EXPLANATION OF PLATE XXI. 



Ptychodera hedleyi, sp. nov. 



Fig. 9. Transverse section through the branchial region ; on the left side 

 a gill septum (gs.) is shown, and on the right a gill tongue 

 (gt.} x 30. 



10. Sagittal section through two gill septa and the gill tongue 

 between, x 135. 



[For Reference Letters see pages 345-6. 



