1869.] ilZEK AST) WOBTHEN- OX PAT.TIOZOIC CBESOIDILA. 4S7 



a comparatiyely large furrow e2:teBds inward from each arm-base 

 to the central opening. These we regard as continiiatioDS of the 

 ambulacral farrows from the arms, thongh there is also a miaate 

 openins at each arm-base, passing 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 natar^j suppose 

 there must have been, during the life of the animal, two distinct 

 openings in the vault, as apfiears to be the ease in the specimoi 

 of C. planu.?. Miller figured by Prof. Phillips and >Ir. Austin. 

 But on esamioins the sj:>ecLmen of C. loncensis mentioned above, 

 we find that it shows the base of the small lateral probcsds, with 

 the five principal vault-pieces altematii^ with the first radiak 

 the one on the anal side being larger than the others, and the same 

 ambulacral furrows extending inwards fit>m the arm-bases, all 

 exactly as in the C. mahacKUs. But here we find the central 

 opening undoubtedly closed by several vaiilt-pieees, while the 

 ambulacral furrows, extending inward from the arm-base, pass 

 in under these central pieces, and are themselves occupied, or 

 covered, by a double series of alternating, very minute pieces, 

 which probably also extend on. all the way up the ambulacral 

 fnrrows of the arms as marginal pieces. 



From our examinatiocs of these two specimens, which are the 

 only examples of the genus we have seoi, showing the vauk-piece^ 

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

 we are strongly inclined to think the specimen of C. pkmuSj 

 fiarured by Prof. P hilli pg and Mr. AustiUj has had these cQitral 

 vault-pieces removed by some ac-cident. The fact that these 

 pieces in the specimen examined by us. in 3Ir. Wachsmuth's 

 collection, seem not to be deeply implanted between the five larger 

 surrounding pieces mentioned, but rather rest, as it were, partly 

 upon the narr>?w bevelled points of the inner aads of the latter, 

 between the ambulacral 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 p'D^bly 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 ambulacral 

 ftirrows to pass under them, were apparently more liable to be 

 removed than the others, we would remark that they do not 

 present the prominent appecirance. and uniformity of size and 



