MISSISSIPPIAN FOSSILS 



99 



Strophalosia is a small brachiopod with concentric wrinkles and 

 scattered spines. The spines are seldom preserved entire but their position 

 is indicated by the broken bases. The surface also has low wart-like bumps. 

 The genus is related to Avonia , Buxtonia, and Piety oclostus but these three 

 genera always have some radial ornamentation. Strophalosia beecheri (fig. 

 240) is common in parts of the Logan. 



Athyris is somewhat like Girtyella but is wider than high 

 and usually larger than species of Girtyella . A. lamellos a 

 (fig. 241) is common in parts of the Cuyahoga and Logan. 



Leptaena is a long-lived genus (Ordovician to Mississippian 

 easily distinguished by its shape (see Fig. 59) and the strong 

 concentric ridges which are larger than the fine radiating ones. L. analoga 

 is common in parts of the Cuyahoga. 



Avonia (fig. 242) is a spiny brachiopod, distinguished from Strophalosia 

 by the presence of radiating ornamentation. From Dictyoclostus and 

 Buxtonia it differs in having only a few radiating ridges whereas these genera 

 have abundant ridges on the entire shell. Three species of Avonia are 

 locally abundant in the Cuyahoga formation. 



Fig. 242 



Fig. 243 



Ptychospira is one of several genera ( Camarotoechia and Rhynchopora 

 are the other common ones) in which the shell has much the same character. 

 Ptychospira can be separated from the others by the small number of ridges, 

 ten or less, radiating from the beak. P. magna (fig. 243) is common in 

 some parts of the Logan. 



Fig. 244 



Camarotoechia and Rhynchopor a (fig. 244) are lumped 

 together here as they cannot be distinguished by the outside of the 

 shell. They have very characteristic internal structures which 

 are seldom preserved in our Mississippian specimens. Several 

 species of Camarotoechia are common in the Cuyahoga and a few 

 species of Rhynchopora occur in the Cuyahoga and Logan. 



Fig. 245 



Fig. 246 



scabricula (fig. 



The shell of Torynifer resembles that of Athyri s but is 

 more regularly oval. The ornamentation is unmistakable; it 

 consists of concentric rows of fine, closely-crowded, short spines 

 over the whole surface of the shell. T. pseudolineata (fig. 245) 

 is common in places in the lower part of the Logan. 



Buxtonia is another spiny shell, a productid (compare with 

 Strophalosia , Avonia , and the next genus). It has one very convex 

 and one almost flat valve. Both the concentric and radiating 

 ridges are strong in Buxtonia but the radiating ridges are inter- 

 rupted whereas they are continuous in Dictyoclostus . Buxtonia 

 246) is common in parts of the Logan formation of east-central Ohio. 



