XU INTRODUCTION. 



the foUowiug would be the order in which we should 

 have to dispose of them. 



Our genus Hymeniacidon would receive the follow- 

 ing very discrepant genera Taguilla, Tapiliata, and 

 Suberites. 



Halichondria will contain Reniera and Axinella. 



Isodictya would receive Eeniera, Axinella, Stegilla, 

 and Oribrella. Desmacidon will receive a Reniera, 

 Spongia would receive a Cacospongia, Spongelia, and 

 Barcotragus. 



Pachymatisma will receive Stelletta, Caminus would 

 be referable to Pachymatisma, Verongia receives Caco- 

 spongia, Guminaj and Aplysina. 



With this distribution of species with, apparently, no 

 well-defined genera to receive them, it would scarcely 

 be possible for any student to follow Professor 

 Schmidt's description of his species of Adriatic sponges 

 with any probability of identifying them. 



If all these numerous discrepancies in the assign- 

 ment of species to genera occur in thirty-three species 

 examined, we may well imagine the confusion that 

 would arise from the examination of the whole of Dr. 

 Schmidt's Adriatic species of sponges. 



The great amount of discrepancy and indetermi- 

 nation exhibited by the comparisons of the systems of 

 Nardo and Schmidt, with that of the arrangement in 

 accordance with anatomical structure, renders a further 

 description of the princiioles of arrangement adopted 

 in this work necessary to the full and complete com- 

 prehension of the mode adopted to arrive at a success- 

 ful determination of genera and species. 



The difference of the systems of arrangement pro- 

 posed by Professor 0. Schmidt, and that adopted in 

 this work is — that the genei-a, in the former case, are 

 based principally on form and external characters, while 

 in the latter they are founded purely on anatomical 

 structure. 



I have always behoved that it is, not that nature 



