326 PALAEONTOLOGY OF ILLINOIS. 



directly downward into the cavity of the body, which was probably for 

 the passage of the arm-muscles. 



Looking at this specimen alone, one would naturally suppose there 

 must have been, during the life of the animal, two distinct openings in 

 the vault, as appears to be the case in the specimen of C. planus, Miller, 

 figured by Professor PHILLIPS and Mr. AUSTIN. But on examining 

 the specimen of C. loicenxiv mentioned above, we find that it shows the 

 base of the small lateral proboscis, with the five principal vault-pieces 

 alternating with the first radials (the one on the anal side being larger 

 than the others), and the same ainbulacral furrows extending inwards 

 from the arm-bases, all exactly as in the C. malvaceus. ]>ut here we 

 find the central opening undoubtedly closed by several vault pieces, 

 while the ainbulacral furrows, extending inward from the arm bases, 

 pass in under these central pieces, and are themselves occupied, or cov- 

 ered, by a double series of alternating, very minute pieces, which 

 probably also extend on all the way up the ainbulacral furrows of the 

 arms as marginal pieces.* 



From our examinations of these two specimens, which are the. only 

 examples of the genus we have seen, showing the vault pieces, and 

 seem to be typical forms of the genus in all other respects, we are 

 strongly inclined to think the specimen of C. planus, figured by Prof. 

 PHILLIPS and Mr. AUSTIN, has had these central vault pieces removed 

 by some accident. The fact that these pieces in the specimen examined 

 by us, in Mr. WACHSMUTH'S collection, seem not to be deeply implanted 

 between the five larger surrounding pieces mentioned, but rather rest, 

 as it were, parti}" upon the narrow bevelled points of the inner ends of 

 the latter, between the ainbulacral furrows, so as to allow room for 

 these furrows to pass under, would render them less firm, and more 

 liable to be removed by any accident, and may possibly account for 

 their absence in the English specimen mentioned. 



In regard to the pieces covering the central part of the vault, and 

 which, from the way they are arranged for the ainbulacral furrows to 

 pass under them, were apparently more liable to be removed than the 

 others, we would remark that they do not present the prominent ap- 

 pearance and uniformity of size and form of the movable pieces com- 

 posing what is often called the ovarian pyramid in the Cystids, but 

 certainly have all the appearances of true fixed vault pieces, and 

 scarcely project above the others surrounding tJiem. Consequently we 

 cannot believe it at all probable that this genus had a central mouth, 

 opening directly through the vault, though its ainbulacral canals evi- 

 dently converged from the arm-bases to the middle of the vault, partly 

 above the outer vault pieces, and under those composing the middle of 



- Sci> jilatc 9. li;:. 13. 



