MONOGRAPH OF THE EXISTING CRINOIDS. 185 



proached by certain palaeozoic species, differs from them in many details of general 

 structure. 



Very possibly the most primitive type of crinoid existed in the palaeozoic 

 aloiig with the typos which have come down to us as fossils in the rocks; but, as the 

 remarkable density of the crinoid skeleton is a feature developed within and chur- 



FIG. 119. LATERAL VIEW OF A SPECIMEN OF PENTAMETROCRINUS VAEIANS FROM SOUTHERN JAPAN, SUOWTNG 

 THE RELATIVE PROPORTIONS OF THE ARMS, PINNULES, CENTRODOKS.U., AXI> CIRRI. 



acteristic of the group, they were undoubtedly small and delicate creatures with 

 a very poor chance for preservation. 



Exactly the same was the case with the primitive birds. They were un- 

 doubtedly, judging from all the evidence at hand, small and arboreal, not large 

 and terrestrial, and therefore stood almost no chance of ever being preserved. 



79146 Bull. 8215 13 



