358 Mr. W, J. Sollas on the Genus Catagma. 



not have belonged to a sponge whicli possessed an Hircinian 

 habit, thin shoes of the Upware specimens, which include 

 grains of quartzose sand in the meshes of their network, were 

 examined. As the Hirciniadte do not appear to discriminate in 

 introducing foreign particles into their fibres, but pick up any 

 minute grains which lie upon the sea-floor around them, so one 

 would expect to find some of the quartz grains which occur in 

 the meshes of the Upware sponges also present in the fibre 

 had they possessed any affinities with the Psanimonemata. 

 Such quartz grains might easily be detected by searching with 

 the polariscope ; but a most careful examination failed to dis- 

 cover the least trace of them. Thus we eliminate the Psam- 

 monemata ; and we have next to consider the Pachastrellidaj, 

 to the trifid spicules of which the multiradiates of our sponges 

 offer the closest resemblances. 



In no Pachastrellid sponge, however, so far as I am aware, 

 have we the curved and undulating uniaxial spicules of 

 Catagma, nor is there to be found any definite fibrous struc- 

 ture. Thus we eliminate the Pachastrellidse, the only Tetrac- 

 tinellid group of the Holorhaphidota that is worth considering. 

 Far otherwise is it, however, with the Khaphidonemata. The 

 fibrous structure is not only common, but may be said to be 

 characteristic of a vast number of this kind of sponges ; curved 

 and undulating spicules, very like those of Catag7naj are also 

 very frequent ; and lately 1 have described a unique form 

 {Plectronella iwpillata) in which triradiate and quadriradiate 

 spicules, very similar to those we have been describing, are 

 abundantly present. 



One important difference alone (though certainly that is 

 important enough) divides Catagma from the Phaphidonemata; 

 and that lies in the fact that the echinating multiradiates of 

 the former form the core ot the fibre instead of merely coating 

 its exterior ; but this is no more than the difference which 

 distinguishes the Axinellida from the Ectyonida, the two 

 families of Carter's order Echinonemata ; and there is no 

 difficulty in conceiving that, just as Plectronella presents us 

 with a new departure in the Ectyonida by the substitution of 

 multiradiate for uniaxial echinating spicules, so Catagma may 

 represent a similar departure in the Axinellida. 



This certainly is the view w^hich I feel disposed to take ; and 

 so important does this substitution of multiradiate for biradiate 

 echinating spicules seem to me, that I propose to elevate my 

 group Plectronina to the rank of a subfamily in the Ectyonida, 

 and to make the extinct Catagma the representative of a sub- 

 family in the AxinelHda. The classification would then stand 

 thus : — 



