No. 109.] 133 



This is a fine robust species, remarkable for its comparatively narrow 

 area, broad triangular foramen, and extended hinge. Some of the specimens 

 show traces of an indistinct plication in the middle of the mesial sinus of 

 the ventral valve, which would indicate the presence of a small longitudinal 

 depression on the mesial fold of the other valve ; but the only specimens I 

 have yet seen are much worn, and the shell more or less exfoliated. There 

 were probably fine radiating strise, though no traces of them remain on 

 any of the specimens coming under my observation. 



Geological position aiid locality. In limestone of the Ufper Helderbero- 

 group at Williamsville, Erie county, N.Y.; and in the same limestone 

 near Columbus, Ohio. Dr. Mann. 



Spirifer DIVARICATUS. 



Pal. N.Y. Vol.iv. 



Shell somewhat semicircular, breadth nearly double the length ; 

 hinge equalling the greatest width of the shell, abruptly angular 

 at the extremities : dorsal valve imperfectly known : ventral 

 valve convex ; mesial sinus broad, deep, becoming undefined at 

 the margins towards the front, rapidly narrowing and more 

 distinctly defined as it approaches the beak, ornamented by 

 numerous irregular bifurcating somewhat angular plications, not 

 more than one-half or one-third of which reach the beak; area 

 moderately wide, extending to the hinge extremities, arcuate, 

 transversely striate; foramen broad triangular; beak small, 

 incurved. Surface marked by fine obscure closely arranged 

 concentric striae. 



This species has come under my observaiion only in the condition of 

 casts, or specimens so much exfoliated as to leave much doubt in regard to 

 the details of the finer surface markings. It occurs in the same locality wiih 

 the last described species, from whi'-h it may at once be distinguished by 

 its more gibbous form, less extended hinge, broader area, and smaller as 

 well as bifurcating plications, which are as distinctly marked in the sinus 

 as upon the sides ; a character preserved even in the casts. 



Geological position and locality. In the limestone of the age of the 

 Upper Helderberg group at Williamsville, Eric county. 



