74 PALEONTOLOGY ' OF OHIO. 



prominent. Attached valve discoid, very thin, deeply and broadly 

 notched on the posterior side ; the notch not extending quite to the 

 center of the valve; occupying nearly one quarter of the circumfer- 

 ence of the valve on the outer margin ; border of the notch thickened, 

 especially at the base, which is rounded, and the center marked by a 

 slightly projecting point. Interior of the free valve marked by two pro- 

 portionally large, elongate, ovate, diverging muscular prominences, leav- 

 ing corresponding pits on the casts of the shell, or on exfoliated speci- 

 mens; situated just below the beak, and extending to nearly or quite 

 one-fourth of the length of the valve from the apex. There are also two 

 other muscular impressions somewhat smaller in size, circular in form, 

 and situated near, the middle of the valve below the extremities of the 

 ovate imprints, and slightly more distant from each other. Beneath the 

 beak there is a slight thickening of the cardinal border. The muscular 

 markings of the lower valve have not been observed. 



Surface of the shell of the convex valve marked by fine, even, thread- 

 like, radiating stride; increased both by division and implantation, and 

 gradually, increasing in strength toward the border of the shell ; the in- 

 terspaces where the shell is perfectly preserved are flattened, the striae 

 appearing as raised lines on the surface. The attacbed valve is strongly 

 marked by irregular concentric undulations circling the valve parallel 

 to the margin, but interrupted at the border of the notch. 



Formation and locality : In the Hudson Eiver gi-oup in the vicinity of Cincinnati, 

 attached to Strophomena altemata most frequently. Collection of U. P. James, Esq. 



Genus CRANIA, Refzius. 

 Crania scabiosa. 



Plate 1, fig. 17. 



Crania scabiosa, Hall ; Ext. 20th Rept. State Cab., November, 1866, p. 13. 

 Crania scabiosa, Hall ; 24th Rept. State Cab., p. 220, pi. 7, fig. 15. 



Shell small, less than medium size, discoid or but slightly elevatedi 

 sometimes prominently and irregularly convex; irregular in outline, with 

 thickened margins. Apex of the dorsal valve eccentric, varying in 

 position in dififere nt individuals. Surface of the valves usually marked 

 by strongly lamellose lines of growth, which are sometimes obscured by 

 the roughness of the substance upon which they have grown, giving its 

 character and form to the shell by causing it to grow irregular, so as to 

 assume the feature of the body itself. Ventral valve thin, not preserv- 

 ing the muscular marking and other features of the interior in a condi- 

 tion for description. 



