DEVONIAN FOSSILS 



89 



Naticonema ( Platyostoma of older publications is like Isonema but 

 has a rounded base and different ornamentation. N. lineata (fig. 2TI) is 

 found in the Columbus and Prout. 



PTEROPODA . The next two genera have been placed in the 

 Pteropoda, a subclass of the Gastropoda. They look more like small 

 cephalopods than snails but they lack septa. They are sometimes found 

 in great abundance on slabs of Devonian limestones and shales in Ohio 

 and elsewhere. 



Fig. 211 



Styliolina is small, conical, and has growth lines but no longitudinal striations. 

 A glance at the figures will separate it from Tentaculites. Styliolina fissurella (fig. 

 212) occurs in the Olentangy, Plum Brook, and Silica. 



Tentaculites is about the size of Styliolina but has distinctive rings on the shell. 

 It looks like a small wood screw but the markings on it are not spiral but circular. 

 T. scalariformis (fig. 213) is found in the Dundee, Columbus, and Delaware; _T. bel - 

 lulus in the Silica. 



CEPHALOPODA. Because of their large size, some cephalopods are bound to 

 attract your attention. They are not as common as corals and brachiopods or even 

 gastropods, so it was difficult to decide which ones to include here and which to leave 

 out. We hope the following key will identify the commoner kinds. Fig 



Key to the Commoner Devonian Cephalopods of Ohio 



( see p. 4 for the use of keys ) 



1. a 

 b 

 c 



2. a 

 b 



3. 

 b 



4. a 

 b 



•o. a 

 b 



6. a 

 b 



7. a 

 b 



8. a 

 b 



9. a 

 b 



Shell straight 2 



Shell curved Acleistoceras 



Shell coiled 5 



Shell straight and smooth 3 



Shell with tubercles or rings , 4 



Septa with wavy edges; shell small, about 1/4 inch in diameter Bactrites 



Septa with straight edges; shell large, more than 1/2 



inch in diameter Ormoceras 



Ornamentation of ring-like expansions and contractions 



of the shell Spyroceras 



Shell smooth except for one row of tubercles lengthwise 



along the shell Tylortooceras 



Whorls touching 6 



Whorls not touching 9 



Umbilicus very narrow, almost closed Tornoceras 



Umbilicus wide 7 



Outer edge of whorl with a row of small tubercles Centroceras 



Outer edge of whorl smooth 8 



Top of whorl with a row of tubercles Nassauoceras 



Entire whorl smooth Gigantoceras 



Whorls expanding slowly Ryticeras 



Whorls expanding quickly Nephriticerina 



