EXPLANATION OF PLATE XI. 



Fig. 1.- Axis of Isis hippitris, Linnaeus. Photograph of a 

 specimen 9 cm. in height, from Murray Island, 

 Torres Strait. 



Fig. 2. Basal portion of Plumardla australis, sp. nov. 

 Photograph of a specimen 24- 7cm. in height, from 

 fifty miles south of Cape Wiles, South Australia, 

 75 fathoms. 



