20 



OHIO FOSSILS 



Bryozoans were common around coral reefs and elsewhere in the Devonian seas. Some 

 of them built wavy, fan-like colonies which have the appearance of lace. The brachiopods were 

 very abundant during the Devonian and some of the forms are easily recognizable, for example 

 the Spirifers, Strophomenas, Atrypas, and Leptaenas. During the Devonian, there was a 

 sprinkling of spiny brachiopods, the productids, which became much more important in the next 

 period, the Mississippian. 



Pelecypods were not common in the Devonian seas, except locally. Round clams, the 

 long clam, and scallop-like forms are among the commonest. The snails are conspicuous in 

 the Devonian fauna: large, top-shaped forms, long, thin-spired forms, and the curious, partly 

 uncoiled, sometimes spiny snails called Platyceras. Cephalopods are locally common in our 

 Devonian; there are both straight and coiled nautiloids, some of the latter strikingly ornamen- 

 ted with successvie frills around the shell, and a few 

 coiled ammonoids. 



The trilobites of the Devonian include some very 

 large forms such as Coronura whose tails are fairly 

 common in parts of the Columbus limestone. Smaller 

 forms such as Phacops with compound eyes and 

 Proetus with neatly margined head and tail are locally 

 common as well as some species with cheek spines. 

 At times, ostracodes swarmed in the Devonian seas 

 and many genera and species have been described. 



The crinoids must have been very abundant in 

 parts of the Devonian seas, judging by the huge accu- 

 mulations of their stems which are found in parts of 

 the Columbus limestone. Several genera and species 

 of crinoids have been found in the Devonian of Ohio. The 

 curious, nut-like blastoids were sometimes abundant 



=FtSs\ Ohio shale 100' 



/ ,~\ Ten Mile Creek dolomite 40' 



j. Silica formation 40' 

 Blue limestone 10' 



Columbus limestone 55' 



Lucas dolomite 120' 



r ~ \ 



)' ' ./. ■' ' T^\ Amherstburg dolomite 10' 

 I Sylvania sandstone 40' 

 Fig. 20b 



Ohio shale 600' 



Olentangy shale 20 

 Delaware limestone 45' 



Columbus limestone 100' 



Devonian rocks of northwestern Ohio 



Fig. 20a 



Devonian rocks of central Ohio 



