CALCAREOUS SPONGES. 741 



The only known recent species of this genus are : — 



1. P. DEANSii Kirkpatrick. 



Plectroiiinia deansii Kirkpatrick [1911 A]. 



2. P. HiNDEi Kirkpatrick. 



Plectroninia kindei Kirkpatrick [1900 B], 



The type of the genus is F. halli Hinde [1900], a fossil species 

 •from the Eocene of Victoria. 



JFamily 5. MURKAYONID^ nov. 



Murrayoninm Kirkpatrick [1911 A]. 



Diagnosis. Canal system presumably always leuconicl. Skeleton 

 of the chamber layer a rigid calcareous network, not com- 

 posed of spicules. No subgastral sagittal radiates. Dei-mal 

 skeleton composed chiefly of overlapping calcareous scales. 

 Nuclei of collared cells basal. 



This family seems to mark the culminating point of the 

 Leucascid-Leucettid line of evolution, and there is no other 

 known calcareous sponge with a skeleton so highly specialised as 

 Murrayona. 



It is at any rate possible that the aspicular main skeleton of 

 Mtirrayona is derived from the cement-covered fibres of spicules 

 which are known to occur in many of the fossil forms, by a 

 -gradual disappearance of the spicular core, analogous to what we 

 find among the Ohalininre, during the evolution of the group. 

 It is, however, a far cry from the one to the other, and we do not 

 doubt that there are many other ways in which the Murrayonid 

 skeleton may have arisen. 



Genus 14. Murrayona Kirkpati-ick [1910], 



jyiagnosis. "With a definite pore-zone in which the dermal skeleton 

 consists of small triradiates. Tuning-foi^k spicules present 

 beneath the dermal scales. 



For illustrations of this genus see Kirkpatrick [1910]. 



The only known species of this genus is :— 



1. M. PHANOLEPis Kirkpatrick. 



Mitrrayona phanolepis Kirkpatrick [1910]. 



49* 



