EXPLANATIONS OF PLALE IV, continned. 

 Callograptus' eleqans. 



Fig. 15. An enlargement of the noncelluliferous side of a bifurcating branchlet, show- 

 ing the striated surface and a semiarticulate structure. 



Ptilograptus plumosus. 

 Fig. 16. A fragment which is three times branched. 



Ptilograptus geinitzianus. 



Fig. 17. A fragment which is irregularly branched, showing the noncelluliferous side. 

 " 18. An enlargement showing the cell-apertures. . 



