EDMONDIA PENTONENSIS. 313 



have served as an attachment for muscle or ligament; it is not roughened or 

 punctate, but is the representative probably of the winged process described by 

 King as present in Edmondia sulcata (' Mon. Permian Fossils,' p. 164, pi. xx, 

 figs. 3 and 4). 



The shape and contour of a great many of the specimens obtained at Redes- 

 dale are misleading. Very frequently the cast has not been completely filled, and 

 the contours of the anterior and posterior extremities are often made to appear 

 as if truncated and obtuse. This condition can be easily recognised by tracing 

 the concentric markings which are present both on the exterior and anterior, 

 which will be found to terminate abruptly on the anterior and posterior margins, 

 instead of curving round, in each case, to end in the upper border of the valve. 

 Occasionally good impressions of the exterior can be obtained from a bed of 

 shelly calcareous ironstone which occurs in the series of the Redesdale Ironstone 

 Measures. 



Edmondia Pentonensis, sp. nov. Plate XXXV, figs. 12 — 16. 



Specific Characters. — Shell of medium size, transversely oblong-oval, elongate, 

 compressed, upper and lower margins sub-parallel, very inequilateral. The 

 anterior end is short, compressed, but deep from above downwards, its border 

 regularly and almost semicircularly curved. The inferior margin is long, very 

 slightly convex ; the posterior border is bluntly rounded below and curved above, 

 but the curvature of its upper portion is the arc of a much larger circle than that 

 of the lower part. The hinge-line is much shorter than the greatest length of the 

 shell, and almost straight, slightly elevated posteriorly. The umbones are small, 

 incurved, and twisted forwards, contiguous, raised above the anterior end of the 

 shell, but not elevated above the hinge-line, and situated in the anterior fifth of 

 the shell. 



The valves are regularly but very slightly curved from above downwards and 

 before backwards. The posterior end is somewhat expanded, being deeper than 

 the anterior in a dorso- ventral diameter. There is a narrow elongate groove for 

 the external ligament, parallel to and just above the hinge-line. 



Interior. — The arrangement of the muscle-scars has not been seen. The hinge 

 is edentulous, and has a long narrow ridge projecting outwards into the umbonal 

 cavity. 



Exterior. — The surface is covered with numerous fine liues of growth, arranged 

 concentrically, with several shallow, broad, concentric sulci, more pronounced near 

 the lower margin, and here and there a line much more apparent than the others. 

 Shell very thin. 



