SPIRIFERiE OF THE UPPER HELDERBERG GROUP. 
193 
distinct, with a subnodose character, on the exfoliation of the shell. The 
mesial sinus, is usually very wide at its base, sometimes equal to half 
the length of the shell. 
The proportions of the shell are extremely variable, the length being 
sometimes greater than the width, while usually the width is somewhat 
greater than the length; and in some individuals the length and breadth 
are as two to three. 
The casts of the ventral valve show a small rostral cavity with short 
strong dental plates; the muscular area being small, quadrangular, and 
divided through the middle by a distinct septum. 
The interior of the shell of the ventral valve shows short strong hinge- 
teeth and very short incurving plates below, while the bottom of the 
cavity is divided by a distinct elevated septum. 
The dorsal cast shows marks of dental sockets, with strong muscular 
markings at the apex of the fissure. 
This species is nearly allied with S. joerlamellosa of the Lower Helderberg 
group, and is not always readily distinguished from that one. It is, however 
usually proportionally shorter on the hinge-line, and more quadrate in form, 
while it is not known to have as many plications as the older species. 
The dimensions vary from half an inch in length and breadth, to an inch and 
a half in length and breadth; while other specimens are an inch and a half in 
width by an inch in length. 
This species is not common in the rocks of New York, though having a pretty 
wide distribution. 
Geological formations, and localities. This shell occurs at the Helderberg 
mountains and Schoharie, in the Schoharie grit; and in the same region, in the 
Corniferous limestone. It is known in the latter rock at Stafford, Caledonia, Wil- 
liamsville in Western New-York ; Columbus, Ohio ; Falls of the Ohio river ; and 
in several localities in Canada West. 
[ Paleontology. IV.] 
25 
