82 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Specimens are from the Kinderhook group, and presumably from Iowa, 
although their exact locality is uncertain. 
The general form and proportions of these spines agree with New- 
berry’s description of the type of C. depressus,’ which is likewise from 
the Kinderhook, and is now preserved in the Walker Museum of Chicago 
University. As the latter specimen is more or less abraded, it might be 
supposed that we have to do here with more perfect examples of the 
same species. It is certainly true that they all possess one character 
in common : and that is the extreme obliquity of the line of insertion, 
which extends for fully two-thirds the length of the spine. But unless 
both the description and drawing of Newberry are at fault, the differ- 
ences immediately to be pointed out are sufficient to warrant the 
recognition of a distinct species. 
According to Newberry, the lateral faces of C. depressus are ‘‘ marked 
with about thirty longitudinal ridges,” the tuberculation of which is 
“inconspicuous ;” and it is further stated that “along the anterior 
border the ridges are set with closely approximated, simple and plain 
tubercles; on the sides the longitudinal ridges are nearly or quite 
smooth.” But the two specimens here placed in a distinct species have 
much finer and more numerous longitudinal costz than are represented 
as occurring in C. depressus, and these can by no means be described 
as “inconspicuously tuberculose.” On the contrary, they are very 
prominently decussated, the transverse ridges being sharp and fine, and 
so closely crowded that as many as from seventeen to twenty are to 
be counted within the length of one centimeter. These decussations, 
when completely formed, extend entirely across the cost in a trans- 
verse or oblique direction, but their growth is frequently arrested, so 
that they appear as denticulations spaced at intervals of their own 
length along either side of the costae. The ten filiform coste lying 
next to the posterior margin are so closely apposed as to be almost 
contiguous, and these are surmounted by small conical tubercles, none 
of which are striated, however. Nor are any of the other transverse 
ridges striated. 
The remarkably oblique line of insertion is fully 10 cm. long in the 
type, and the pulp cavity remains open for the whole of this distance, 
or for more than half of the total length of the spine. The section 
shown in text-figure no. 10 A is taken at the point where the line of inser- 
tion meets the posterior margin. The latter is beset from this point 
onward to the apex with very small and closely spaced conical protuber- 
1 Newberry, J. S., Trans. New York Acad. Sci., Vol. XVI. (1897), p. 291. 
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