102 



OHIO FOSSILS 



The only common scallop-like pelecypod in our 

 Mississippian is Aviculopecten which can be recognized by 

 the ''wings'' on the margin of the shell. A. winchelli (fig. 

 254) is common in parts of the Logan. 



The outline of the shell in 

 Grammysia (fig. 255) is variable, 

 hence the genus appears twice in the 

 key. Whether the shell is short or 

 long, the large beaks, the concentric 

 ridges, and the strong angulation from 

 the beak to the margin will identify 



these shells. One species is common in both the Cuyahoga and the 

 Logan; three others are rare in the Logan. 



Fig. 255 



Palaeoneilo has a characteristic outline (fig. 256) which will help identify it. 

 In addition, internal molds show numerous small teeth perpendicular to the hinge. 

 Fig. 256 Three species of Palaeoneilo are common in the Logan. Others are found rarely 

 in other formations of the Mississippian. 



Allorisma (fig. 257) is a large clam with large beaks 

 which can be recognized by the characters given in the key. 



It is abundant in some beds of the Logan 

 but specimens are usually crushed and 

 broken. 



Fig. 257 



Fig. 258 



The external surface in Nuculana (fig. 258) is covered with 

 closely crowded concentric grooves; internal molds show teeth of the same character as 

 those of Palaeoneilo but the shape of the shell is sufficient to distinguish them. A few 

 species are common in parts of the Logan. 



The shell of Parallelodon 

 Fig. 259 (fig. 259) is about the same size 



as that of Allorisma but the proportions are 

 different and Parallelodon lacks the distinct 

 concentric ridges of Allorisma . Parallelodo n 

 depressus is abundant in the Logan. 



In Sanguinolites the beak is very near Fig. 260 



one end of the shell and the greatest height 



is not in the region of the beaks. S. websterensis (fig. 260) is abundant in some beds of the 

 Logan and is also found in the Cuyahoga. 



The common species of Sphenotus , S_. aeolus (fig. 261) 

 is an elongate clam. It has a well-marked ridge from the 

 beak to the margin. It is abundant in some beds of the Logan. 



Fig. 261 



