128 [Senate 



the hinge : ventral valve most prominent near the umbo, having 

 about ten simple rounded plications on each side of the sinus, 

 in which are four to seven smaller bifurcating plications ; beak 

 projecting above the opposite one, incurved ; foramen triangu- 

 lar ; area short, broad, triangular, strongly arcuate. Surface 

 marked by regular, strongly undulating, subimbricating lines 

 of growth, which are crossed by fine radiating striae, giving the 

 edges of the lamellae a fimbriated appearance. 



This species is distinguished from most of the allied forms by its simple 

 strong plications on each side of the mesial fold and sinus, while those 

 occupying the same are smaller and bifurcating. Sometimes the middle 

 plication on the summit of the mesial fold is simple, in which case the fold 

 is quite angular ; while in other instances it bifurcates, leaving a longitu- 

 dinal depressed line on the middle, giving it a more rounded outline. It is 

 only on specimens which have suffered no injury by wearing or exfoliation, 

 that the fimbriate appearance of the concentric marliings is visible. 



Geological position and locality. Gray limestone of the age of the Upper 

 Helderberg group, near Columbus, and also near Sandusky, Ohio. 



I am indebted to Judge Grier of Dayton, Ohio, for this and other 

 specimens. 



Spirifer manni ( n. s.). 



Pal. N.Y. Vol. iv. 



Shell triangular-semioval, very gibbous ; hinge straight, equal to 

 the greatest width of the shell, angular at the extremities : 

 dorsal valve nearly semicircular, convex, having a distinct me- 

 sial fold which is depressed or faintly grooved along the middle, 

 giving the lateral margins great prominence ; on each side of 

 the mesial elevation, about ten or eleven simple rounded plica- 

 tions ; beak and narrow area strongly incurved : ventral valve 

 extremely prominent at the umbo and sloping laterally, having 

 about eleven simple rounded plications on each side of the deep 

 smooth mesial depression ; beak not incurved ; foramen narrow ; 

 area very wide, slightly arcuate. Surface unknown. 



