PTEROPODA. 
213 
across the otherwise smooth intermediate space. Usually the crests of 
the ridges appear to be smooth and flat, and the pustules or tubercles are 
seen only under favorable conditions. This ornamentation of the surfaces 
is not visible to the naked eye. 
The surface characters, as given above, are from portions of the very thin 
shell preserved in many specimens, and from distinct impressions of the 
exterior in the softer shales from which the shell has been dissolved; also 
from the moulds of the interior, preserving in some degree the external 
ornamentation. 
The specimens are all imperfect; the largest fragment (making allowance 
for the absent portion) indicates an original length of about 100 millimetres, 
while the ordinary specimens are scarcely more than sixty-five or seventy 
millimetres long; the width, measuring the flattened faces, may have been 
about twenty to twenty-five millimetres. 
This species differs from all the others in our rocks in the interlocking of 
the striae along the median line of each face. The striae are proportionally 
more distant than in C. undulata and C. crebristriata , and are very similar in 
this respect to C. Cayuga, in which they are stronger and much more coarsely 
tuberculate, while the intermediate spaces are more strongly striate. In well 
preserved specimens, the transverse striae are sharply elevated and distinctly 
pustulose, and where partially exfoliated the crest is sometimes punctate from 
the breaking of the pustules. In its flattened condition, in the shales, the 
general appearance of this fossil is similar to C. congregata, in which the striae 
are more closely arranged, and the tubercles upon their summits much stronger. 
The pyramid is not so robust as in C. undulata, and has more nearly the degree 
of attenuation of C. crebristriata.. Compared with C. Newberryi, in which the 
striae are interrupted on the face of the pyramid, it is distinguished by its finer 
and more closely arranged striae and broader form. When occurring in the 
softer shales this species is flattened, the surface ornamentation often obscure, 
and the details difficult of determination. From the coarser shales, we have 
a few fragments in which the original form is pretty well preserved, and the 
surface-markings more distinct. 
