8 



to the extremities of the hinge ; foramen scarcely higher 

 than wide ; surface, in unworn specimens, marked by con- 

 centric, imbricating lamella?. 



Length, '07 to '18, width -08 to '21 of an inch. 



Locality. — Spergen Hill, la. ; Alton, 111. 



Spirifera bifurcatus. — Shell semi-elliptical in general 

 form; dorsal valve gibbous ; ventral valve depressed convex ; 

 plications, seven or eight, which appear to coalese towards 

 the cardinal margin ; mesial fold with a defined depression in 

 the centre, reaching half way to the beak ; surface longitu- 

 dinally striated and concentrically marked by fine lines. 



Length, *09, width *11 of an inch. 



Locality. — Spergen Hill. 



Spiriferina (Spirifer) spixosa, (Norwood and Pratten,) 

 occurs at Bloomington and above Alton, in the same asso- 

 ciation with the preceding. 



SPIRIGERA, D'Orbigny; ATHYRIS, McCoy. 



Spirigera (athyris) hirsuta. — Shell varying in form from 

 ovate to sub-circular ; beak prominent, slightly extended, 

 front compressed, sometimes faintly sinuate. Yalves nearly 

 equally convex, the dorsal (ventral) valve most convex to- 

 wards the beak; beak of dorsal (ventral) valve prominent, 

 incurved so as to bring the minute foramen nearly on a line 

 with the margin of the shell ; beak of the smaller valve 

 closely incurved beneath the beak of the opposite valve. 

 Surface ornamented by concentric, imbricating lamella), 

 which give origin to successive rows of minute spines. 



The cast shows faint impressions of radiating stria?, which 

 are not visible on the external surface of the shell. A nar- 

 row impressed line is sometimes shown down the centre of 

 the cast of the dorsal valve ; and a few specimens have a 

 shallow depressed groove down the centre of the shell from 

 beak to base in both valves. A cast of a large individual 

 shows about seven turns of the internal spire. 



Locality. — Spergen Hill ; Bloomington ; Alton. 



