82 BULLETIN: MUSEUM OF COMPAKATIVE 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 (7. depressus,^ which is liliewise 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. Bat 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 costaj 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 costfe 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 costa:. The ten filiform costcB 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 tlian half of the total length of the spine. The section 

 shown in text-figure no. 10 ^ is taken at the point where the line of insei'- 

 tion meets the posterior margin. Tlie 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. XVL (1897), p. 291. 



