Bbede.J Carboniferous Invertebrates. 1.17 



the pallial border to the hinge, 15 mm. ; breadth, from the 

 anterior to the posterior margin, 1(> mm. ; convexity, 3 mm. 

 Right valve unknown.'' In the discussion they also add: 



11 This exceedingly beautiful species seems to have varied a 

 little in the details of its surface markings at different ages. 

 In young shells the regular concentric costse seem to be nearly 

 or quite smooth, but as the shell advanced in its growth, they 

 gradully assumed a regularly crenulated outline, and became 

 themselves ornamented with extremely fine longitudinal stria 4 , 

 not visible without the aid of a lens. These stria^ are very 

 much finer and less distinct than those occupying the spaces 

 between the costa\ The faint indications of radiating costa*, 

 seen crossing the concentric stria* in the depressions between 

 the concentric ribs, are also wanting in young shells." 



Range and distribution : Upper Coal Measures; Kansas City. 



The absence of radiating stria* and costa* and the strong con- 

 centric cosne with the fine concentric stria* between them easily 

 and clearly distinguish this species from all others of the genus 



Aviculopecten carboniferus. Plate XIII, fig:. 9. 



Pecten carboniferUs Stevens, Amor. Jour. Sci. and Arts, xxv, p. 2(51, 



(1858). 

 r^tm broadheadii Swallow, Trans. St. L. Acad. Sci., n, p. 97,(1862). 

 Pecten ham,,; Swallow and Geinitz, Carl), u. Dyas in Neb., p. 3(5, pi. n, 



IT. 10a, 1), I 1866). 

 Aviculopecten carbonifefus Meek, Fin. Rep. U. S. Geol. Surv. Neb., 

 p. 19.°,, pi. iv, f. 8, and pi. ix, (f. 4a, b, I 1872 |. 



Meek's description: "Shell rather small, slightly oblique, 

 moderately convex, length and breadth nearly equal ; hinge 

 line nearly or quite straight, and somewhat less than the great- 

 est breadth of the valves, provided with a marginal ridge in 

 both valves; basal margin regularly rounded. Left valve more 

 convex than the other ; posterior ear rather well defined from 

 the swell of the umbo, somewhat extended and terminating in 

 an acute point, separated from the margin below by a deep, 

 rounded sinus ; anterior ear about two-thirds as long as the 

 Other, and rather more distinct from the umbo and more ob- 

 tuse, but still rather acutely angular, defined by a moderately 

 distinct subangular sinus. Right valve nearly Hat, or distinctly 



