 

 near Berwick-on-Tweed under the name Myophoria carbonaria (' Brit. Pal. Foss.,' 

 p. 495), referring them to the Venus ? carbonaria of Sowerby. These shells I now 

 refer to S. Pentlandicus, Rhind, sp., after the examination of several specimens 

 collected by myself from the shale above the Cooper's-eye Coal, Scremerston, and 

 a fine series in the Woodwardian Museum, Cambridge, on which M'Coy probably 

 founded his description. 



Portlock was in error in referring his shell to Venus ? carbonaria, Sowerby ; a 

 comparison of the types at once shows that the former is a much flatter triangular 

 shell, which I am of opinion belongs to the genus Protoschizodus, de Koninck. 

 Portlock's shell is refigured on PI. XVII, fig. 11, of this Monograph. 



A series of shells from Coalbrookdale, among which is the type, which I 

 reproduce (PI. XVI, fig. 7) by the kindness of the authorities, is preserved in the 

 British Museum (Nat. Hist.), South Kensington. These specimens formed part of 

 the collection made by Sir J. Prestwich when preparing his paper on the Coal- 

 brookdale Coal-field. 



The curious fauna of the Pennystone Ironstone of this coal-field has a much 

 lower facies than generally obtains in the Coal-measures, and it is important to 

 note its similarity with that in the Rosser Vein and at the base of the South 

 Wales Coal-field. 



8. carbonarius differs very markedly in shape from any of the other species of 

 the genus ; unfortunately the shells mostly occur in the form of internal casts, and 



