Monograpli of the Lamellihranclnata. 221 



the posterior basal extremity to the front ; anterior margin short or 

 truncated from immediately in front of the beaks obliquely downward 

 and backward to the base, which it joins at an obtuse, slightly rounded 

 angle ; hinge line very short, ranging at an angle of about fifty degrees 

 to the umbonal axis, and apparently having its margins a little inflected 

 behind the beaks; beaks very prominent, oblique, nearly or quite ter- 

 minal, and strongly incurved ; posterior umbonal slopes subangular 

 near the points of the beaks, but becoming rounded below, while the 

 dorsal region between this and the hinge is a little concave ; anterior 

 umbonal slopes forming a kind of ridge, that extends at something less 

 than a right angle to the hinge to the anterior basal margin, tlie an, 

 teiior side, thus circumscribed, being somewhat flattened, and, as seen 

 from the front, presenting a cordate outline. Surfoce ornamented with 

 small, very regular, simple, concentric costie, that seem to be obsolete 

 on the anterior and posterior portions of the valves. (Hinge and 

 interior unknown). 



Length parallel to the cardinal margin, about 0.45 inch; height, 

 at right angles to hinge, to the tops of the beaks, about 0.45 inch; 

 length, measuring from the points of the beaks obliquely, to the j)OS 

 terior basal extremity, 0.57 inch ; convexity, 0.39 inch. 



Found near the top of the hills back of Cincinnati. Range un- 

 known. 



Genus Orthoiiota — (Conead, 1841). 

 Shell elongated, margins parallel, umbones anterior, back plaited. 



Orthonota jmrallela — (HAll, 1847). 



Shell extremely elongated and very narrow ; anterior extremity 

 rounded, and contracted just forward of the beaks ; cardinal margin 

 straight or gently arched ; posterior extremity rounded, broader than 

 the anterior ; basal margin slightly arcuate ; beaks near the anterior 

 extremity having an obscure carina, extending obliquely toward, but 

 not reaching, the posterior basal margin ; surflxce marked by fine con- 

 centric strise, and a few oblique, strong wrinkles, along the dorsal 

 margin. 



Width one third the length. In specimens embedded in shale, and 

 much compressed, the surface is regularly convex, and the oblique, 

 elevated carina, becomes obsolete. The cast is smooth, with scarcely 

 any evidence of the oblique folds on the cardinal margin. 



This fossil is known only as a cast, which is by no means abundant. 

 It is found at the quarries about Cincinnati, but its range is not known. 



