274 THE APODID^: PART II 



No one can study the beautiful plates in Jones and 

 Woodward's monograph of Palaeozoic Phyllopods 

 without being convinced that the forms represented 

 were nearly related to the Apodidae. This first 

 impression is fully borne out when we come to examine 

 the forms more closely. We find several striking 

 characteristics of the Apodidae, which convince us that 

 we really have here to do with animals at least closely 

 related to and easily derivable from Apus. 



FIG. 63. Hymenocaris vermicauda Salter. Upper Cambrian. To be compared 

 with Apus (from Zittel). 



Hymenocaris has a simple flat shield and a terminal 

 segment carrying a long caudal plate, and three 

 visible anal cirri. From the arrangement of these cirri 

 we may safely conclude that there was a fourth 

 hidden behind the caudal plate. It will be remem- 

 bered that we found it necessary to assume that the 

 original Crustacean-Annelid had four anal cirri, two 

 of which were preserved in Apus, while the two others 

 became rudimentary. This assumption certainly re- 

 ceives some support from the fossil under discussion. 



