Vlll INTEODUCTION. 



purpose of the authors of such systems with com- 

 paratively few species to describe, but they can never 

 convey correct information to the minds of their pupils 

 and followers in an extensive course of studies. On the 

 contrary, if we base our genera on the skeleton struc- 

 tures of the sponges, in accordance with the systems 

 generally adopted by naturalists in their arrangements 

 of the higher classes of the Animal Kingdom we have 

 a permanent and invariable source of generic charac- 

 ters, however variable the species or individuals may 

 be in size, form, or stage of development, so that the 

 genus may be readily determined by even a minute 

 fragment of the subject under consideration. 



With these preliminary observations we will now 

 compare the results of my examinations of the 

 Adriatic sponges, presented to me by Professor 

 Schmidt, and named by him in accordance with his 

 own system of arrangement ; with the genera to which 

 they would have been referred according to the 

 system of natural arrangement by means of the 

 anatomical mode of structure of their respective 

 skeletons. 



The following are the results of the microscopical 

 examination of the skeleton structures of the six 

 species of Reniera that I received from Professor 0. 

 Schmidt. 



RENIEKA NARDO. 



R. digita, Schmidt. A Halichondria with rather 

 short acuate spicula. 



R. aquceductus, Schmidt. Halichondria with acerate 

 spicula. 



JR. semitubuloas ? Schmidt. Isodictya spicula acerate. 

 This specimen is in a bad state for examination. 



R. nigrescens, Schmidt. Halichondria with acuate 

 spicula, with a stout and regularly constructed skeleton 

 rete. 



R. palmata, Schmidt. Isodictya with short, stout 

 acerate spicula. A very distinctly developed skeleton. 



