GIRTY, NEW CARBONIFEROUS FOSSILS 321 



with any proi3riety be included immediately with the typical specimens 

 or with the variety gracile. jSTevertheless, it is difficult to establish any 

 line between them, partly, no doubt, because of imperfect material, whose 

 real characters must be more or less estimated, but partly also because 

 of intermediate specimens. The specimen selected as the tj-pe has both 

 valves of nearly equal convexity. It has a subpentagonal shape with a 

 distinct, though ill-defined, sinus in the ventral valve. Another example 

 is still more rotund. 



Dielasma planiconvexum sp. nov. 



Shape broadly subovate or spatulate, length but slightly in excess of the 

 width. Outline regularly rounded. Ventral valve moderately convex longi- 

 tudinally and transversely. Dorsal valve nearly flat, slightly convex in a 

 transverse direction. Fold and sinus practically absent, although the anterior 

 portion of the ventral valve is flattened out and slightly bent upward, causing 

 an almost imperceptible deflection of the margin. 



This species is described from an imperfect specimen. 



Ambocoelia planiconvexa var. fayettevillensis var. nov. 



Shell small, subcircular and transverse. Width probably always slightly 

 in excess of the length and in some specimens considerably so. Cardinal 

 angles rounded ; hinge much shorter than the width below. Greatest width 

 occurs about the mid-length or a little posterior to it. 



Ventral valve only moderately convex for the genus and rapidly expanding. 

 Beak rather small, not strongly elevated, inclined backward, or incurved. 

 The area is not very distinctly defined, and it is intersected by a moderately 

 broad delthyrium, much higher than broad, which occupies from one fourth to 

 one third of its width at the cardinal line. 



Dorsal valve gently convex to subplanate, with a fairly distinct though nar- 

 row sinus developed near the front of mature and half-grown specimens. 



The shells of this genus vary so little that the greater portion of a 

 detailed description of the present form would apply to most of its 

 species. 



Spiriferina subelliptica var. fayettevillensis var. nov. 



Shell small, rarely exceeding 12 mm. in width, transverse. Cardinal angles 

 rounded with the greatest width a little anterior. 



Dorsal valve moderately convex. 



Ventral valve strongly convex with a high, well-defined area which is con- 

 siderably narrower than the greatest width. Area slightly convex and strongly 

 oblique to the plane of the valves. Foramen rather broad. Beak strongly 

 projecting and moderately incurved. 



The surface is marked by rather few. very strong, high, rounded plications. 

 The fold and sinus are simple and distinctly larger and higher (especially the 



