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. Tn limestone of the Upper Helderberg group, at the 

 Falls of the Ohio. 



MURCHISONIA DESIDERATA Var. 

 PLATE 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. / 



