CHAPTER VII r. 



ECHINODERMS : CRINOIDS. 



Although the stemmed echinoderms are among the earliest 

 organisms, at present known, to record their existence in the 

 rocks of the globe, their importance as types did not assume 

 an ascendancy until toward the close of the Paleozoic. There 

 are now living in the existing seas only a few stray forms 

 of this once great proup. In Missouri, and other parts of the 

 broad Mississippi basin, the stalked feather-stars do not form 

 prominent faunal features until after the Devonian. At the 

 beginning of the Carboniferous a wide mediterranean sea 

 occupied the heart of the American continent ; and throughout 

 its congenial waters the crinoids flourished in lavish luxuriance. 

 It was during the deposition of these Lower Carboniferous 

 rocks that life over the interior of North America was so 

 remarkable for the immense development and expansion of 

 piscine and echinodermatous types — among the latter especi- 

 ally for the culmination of crinoidal and blastoidal forms. Not 

 only was the development of the Crinoidea phenomenal in the 

 number of species, but the extensive numerical representation 

 of individuals was most astonishing. So prolific was crinoidal 

 life at this period, that the disjointed skeletal remains form 

 great beds of what may be appropriately denominated a crinoi- 

 dal breccia; which, however, is seldom uniform in physical 

 characters — some layers being very hard and compact, others 

 easily crumbling, full of interstices, and with scarcely any finer 

 and cementing materials. Throughout are disseminated the 

 broken and shattered calyces, fragments of arms and portions 

 of stems. In the massive, compact beds the organic remains 

 have been more or less completely comminuted by the grind- 

 ing action of moving water. But frequently these layers are 



