118 
PROCEEDINGS OF THE ACADEMY OF 
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 S. 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 Groniatite limestone at Rockford, Indiana. 
This shell has somewhat the aspect of a Centronella or TerebraUila, 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¬ 
siderably compressed. Sinus shallow and broad, extending half way to the 
beak. Surface marked by numerous delicate, subequidistant, rigid, concen¬ 
tric striae. 
Length 1*18 ; breadth 1*40. 
Akron, Ohio, 50 feet below the conglomerate. Whittlesey’s Collection. 
This species differs from S. Hannibalensis, 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 striae. 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). 
fJuly, 
