48 OHIO FOSSILS 



Stomatopora arachnoidea differs from all the preceding species in that its tubes do not 

 grow parallel to each other; instead, they form a network of tubes irregularly branching from 

 each other and grow on other bryozoans; it is found in the entire Cincinnatian. 



BRACHIOPODA. The phylum is represented in our Ordovician rocks by many genera 

 and species and literally millions of individuals. Only the commoner species are included 

 here. As much as possible, they are identified by the outer characters of the shell. If a 

 specimen to be identified has both valves, it is not difficult to compare it with the descriptions, 

 although shells with a concave valve (e. g. Rafinesquina ) may give a little trouble at first. 



1. 



a) 





b) 



2. 



a) 





b) 



3. 



a) 





b) 



4. 



a) 





b) 



5. 



a) 





b) 



6. 



a) 





b) 



7. 



a) 





b) 



8. 



a) 





b) 



9. 



a) 





b) 



10 



a) 





b) 



Key to the Commoner Ordovician Brachiopods of Ohio 



( see p. 4 for use of keys ) 



Beak on margin of shell 3 



Beak near center of shell 2 



Concentric ornamentation only Crania 



Shell with diagonal rows of pits Trematis 



Concentric ornamentation stronger than radiating ornamentation 4 



Radiating ornamentation stronger than concentric ornamentation 5 



Shell bent downward at margin Leptaena 



Shell not bent downward at margin Sowerbyella 



Shell with less than 40 radiating ribs 6 



Shell with more than 40 radiating ribs 8 



Shell with sinus and fold 7 



Shell without sinus and fold Plectorthis 



Shell round and fat, sinus and fold distinct Lepidocyclus 



Shell round but thin, sinus and fold indistinct Zygospira 



Without sinus and fold 9 



With sinus and fold 10 



Ribs unequal, one coarse alternating with several fine ones Rafinesquina 



Ribs coarse and irregular, not alternating Strophomena 



Shell small (3/4 inch or less) and flat Resserella 



Shell large (more than 3/4 inch) and thick through Dinorthis and Hebertella 



Two species of brachiopods can be distinguished immediately 

 because the beak is not on one edge of the shell but roughly near 

 the center of it. These are both roughly circular in shape, with 

 nearly central beak. Crania scabiosa (fig. 58) was attached to 

 other objects, such as other brachiopods, and lacks the character- 

 istic ornamentation of Trematis ; Crania scabiosa is found in the 

 entire Cincinnatian. Trematis millepunctata is similar to C. 

 scabiosa but has diagonal rows of pits on the shell, which are 

 characteristic; it occurs in the McMillan formation. 



In most brachiopods the beak is on the edge of the shell along 

 Fig. 5« which the two valves are hinged; hence this edge is called the hinge 



line. All the remaining species of brachiopods described here have 



