154 [ Senate 



Geological position and locality. In the shales of the Hamilton group : 

 rarely in Eastern New- York, more common in the central and very abun- 

 dant in the western part of the State, and particularly on the shore of 

 Lake Erie at Eighteen-mile creek. 



SpIRIFER FORMOSA ( n. S.). 



Pal. N.Y. Vol. iv. 



Shell somewhat semicircular, two-thirds to four-fifths as lorg as 

 broad, moderately ventricose ; hinge equal to the greatest 

 width of the shell, slightly salient at the extremities ; valves 

 about equal : dorsal valve regularly convex, having a flattened 

 mesial fold, on each side of which there are from fifteen to 

 seventeen rounded plications ; beak incurved : ventral valve 

 most prominent near the umbo ; mesial sinus shallow, flat in 

 the middle, and distinctly limited by the adjacent plications; 

 beak somewhat prominent, arched or incurved ; area moderately 

 high, arcuate, sloping from the beak to the extremities of the 

 hinge ; foramen distinct, wider than high. Surface marked by 

 fine regular concentric striae, which arch upwards in crossing 

 the mesial fold : faint traces are sometimes seen of extremely 

 fine radiating striae. 



This is a neat symmetrical species, with a gracefully curved outline and 

 salient angles. In profile, the beak of the ventral valve projects but little 

 beyond that of the dorsal valve. The mesial fold, which is usually flat in 

 the middle and lower part of the shell, is distinctly grooved along the 

 centre in the upper part, and this depression sometimes continues to the 

 base. 



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

 milton group : Illinois. 



Spirifer fornacula ( n. s.). 



Pal. N.Y. Vol. iv. 



Shell (dorsal side) nearly semicircular, from two-thirds to three 

 fourths as long as wide j hinge equalling the greatest width of 



