118 



PROCEEDINGS OP THE ACADEMY OP 



Length -69 (100) ; width -65 (94) ; thickness of both valves -41 (59). 



From the Lithographic limestone of Louisiana, Missouri. White Collection 

 of the University of Michigan. Also from the sandstone at Weymouth, Me- 

 dina County, Ohio, 60 feet below the conglomerate. Whittlesey's Collection. 



Close observation is necessary to distinguish this species from 5. subtilita, 

 Hall. That species, however, is less lamellose, the ventral sinus does not 

 extend above the middle of the shell, and the flattening beneath the beaks of 

 the ventral valve is wanting. 



Spirigera biloba, n. sp. Shell broadly ovate in outline. Ventral valve 

 rather ventricose, with a prominent beak which is gradually recurved, and 

 apparently minutely perforate at apex. A deep, narrow, median furrow 

 begins at the apex and extends to the anterior margin ; from the bottom of 

 this the surface rises with a convex curvature to the summits of the two 

 rounded ridges which constitute the most prominent portion of the valve ; 

 from these summits the curvatures continue to the right and left margins, 

 which are thus rendered quite obtuse. The external surface is marked only 

 by a few faint incremental lines. Shell structure fibrous. Characters of 

 dorsal valve unknown. 



Length -16 ; breadth -16. 



Collected by A. Winchell in the Goniatite limestone at Rookford, Indiana. 



This shell has somewhat the aspect of a CentronAla or Terebratula, but its 

 structure is not punctate. The unique character of the mesial furrow distin- 

 guishes it from any known species of Spirigera. 



Spirigera Ohiensis, n sp., (Figs. A and Aa, Whittlesey, Proceedings Amer. 

 Assoc. Cincinnati, p. 220). Shell large, subcircular in outline, moderately 

 ventricose. Ventral valve regularly arched from beak to anterior margin, 

 having the cardinal slopes somewhat straight, and the lateral margins con- 

 siderablv compressed. Sinus shallow and broad, extending half way to the 

 beak. Surface marked by numerous delicate, subequidistant, rigid, concen- 

 tric stria?. 



Length 1*18 ; breadth 1'40. 



Akron, Ohio, 50 feet below the conglomerate. Whittlesey's Collection.^ 



This species differs from S. Hannibalen.tis, Swallow, in its less ventricosity, 

 especially around the margin, and in the absence of concentric lamellae ; it 

 differs from S. Missouriensis, Win., in its transverse form, more compressed 

 lateral margins, and its numerous and regular concentric stria?. In the last 

 character it resembles S. concentrica, but the mesial sinus (and probably fold) 

 is much less marked. 



Spirigera Hannibalensis, Swallow, occurs in the Lithographic limestone at 

 Clarksville, Missouri. White Collection of University of Michigan. 



SPIRIFERA, Sowerby. 



Spirifera centronata, n. sp. Shell of medium size, with an elongate, cus- 

 pidate hinge margin, and, aside from the cardinal extremities, a somewhat 

 semicircular general outline. Ventral valve of medium fulness near the 

 umbo, somewhat depressed between there and the margins ; beak elevated 

 above the cardinal line more than one-fifth the whole length of the valve, in- 

 curved and overhanging a very narrow area. A distinct and comparatively 

 deep sinus begins at the extremity of the beak, very gradually widening and 

 becoming ill-defined in the middle of the valve and beyond. External surface 

 marked by 36 to 40 ribs, of which from three to five fall in the mesial sinus. 

 The ribs disappear on the alate cardinal expansions. One or two concentric 

 furrows marking the middle region of the valve. 



Length along cardinal line, 1-23 (100); length from beak to anterior mar- 

 gin, *52 (42); greatest convexity of ventral valve, -11 (9). 



