THE MISSISSIPPIAN PERIOD 



609 



the crinoids were most prolific, as indicated by the fact that a single 

 genus (BatocrinuSj} had more than a hundred species. The orna- 

 mentation of the crinoids at this time was notable, and as in the 

 case of' the trilobites, preceded the decline of the group. The 

 repetition of this singular phenomenon at different times, and in 

 quite different groups of organisms, is worthy of notice, though its 



Fig. 430. Osage Echinoderms: a-c, crinoids; a, Barycrinus hoveyi Hall; 

 6, Eretmocrinus remibrachiatus (Hall), having peculiar spatulate arms; 

 c, Actinocrinus lobatus Hall, shows highly ornamented plates; d, Forbesi- 

 ocrinus wortheni Hall, a flexible crinoid; e, a blastoid, Oligoporus mutatus 

 Keyes. 



meaning is not altogether clear. The crinoids made large contri- 

 butions to the limestone of the period, the "encrinital limestone" 

 taking its name from the numerous plates and stems which make 

 up much of its substance. Other echinoderms were not* very 

 abundant. 



It is a matter of surprise that the corals had so small a place in 

 this fauna, in view of the favorable physical conditions. It is 



