270 CARBONIFEROUS LAMELLIBRANCHIATA. 



be obtained. The Middle Coal and Ironstone series consists almost exclusively 

 of fresh-water beds, there being only one thin bed containing marine fossils, and 

 these even are confined to those species which could stand a large mixture of 

 fresh water. 



Caediomobphia paeva, Hind, sp. nov. Plate XIX, figs. 17 — 21. 



Specific Characters. — Shell small, globosely triangular, the transverse and 

 dorso-ventral diameters almost equal, inequivalve. 



The anterior end is short, its upper border, descending rapidly downwards, 

 makes it very short from above downwards in the extreme front ; its upper 

 portion being excavated below, the overhanging umbo is concave. The border is 

 almost elliptically curved, and passes into the ventral edge without a break. The 

 latter border is very slightly convex, and forms the greatest transverse diameter 

 of the shell. The posterior border is subtruncate, making an obscure obtuse 

 angle with the hinge-line ; but below it is gradually rounded off into the inferior 

 border. 



The hinge-line is arcuate, the umbones comparatively large, much raised, 

 prosogyrous, and contiguous, though the points are far apart. 



The valves are convexly swollen from above downwards, and from before 

 backwards, the greatest degree of convexity being about the middle point of the 

 valve. There is a very slight amount of compression at the postero-superior 

 angle. 



Interior. — The muscle-scars, pallial line, and hinge have not yet been exposed. 

 Exterior. — The surface is ornamented with very fine concentric strias, visible 

 only with the microscope; but over the umbones these lines become obsolete. 

 Dimensions. — Fig. 21, PI. XIX, measures — 



Antero-posteriorly . . . .11 mm. 



Dorso-ventrally . . . .10 mm. 



Elevation of valve . . . .5 mm. 



Localities. — England : the Redesdale Ironstone, Redesdale, Northumberland. 

 Scotland : Upper Limestone series of Orchard and Clonbeith, Kilwinning; Lower 

 Limestone series of Waterland, near Dunlop ; Shale between the Lower Lime- 

 stones, Gateside, Beith. 



Observations. — I have erected this species on a fairly numerous suite of speci- 

 mens from the Redesdale Ironstone, collected by Mr. John Dunn, of Redesdale, 

 and myself. I have referred the shell to the genus Cardiomovpha on external 

 characters only, as at present I have not been able to discover any specimens 



