DEVONIAN FOSSILS 



85 



knows what its function was in the living animal. Conocardium is found from the Ordovician 

 to the Permian but in Ohio it is commonest in the 

 Devonian. C. cuneus occurs in the Columbus and 

 Delaware. 



Grammysia (fig. 189) seems to be cut off at 

 one end. It is easily recognized by the ribs, of 

 which there are only a few in the central part of the 

 shell. Several species are found in our Devonian 

 rocks. 



Modiomorpha is very like some of our present- 

 day river clams in appearance. The shell is swollen 

 at the end away from the beak and it lacks the inter- 

 nal ridge of Nuculites. M. concentrica (fig. 190) is 

 our common species. 



The most characteristic feature of Nuculites is the 

 internal ridge which shows as a groove in internal molds. 

 Nuculites triqueter (fig. 191) is found in the Olentangy and 

 Plum Brook. 



Sanguinolites has closely spaced concentric ridges. It is 

 larger and more elongate than Nuculites . j^. sanduskiensis (fig. 

 192) is found in the Columbus. 



Schizodus can be recognized by its squarish outline, evenly convex shell, 

 thicker in the region of the beak. _S_. appressus (fig. 193) occurs in the Columbus, 

 Olentangy, and Plum Brook. 



Paracyclas might well be called the 'round clam. " It is almost round in 

 outline and has sharp, closely spaced concentric ridges. Some of the less- 

 rounded species may belong in the genus Phenacocyclas of which one species, 



Fig. 190 



Fig. 191 



Fig. 193 



formerly called Paracyclas , occurs in the Dundee. 

 Paracyclas elliptica (fig. 194) occurs in the Columbus, 

 Delaware, and Prout. 



GASTROPODA . 



fairly common 



Fossil snails large and small are 

 in our Devonian rocks. As for the Silurian, 



the long-spired forms are described first, then the shorter- 

 spired ones. The first six genera are higher than wide, the 

 next five are about as high as wide, and the last seven are 

 wider than high. 



