Figs. 138-144- — Mandibles of Arthrodirans : Cleveland Shale, Ohio. 138. 

 Mylostoma variabilis, Newb., visceral aspect. 139. Titanichthys clarki, Newb., 

 visceral aspect. X \. 140. Trachosteus, Newb., outer aspect. X \. 141. Diplo- 

 gnathus, Newb., outer aspect. X \. 142. Diplognathus, seen from dorsal side. 

 143. Diplognathus, visceral aspect. 144. Ditiichthys intertnedius, outer aspect. X 2. 



137 



