756 Proceedings of the Royal Irish Academy. 



Brebissonii among the Desmids. The basal disk and capitulum seem 

 to differ in no respect from the typical form, and until some time or 

 other the species can be examined in a living state, this may be re- 

 garded as a variety of the above described form. 



The species I have named after my friend William Archer, P.E. S., 

 so well known for his researches among the lower forms of vegetable and 

 animal life. His researches among the Ehizopods are of such value, 

 that one could wish that he would extend them to animals one step 

 higher in the scale, and so favour science with a series of observations 

 on the sponges. 



The wonderful mimetic resemblance which this new species bears to 

 some of the stages of development of a Crinoidcan scarcely be overlooked. 

 Leaving the texture and composition of the skeleton mass for the mo- 

 ment out of view, and simply looking at its outline — the circular disk- 

 like base — the stem — the profile of which is absolutely the same, except 

 as to size, as that of the pentacrinoid stage of Antedon rosaceus, and 

 the slightly cleft head, the resemblance, to my mind, is very great. 

 Ofcen, indeed, have I been obliged to look, and look again, and to 

 crush down the specimen, before I could convince myself, by a full view 

 of its texture, that I was not deceived. So far as I know, this is a 

 unique case among the sponges, and one is let to wonder what may 

 be the tiny enemies from which Kallispongia Archeri, by this complete 

 disguise, conceals itself. 



