54 



OHIO FOSSILS 



Fig. 76 



Species of Isotelus have nearly smooth head and tail shields 

 which are not segmented externally. I. maximus is large, up to more 

 than 2 feet long; I. gigas (fig. 76) is smaller and proportionately wider 

 Both are found in all Cincinnatian formations. 



la the following species , the tail shield is segmented and the 

 glabella (central part of the head shield) is distinct. The species can 

 be identified by the presence and position of spines or their absence 

 and the character of the glabella. 



Ceraurus pleurexanthemus bears two long spines on the tail 

 shield; the glabella has 4 lobes on each side ; there is a prominent 

 cheek spine and each thoracic segment ends in a spine on each side; 

 it is a Trenton species. 



Ceraurinus icarus (fig. 77) also has a 4-lobed glabella, short 

 cheek spines close to the body, and a tail shield with 3 pairs of short, 

 blunt spines; it is found in the Richmond. 



Cryptolithus tesselatus (fig. 78) of the Eden is 

 distinguished by the broad brim of the head shield 

 which is covered with coarse pits ; it has a long 

 cheek spine on each side. 



Fig. 78 



Fig. 77 



Calymene meeki (fig. 79) has neither cheek 

 nor tail spines and the brim of its head shield is 

 narrow and not pitted; the glabella is distinct and has 2 deep lateral 

 grooves; it is found in all Cincinnatian formations. Calymene gran - 

 ulosa is smaller than C_. meeki and has coarse granules, like pim- 

 ples, all over the surface of the body. 



EDRIOASTEROIDEA . Several kinds of seat-stars are found 

 in the Ordovician of Ohio, but most of them are very rare. One of 

 the least rare is Agelacrinites cincinnatiensis of the McMillan for- 

 mation; it looks like a starfish sitting on a cushion made of scales; 

 the whole thing is really a single animal. 



CRINOIDEA. Crinoids are abundant in the Ordovician but perfect specimens are seldom 

 found. On the other hand, there is scarcely a formation in which crinoid stems and joints are 

 not abundant. Crinoids of various types are illustrated elsewhere in this book. Specimens in 

 which the cup and arms are preserved should be referred to a professional for identification. 

 No Ordovician crinoid is common enough in Ohio to deserve description here. 



STELLEROIDEA . Several species of star- 

 fish have been described from our Ordovician rocks 

 They are so rare that finding one is a major event 

 in a collector's life. Specimens should be referred 

 to a specialist for identification. 



GRAPTOZOA. Graptolites are found, though 

 rarely, in our Ordovician rocks. An example is 

 Climacograptus typicalis of the Eden, which looks 

 like a tiny saw, but with square teeth, and is black 

 in color. 



