a new Oenus and Species of Monaxonid Sjyonges. 155 



As already stated, the relations of this sponge are undoubt- 

 edly with the Suberitida3, yet it is quite distinct from all 

 previously known species, and we create for it a new genus, 

 which we place near to Polymastia. Probably Prof. Sollas's 

 species Radiella schoenus {= Poly mast ia capitata^ Vosm.), to 

 be mentioned later, comes very close to it. 



By far the most interesting feature in this new sponge is 

 the remarkable grapnel-spicule and its bearing upon questions 

 of classification, more especially upon the relations of the 

 Monaxonida to the Tetractinellida. The upshot of this is 

 that the sponge in question adds a new and very important 

 link to the chain of evidence in favour of supposing the 

 Tetractinellida to be derived from the Monaxonida. The 

 present occasion seems to be a favourable opportunity for 

 summarizing the evidence which has now been accumulated 

 in favour of this view. Professor Sollas has very kindly 

 favoured us with his views on the subject, which have been 

 indicated from time to time in his various papers. One of 

 the most important links is to be found in the genus Tetilla* : — • 

 '"''Tetilla is a genuine though somewhat divergent member of 

 the corticate Choristidaj, with close affinities to the Desmaci- 

 dina; it links together the suborders Tetractinellida and 

 Monaxinellida. The evidence for this statement is found first 

 in its embryological development, next in the characters of 

 the Esperiad Rhaphidotheca Marshall- llalli^ Kent. In the 

 embryo we find some of its tetractinellid spicules in course of 

 development ; they commence with a swelling at the distal 

 end of large uniaxial spicules, from which afterwards teeth 

 are budded off one by one. This is true both for the grapnel- 

 and fork-shaped spicules. Thus the uniaxial clearly precedes 

 the tetractinellid form in development, a fact of signal 

 importance in the discussion as to which originated first, 

 Monaxinellida or Tetractinellida, and in complete correspond- 

 ence with observations made on the order of development of 

 the spicules in the Calcispongiai. 



" In the next place, in lihaphidotheca Marshall-Halli we 

 find the distal ends of some of the large spicules which project 

 from the skeletal fibres beyond the skin distinctly thickened 

 into globular or oval or cylindrical bulbs, in which the axial 



thread ends in a slight spherical expansion The 



rounded swelling of the distal ends of projecting spicules is 

 not confined to Rhaphidotheca ; I have it in a less marked 

 form in a suberite to which I give the name of Radiella 

 schanus [(7-)(plvo<;, a bulrush)." 



Professor Sollas has kindly sent us preparations and 



* Vide Sollas, Ann. & Mag. Nat. Hist. March 1882, p. 162. 



