Bracldcpoda cf the Chtcinnati Group. 11 



Leptobolus ??/))>— (Hall, 1871). 



Shell minute, ovate, or broadly elliptical in outline, about fths as 

 Avide as long, and seldom exceeding ^l^^ths of an inch in length; 

 moderately convex, the greatest convexity being about one third of the 

 length from the 1)eak ; ventral area thickened ; pedicle groove strongly 

 defined ; muscular impression broad, extending more than one third 

 the length of the valve ; muscular ridges of the dorsal valve strongly 

 marked, the central one extending two thirds the length of the 

 shell, the lateral ones diverging from each other at an angle of 

 about 45°, and extending nearly to the middle of the valve; extremi- 

 ties bifid. Surface of the valves concentrically marked by fine lines 

 of growth. 



Found on the clay nodules below Mowry's foundry, in the first ward 



of the city of Cincinnati, within twelve feet of low Avater- 



mark, associated Avitli Leperdlt'm Btjrnesl and Lichenocriniis crateri- 



formis Its range, so far as knoAvn, is confined to the lower rocks of 



the Cincinnati Group. 



Family CmnUdce—(D'ORB). 



Shell thick, pyramidal, calcareous, Avithout muscle of attachment ; 

 free or fixed by the substance of the loAver or ventral valve ; arms 

 spirally fixed among themselves, not extensile, nor supported by 

 apophyses ; thickened margin of the valves, Avith ramified impressions 

 of the fimbriated edge of the mantel. 



This family includes the genera Crania and Pholidops. 



Genus Crania — (Ketzius. 1781). 



[E/ym. —Krancia, capitate.] 



Shell A^ariable in shape, inequivalve, circular, subquadrate, trans- 

 verse or elongated, partially or extensively attached by the substance 

 of its loAver or ventral valve ; rarely free ; upper or dorsal valve more 

 or less conical, vertex subcentral ; no articulated hinge or ligament, 

 the A-alves being kept in place by the action of four muscles, Avhich 

 pass in a somcAvhat oblique manner from one A^alve to the other ; the at- 

 tached or ventral valve is generally the thickest, Avith or without a 

 straight more or less produced beak, and false area. External surface 

 smooth, spiny, or variously ornamented by radiating costa> or foliaceous 

 expansions ; the concentric lines of growth passing uninterruptedly over 



