LAMELL1BKANCHS. Ill 



nearly flat. Ears subequal ; the anterior somewhat smaller 

 than the posterior, and with much more conspicuous radiating 

 costre. Surface marked by low radiating ribs, of which there 

 are about fifteen, that extend from the umbo to the margins, 

 the others disappearing as they approach the beaks. These 

 are crossed by numerous fine, often imbricated, lines of growth. 

 All the surface markings are much more prominent on the left 

 valve than on the right. 



Horizon and localities Upper Carboniferous, Upper Coal 

 Measures : Plattsburg ( Clinton county ), Kansas City. 



Aviculopecten carboniferus (STEVKNS). 

 Plate xliii, figs. 4a-b. 



Pecten carboniferus Stevens, 1858 : Am. Jour. Sci., (2), vo 1 . XXV, p. 261. 

 Pecten broadheadi Swallow, 1863: Trans. St Louis Acaei. Sci., vol. II, 



p. 97. 

 Pecten hawni Geinitz, 1866 : Carb. und Dyas in Nebraska, p. 36, tab. ii, 



tigs. 19a-b. 

 Aviculopecten carboniferus Meek, 1872: U. S. Geol. Sur. Nebraska, p. 193, 



pi. ix, figs. 4a-b. 

 Aviculopecten carboniferus White, 1884: Geol. Sur. Indiana, 13th Ann. 



Rep., pt. ii, p. 144, pi. xxxviii, figs. 5-6. 



Shell rather small, oblique, moderately convex, length and 

 breadth nearly equal ; hinge-line nearly or quite straight, and 

 somewhat less in length than the greatest 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 deep rounded sinus ; ante- 

 rior ear about two-thirds as long as the other, and rather more 

 distinct from the umbo and more obtuse, but still rather acutely 

 angular ; defined by a moderately distinct subangular sinus. 

 Eight valve nearly flat, or distinctly less convex than the 

 other ; its anterior ear narrow, and defined by a deep, rather 

 sharp sinus ; posterior ear of the same size and^form as in the 

 left valve. Surface ornamented in the left valve with about 

 fifteen or sixteen distinct, angular, radiating plications, sepa- 

 rated by furrows of the same size, each one of Which terminates 



