DEVONIAN FOSSILS 



93 



head is lobed and bulges out in 

 front. The tail has many spines, 

 two on each end of most of the 

 segments, none terminal. Three 

 species are found in the Columbus. 



BLASTOIDEA . Two genera 

 of blastoids are common enough in 

 our Devonian rocks to deserve 

 notice. This does not mean that 

 they will be found easily for they 

 are not common everywhere. They 

 are found in numbers only in 

 certain beds of the Columbus and 

 Delaware, usually silicified. 



Fig. 230 



Codaster has a cup with decidedly 



pointed ends and five indentations in 

 the top half of the cup, whereas 

 Nucleocrinus is melon-shaped and has 

 rounded ends. C. pyramidatus (fig. 

 230) is found in the Columbus lime- 

 stone. 



toids go, 

 have bee 

 from the 



Nucleocrinus is large, as bias- Fig. 231 



and lacks the strong indentations of Codaster . The best specimens are the ones that 

 n silicified and weathered out of the rock. N. verneuilli (fig. 231) has been recorded 

 Columbus limestone. 



CRINOTDEA. Specimens of this group cannot be called common in the Devonian of Ohio. 

 Still, six genera are collected often enough to justify inclusion here. The following key will 

 separate reasonably well-preserved cups but the majority of specimens collected are disap- 

 pointingly fragmentary. 



Key to the Commoner Devonian Crinoids of Ohio 



(see p. 4 for use of keys) 



1. a) Height and width of cup about equal 2 



b) Width of cup greater than its height 4 



2. a) Plates of cup convex Melocrinites 



b) Plates of cup not convex 3 



3. a) Surface of plates granular ("warty") Arthroacantha 



b) Surface of plates smooth Hexacrinites 



4. a) Surface of plates smooth 5 



b) Surface of plates with radiating ridges Dolatocrinus 



5. a) Base of cup conical Euryocrinus 



b) Base of cup flattened 6 



6. a) Plates very convex, some ending in a point Gilbertsocrinus 



b) Plates moderately convex, not pointed Megistocrinus 



