8G TRANS. OP THE ACAD. OP SCIENCE. 



SPIRIFER IvELLOGGII. 



Shell small, convex, transverse. Ventral valve high ; me- 

 sial sinus simple, narrow, deep ; beak but little incurved ; 

 area high, arched, as long as the width of the shell; foramen 

 narrow, closed at top. Dorsal valve smaller, less convex ; 

 mesial fold simple, narrow, and high. Surface marked with 

 six or seven simple plications on each side or* the mesial fold 

 and sinus, and by fine, equal, imbricating, concentric lamellae. 



This shell resembles the S. sfmiosus of Norwood & Prat- 

 ten ; but its markings are different, having no spines and 

 punctae as that species. 



This fossil is common in the lower beds of the Keokuk 

 Limestone and the upper Chert beds below, where it is asso- 

 ciated with 0. Keokuk, S. neglectus, P. vittatus, P. grada- 

 tus, and S. pseudolineatus. Collected by Dr. Kellogg. 



Spirifer i^evigatus. 



Shell large, transverse, sinuate, and smooth. Ventral valve 

 moderately convex ; beak moderately incurved ; sinus broad, 

 deep, regularly concave, extending from the beak to the an- 

 terior margin ; area large, arched, as long as the width of the 

 shell; foramen large, triangular, nearly as wide as high. Siir- 

 face smooth. Dorsal vedve not known. 



It is a common shell in the lower beds of the Keokuk 

 Limestone in Iowa and Missouri. 



Spirifer latior. 



Shall rather small, transverse, semiorbicular, lateral ex- 

 tremities long and pointed. Ventral valve convex, highest 

 near the beak; beak small, slightly incurved ; area large, sub- 

 triangular, as long as the width of the shell ; foramen trian- 

 gular, higher than wide; sinus well defined, marked with 

 one large central fold, and one smaller on each side. Dorsal 

 valve less convex; beak small, scarcely incurved; mesial fold 

 well defined, depressed, marked with four plications. Sur- 

 face marked with about sixteen rounded plications on each 

 side of the mesial fold and sinus; plications rarely forked. 



This rare fossil is found in the Chouteau Limestone of 

 Cooper county, Missouri. 



Spirifer clartjs. 



Shell small, convex, lenticular, decussate, sinuate. Ventral 

 valve very convex; umbo large; beak small, strongly incurv- 

 ed ; area small, triangular, length equal to one third of the 



