99 



On the Calcarea. 

 By B. W. Priest. 



{Read March 25th, 1887.) 



It is with some hesitation I bring this paper before you, for two 

 reasons, first, because you might perhaps think that I can talk only 

 of that on: absorbing subject, Sponge, which by-the-bye, has taken 

 naturalists some years to squeeze much information out of, and, 

 secondly, in dealing with this group, the Calcarea, I cannot avoid 

 bringing, on the one hand a little that must be to a certain extent 

 elementary, and on the other hand I am afraid, parts that may 

 seem a little technical and dry. It is rather a difficult matter to 

 collect all the information one would wish, and bring it into a small 

 compass. 



If I have not done the subject justice in the little time that I 

 have at my disposal, I must ask your indulgence for all short- 

 comings. 



The Calcarea, or Calcispongia, are so named in contradistinction 

 to the Kerdtosa and Silicea, on account of their spicules being 

 composed of carbonate of lime. 



They take the forms of tri-radiates, quadri-radiates, and acerate 

 spicules, the tri-radiate being the most characteristic. 



They occur separately immersed and distributed in the soft tissues 

 of the Sponge, never collected into fibres or found anastomosed to 

 form a regular network, as is the case with some of the siliceous 

 sponges. In consequence of this, after dissolution of the organism, 

 the spicules fall apart, and being more or less soluble in sea water, 

 made it doubtful for some time of their being preserved in the fossil 

 state. 



Of the 137 species described by Hseckel, 18 have the spicules 

 exclusively tri-radiate; 44 tri-radiate and quadri-radiate ; 61 

 tri-radiate, quadri-radiate, and acerate ; 8 composed exclusively of 

 quadri-radiates, and only six species have exclusively acerate 

 spicules. 



Journ. Q. M. C, Series II, No. 19. 9 



