90 
PALAEONTOLOGY OF NEW YORK. 
The specimens of casts from the Upper Helderberg limestone of New York, 
which at one time I thought might prove identical with this species, are in 
such a condition as to give no satisfactory assurance of identity. 
Formation and locality. In limestone of the Upper Helderberg group, at the 
Falls of the Ohio. 
Murchisonia desiderata var. 
PRATE XXI,-FIG. 10. 
Shell elongate, turretiform ; spire rapidly ascending. Volutions ten or more, 
regularly enlarging from the apex, the last one scarcely more ventricose 
than those above; obtusely angular at the peripheral band, which is 
below the centre, flattened above it, scarcely convex below it—this 
portion of the volution a little more than half as wide as the upper. 
Surface marked by fine close striae which, so far as observed, have the same 
character and direction as in M. desiderata; spiral band narrow and 
flattened, giving prominence to the volution at that point. 
The specimen is a mould of the exterior in chert, and the drawing is made 
from a gutta-percha cast; the striae are imperfectly preserved. The volutions 
are somewhat less convex than in M. desiderata, and appear to be more rapidly 
attenuate above. The mould shows a part of another volution below the last 
one represented in the figure, so that the shell has had at least eleven volutions 
in a length of about three inches. In the absence of other material for com¬ 
parison, and until we have the means of more satisfactory determination, I am 
disposed to regard this as a variety of the species already described. 
Formation and locality. In limestone of the Upper Helderberg group, at the 
Falls of the Ohio. 
