PTEROPODA. 
181 
gracilistriatus, having the general aspect of a large individual of the former, and 
distinguished by the extremely fine longitudinal striae, which are visible under a 
magnifier. A few specimens only of this variety have been observed, occurring 
upon the surface of a slab of shale, which shows several hundreds of the 
smaller forms. 
Formation and locality. In a grey shale at the base of the Hamilton group. 
Styliola fissurella, var. intermittens. 
PLATE XXXI A, FIGS. 11-17. 
Shell a minute, extremely elongate-conical tube, having a length of from one 
and a half to five mm. Surface marked by fine transverse striae, which 
appear to be crowded, or the shell thickened at regular or irregular inter¬ 
vals, giving an undulated or obscurely annulated appearance. This feature 
is often more conspicuous in specimens where the shell is partly exfoliated. 
In this respect it may be compared with Tentaculites intermedius of Barrande, 
in which the annulated character is more obscure. 
This form, which cannot be separated from S. fissurella by any constant and 
reliable characters, presents much variety of aspect in its different conditions, 
and the same individual sometimes combines all the features observed in the 
species. The transversely striate character is rarely regular or uniform, but 
usually somewhat fasciculate, and prevailing over all other surface marking, 
while not unfrequently there are obscure indications of longitudinal striae, which 
in m<yny individuals assume an equal strength with the transverse markings, 
and present a minutely cancellate structure. It not unfrequently happens that 
these markings are not uniform over the entire surface of the same individual, 
and the variation is so great as to preclude the possibility of recognizing as dis¬ 
tinct species any of the forms here noticed. 
The illustrations of S. fissurella on plate XXXI A, represent the principal 
phases of this very variable fossil as presented in the Marcellus shale, the 
Hamilton group, and the Genesee slate. In the Cashaqua shale and the 
succeeding shaly rocks of the Portage group these fossils are usually in such a 
