POLYPLACOPHORA. 



XXV11 



Phylogenetic diagram of the families and subfamilies of 

 Polyplacophora. 



-a 



o 



o 



a 

 ,13 



A 



Q 



Callistoplacinse 



Lepidopleuridse 



A diagram illustrating the phylogeny of the genera of Ischnochi- 

 tonince is given on page 254 ; another illustrating that of the gen- 

 era of Chitonidce is given below ; and the descent of the genera of 

 Acanthochitidce is shown under the head of that family. The 

 mutual relations of the genera included in Callistoplacince are not 

 clear to me and require much further investigation ; but the views 

 expressed on pages 259, 260 may possibly suggest a clue to the 

 super-generic groups. 



