58 EXTINCT MONSTERS 
the world’s history known as the Silurian and the Old Red 
Sandstone periods. As far as we know, they did not survive 
beyond the succeeding period, known as the Carboniferous. 
1 The student should consult Dr. Henry Woodward’s valuable Monograph 
of the British Merostomata (Paleontographical Society), to which the writer is 
much indebted. With regard to the representation of Pferygotus anglicus in 
Plate IL., it has been pointed out by Dr. Woodward that the creature was unable 
to bend its body into such a position as is shown there. As in a modern 
lobster or shrimp, there were certain overlapping plates in the rings, or 
segments, of the body, which prevented movement from side to side, and 
only allowed of a vertical movement. 
