REPORT ON THE MONAXONIDA. Ixvii 



echinating spicules is, as we shall proceed to show, quite insufficient to justify such a 

 wide distinction between the two groups as Vosmaer admits. 



We divide the Desmacidonidae into two subfamilies — (1) the Esperellinse, in which the 

 skeleton fibre is not echinated by projecting spicules, and (2) the Ectyonin^e, in which 

 echinating spicules are present. These two subfamilies are, however, by, no means 

 sharply marked off from one another, for we actually have, in the genus Myxilla (placed 

 by Vosmaer as well as by ourselves amongst the Desmacidonidse), both species with and 

 species without the echinating spicules, and these different species are so closely allied 

 that we have found it impossible to separate them generically. This question is again 

 referred to in the systematic portion of the work, under the genus Myxilla, to which we 

 refer the reader for further details. Here then lies the justification, and we think it will 

 prove to be a sufficient one, of the present arrangement. 



It is probable, nay certain, that the first division of the family, the Esperellinae, will 

 require subdivision, and in our opinion it will fall into several very natural groups, but we 

 cannot, in the present work, make such an arrangement, as we have not the necessary 

 time at our disposal for a complete revision of the group. 



The Ectyoninae are a very difficult group to deal with ; most of them are evidently 

 sponges which are developing a strong horny skeleton at the expense of the spicular 

 element, and the poor degree of development exhibited by the spicules makes their 

 classification unusually difficult. Possibly, as held by Mr. Carter, they have some 

 connection with the Axinellidae, but we cannot believe that it is nearly so close a one as 

 he seems to indicate in uniting the Ectyoninae and Axinellidse in one group by them- 

 selves, the " Echinonemata." To our minds their intimate connection with the 

 Esperellinas far outweighs in importance any relationship which may exist in the 

 Axinellid direction, while the presence of a strongly developed horny skeleton is to be 

 connected here, as in the Chalininse, with the fact that they flourish almost exclusively 

 in warm areas. 



We consider the Axinellidse as constituting a family by themselves, which we place 

 at the end of the Halichondrina, and hence after the Ectyoninae and near to the 

 Suberitidae, with which they seem to have striking affinities. These affinities have already 

 been discussed in speaking of the relations of the Halichondrina to the Clavulina, so we 

 shall not dwell upon them in this place. The family is a very difficult one to deal with, 

 and our knowledge of it is in a most unsatisfactory condition. Its most striking positive 

 character, and that in which it most nearly approaches the Ectyoninae, is the arrangement 

 of the spicules to form the skeleton-fibre ; but though there is a strong superficial resem- 

 blance between the two groups in this respect, yet the arrangement is in reality very 

 distinct in the two cases, for in the Axinellidse all the spicules have their apices projecting 

 very obliquely outwards and forwards from the centre of the fibre, while in the Ectyoninas 

 there is a central core of longitudinally placed spicules cemented together by homy 



