THE EVIDENCE OF THE CENTRAL NERVOUS SYSTEM 27 
form is Limulus. Crustaceans such as crabs and lobsters are of 
much later origin, and do not occur in any quantity until the late 
Fic. 8.—A, Plerygotus Osiliensis (from Scumipt). B, Stylonurus Logani (from 
Woopwarp). C, Slimonia acuminata (from Woopwarp). 
Mesozoic period. The earliest found, a kind of prawn, occurs in the 
Carboniferous age. 
Korschelt and Heider have accordingly suggested the name 
Paleostraca for this whole group, and Protostraca for the still earlier 
