SPIRIFERiE OF THE UPPER HELDERBERG GROUP. 
201 
The casts show considerable variation in the form and proportions of the mus¬ 
cular area, two examples of which are shown in figures 15 and 16, Plate 29. 
The cast of a ventral valve, Plate 34, figure 25, illustrates the character of a 
well-preserved specimen from the Hamilton group. 
This species has been recognised by Dr. F. Rcemer and M. de Verneuil as 
identical with the 8. cultrijugata of Europe. Without the means of comparing spe¬ 
cimens, I had supposed the American and European species to be identical; 
but Mr. Davidson has recently called attention to the existence of bifurcating ribs 
in the American species, while “ in all the figures published by Rcemer, Schnur, 
“ and Sandberger of 8. cultrijugatus , the ribs on the lateral portions of the shell 
“ are simple, and do not exceed about twenty on each valve ; but in a specimen so 
“ named in my possession from the Falls of the Ohio near Louisville, in America, 
“ and which I received likewise some years ago from Herr F. Rcemer, the ribs are 
“ small, and in some places bifurcated, and numbering about twenty-four in each 
“ valve.” 
The original figures of Dr. Rcemer represent the species with simple strong 
rounded ribs on each side of the mesial fold and sinus ; while the elevation in 
front is triangular as in our specimens. In the figures of Schnur,* the sinus in 
front is not triangular, but the sides approach to parallel, and the summit is 
arched rather than angular. It appears to me, however, that M. Schnur has indi¬ 
cated something like a bifurcation, or a depression along the centre of the larger 
plications, in figures 1 a, b ; though it must be confessed that the general expres¬ 
sion of the figures is somewhat different from our shell. The figures given by Mr. 
Davidson (loc.cit.), and referred with doubt to this species, have “six or seven 
“ strong simple ribs on each of the lateral portions of the valve.” This feature 
would preclude its association with our specimens, and indicates a nearer approach 
to some of the forms which I have referred to 8. macroihyris. 
Mr. Conrad has given the length of 8. acwninatus as inches. The specimens 
before me vary from one inch to two and a quarter inches in width, and from 
three-fourths of an inch to an inch and seven-eighths in length. 
Geological formations and localities. This species is not known below the Cor- 
niferous limestone, where it has been found in Albany and Schoharie counties, as 
well as at several localities in the central part of the State, and at Williamsville 
and Clarence-hollow in the western part of the State. It occurs in the same forma¬ 
tion at Sandusky and Columbus, Ohio ; at the Falls of the Ohio both in Louisville 
and Jeffersonville, and at Camp creek, Indiana. It is found in the Hamilton group 
* Palaeontographica, T. iii, pi. xxxiii, f. 1, a, b, c. 
[ Paleontology IV.] 
26 
