66 



OHIO FOSSILS 



Fig. Ill 



Fig. 112 



Fig. 113 



In Parmorthis ( Dalmanella in older publications) the sinus and fold are in- 

 conspicuous (fig. 111). Two species are common in the Niagaran. 



Eospirifer i s another spiriferoid (see Crispella above). It has a strong si- 

 nus and fold and its wing-like shell will easily distinguish it from Parmorthis. 

 E. radiatus (fig. 112) is the commonest of four species found in the Niagaran. 



In Rhipidomella hybrid a (fig. 113) the hinge line is less than half the width 

 of the shell and the valves are almost equal in thickness. It is common in the 

 Niagaran. 



Atrypa reticularis (see fig. 182) has one thick and one thin 

 valve. It is common in the Niagaran. 



PELECYPODA. Only three species are common enough in 

 our Silurian rocks to merit notice here. Since they are very dif- 

 ferent from each other, they can be distinguished from the descrip- 

 tions and figures; no key is needed for them. 



Megalomus canadensis (fig. 114) is generally found as intern- 

 al molds, called ''beef hearts" by the quarrymen. The name is de- 

 scriptive and the genus cannot be confused with any other, except pos- 

 sibly Amphicoelia , because of its size. Megalomus has no radial or- 

 namentation, a conspicuous character of Amphicoelia . 



Amphicoelia costata(fig. 115) is a large pelecypod (2. 75 inches 



Fig. 114 



Fig. 115 



long) with the beaks near one end of the shell. The surface has prominent 

 but small radiating ribs. It is common in the Cedarville. 



Pterinea brisa (fig. 116) can be separated from both Megalomus 

 and Amphicoelia by its wings, which these two genera lack entirely. 

 P. brisa is rare in the Springfield and common in the Guelph. 



Fig. 116 



GASTROPODA . Fossil snails are fairly numerous in our Silurian, some of them large 

 enough to attract immediate notice, others so common in some beds that they are frequently 

 collected. Some of the cephalopods are also coiled like snails; large coiled mollusks should 

 be examined for septa before they are keyed out as gastropods. The commoner gastropods 

 may be identified by the following key. 



