70 PALEONTOLOGY. 



Producta costata, McCoy (1855), Brit. Pal. Poss., 4G0. 

 Froducta Flemingi var. sulcata^ McCoy, ib., 461. 



Productus costahts, Meek (1872), Palseont. E. Nebraska, in Haydeu's Eeport U. S. Geo!. 

 Survey Nebraska, 159, pi. vi, flgs. 6 a, b. 



Sliell ratlier under medium size, about as long as wide, measuring direct 

 from the beak to the front, but longer than wide, measuring over the curve 

 of the ventral valve; very gibbous, and strongly incurved, tlie curvature 

 increasing little from the front to the beak, and sometimes describing nearly 

 two-thirds of an entire volution on the ventral surface ; hinge-line about 

 equaling the greatest breadth of the valves. Ventral valve very gibbous, 

 with a well-defined mesial sinus extending from the umbonal region to -the 

 front; ears small, nearly rectangular, and rather distinctly arched; lateral 

 slopes rounding off nearly vertically to the ears; beak gibbous, and strongly 

 incurved, but scarcely passing within the hinge-margin; surface ornamented 

 with moderate-sized longitudinal costa?, which sometimes become a little 

 irregular in size on the anterior and anterior lateral slopes by some of them 

 bifurcating, or, in other cases, by two of them coalescing to form a larger 

 and slightly more prominent one, generally at the origin of a spine. Small 

 concentric wrinkles also give the visceral region a more or less reticulated 

 appearance, while the bases of ratlier stout spines are seen scattered over 

 the anterior and lateral slopes (generally on the larger costse) as well as 

 on the ears, or sometimes in a row along the sulcus or concavity between 

 each ear and the very abrupt swell of the umbo. Dorsal valve flattened- 

 concave in the visceral region, where it is marked by obscure costse. and 

 small concentric wrinkles ; interior with a slender mesial ridge, most sharply 

 elevated near the middle, and having the muscular scars prominent and near 

 the beak; reniform scars obscure, directed outward and a little forward from 

 the anterior side of the muscular scars. 



Length of a medium-sized specimen, measuring direct from the beak to 

 the front, 1.21 inches; measuring over the curve of the ventral valve, 

 about 2.20 inches; breadth, 1.25 inches. 



It is with considerable doubt that I have ventured to refer this shell to 

 the variable species P. costatus, though.it seems to be the form that has gen- 

 erally been Identified with that species in our Coal-Measures and the Lower 

 Carboniferous rocks of the Mississippi Valley. Although these American 



