238 AETHUE DENDT. 



Lelapia australis is extremely rare, and although Mr. 

 Wilson has for some years past sent me the results of his 

 dredging expeditions, so far as the sponges are concerned, I 

 have never yet had the good fortune to meet with a specimen. 



Genus 12. — Leucyssa, Haeckel (5). 



Diagnosis. — Canal system presumably of the Leuconoid 

 type. Skeleton composed solely of oxeote spicules irregularly 

 scattered through the sponge. 



Remarks. — This is another of those genera of which we 

 know scarcely anything but the skeleton with any degree of 

 accuracy. There can, however, be little doubt that the canal 

 system belongs to the Leuconoid type. The fact that Haeckel 

 included the genus amongst his Leucones, and the irregular 

 character of the skeleton, both point to this conclusion. I 

 have already discussed the relationship of the genus in speak- 

 ing of the skeleton. For the present it may perhaps best be 

 regarded as derived from a Leucandra-like type by loss of 

 the radiate spicules, and their replacement by oxea. There are 

 three very distinct species included by Haeckel (5) in the genus, 

 viz. Leucyssa spongilla, L. cretacea, and L. incrustans. 

 All these species are extremely rare, so that the probabilities 

 of our obtaining a more exact knowledge of the canal system 

 of the genus are somewhat remote. 



Family 4. — Heteropid^, Dendy (4). 



Diagnosis, — There is a distinct and continuous dermal 

 cortex covering over the chamber layer, and pierced by in- 

 halant pores. Subdermal sagittal triradiates are present. 

 The flagellated chambers vary from elongated and radial to 

 spherical and irregularly scattered. An articulate tubar 

 skeleton may or may not be present. 



Remarks. — The leading characteristic of this family, by 

 which it is distinguished from all others, is the presence of the 

 subdermal sagittal triradiate spicules, which, to a greater or 

 less extent, replace the primitive articulate tubar skeleton. 

 As regards the canal system, we meet with much the same 



