74 PALEOZOIC FISHES OF NORTH AMERICA. 
dorsomedian plate is so nearly that of the same plate in Pterichthys Milleri, 
that if it were not for this peculiar tuberculation we might conclude that 
we had in this fish nothing more than a huge Pterichthys. 
The margins of the plate under consideration are beveled off and 
straightened in such a way as to prove that it articulated with others, and 
there is no reason to doubt that it formed part of a carapace similar to that 
of Pterichthys. 
Fig. 3 represents the dorsomedian plate of Aspidichthys very much 
reduced; Fig. 4 a portion of the same, natural size. 
