ORDOVICIAN FOSSILS 



53 



ANNELIDA . Worm tubes belonging to two genera are found 

 sparingly, attached to brachiopods and other shells. In Cornulites 

 the tube is straight or nearly so, small (up to 1 inch in length), and 

 ornamented with irregular ring-like thickenings. It may be mis- 

 taken at first for a crinoid stem, but the fact that it increases rap- 

 idly in size and is attached to other objects will set it apart from 

 the crinoids. Several species of Cornulites have been found in the 

 Maysville and a few in the Richmond. 



In Spirorbis (see fig. 43) the shell is coiled like a snail's but 

 is always attached to some other object, often a brachiopod, which 

 snails never are. Spirorbis cincinnatiensis has been described 

 from the Maysville. 



OSTRACODA. Shells of these arthropods, which look like 

 tiny pelecypods (see fig. 134), are found, sometimes abundantly, 

 in our Ordovician. They will escape notice unless a special search 

 is made for them, but their beauty and odd ornamentation will re- 

 pay the trouble involved. Their identification is a job for a spe- 

 cialist. 



ARACHNOIDEA . Eurypterids existed in Ohio during Ordo- 

 vician time but their remains are usually rare. Megalograptus ,, 

 a spectacular form with abundant spines, scales, and bristles, 

 has been found in the Upper Elkhorn near Manchester, Ohio. 

 An equally rare eurypterid-like animal, Neostrabops martini , 

 has been found in the McMillan formation of Clermont County 

 (see Caster and Macke, 1952). 



TRILOBITA. Complete trilobites are rare. In some beds 

 of the Cincinnatian they may be found in fair abundance, gener- 

 ally rolled up with the tail shield fitting snugly against the head. 

 Trilobite fragments are abundant in some beds; the head and 

 tail shields can be identified at least to genus but the thoracic 

 (middle -of -the -body) segments are hopeless except for an ex- 

 pert. The following species are among the least rare. 



Key to the Commoner Ordovician Trilobites of Ohio 

 (see p. 4 for use of keys) 



1. a) Tail shield not segmented externally Isotelus 



b) Tail shield segmented externally 2 



2 . a) With cheek spines 3 



b) Without cheek or tail spines Calymene 



3. a) Head shield with a broad brim, covered with coarse pits Cryptolithus 



b) Head shield narrow, not pitted 4 



4. a) Tail shield with two long spines Ceraurus 



b) Tail shield with three pairs of short, blunt spines Ceraurinus 



