OF THE SPONGIAD^E. 199 



the skeleton is so abundant as to cause it to simulate a 

 delicate form of Chalina, but on immersion in Canada 

 balsam the fibre-like form disappears, the sarcode con- 

 tracting into a mere granulated coating, and the skeleton 

 assumes the normal appearance of Isodictya. Tig. 370, 

 Plate XXXVI, represents a section at right angles to the 

 surface from Isodictya Normani, exhibiting the regular and 

 nearly rectangular structure of the network of the skeleton, 

 X 108 linear. 



SPONGILLA, Linnteus, Lamarck, and Johnston. 



HALICHONDRIA, Fleming. 



The structural peculiarities of the skeleton of Spongitta 

 are the same as those of Isodictya, and if there had not 

 existed a striking distinctive difference in their reproductive 

 organs the two genera must have been united. Under 

 these circumstances I propose the following as the characters 

 of the genus Spongilla. 



Skeleton without fibre, composed of a symmetrical network 

 of spicula ; the primary lines of the skeleton passing 

 from the base or centre to the surface, and the 

 secondary lines disposed at about right angles to the 

 primary ones. Reproductive organs, ovaries, coriaceous 

 and abundantly spiculous. 



Type, SpongillajliwiatiliS) Linnaeus. 



All the species are inhabitants of fresh water. As an 

 illustration of the form of the skeleton in this genus, see 

 the figure of that of Isodictya Normani, Fig. 376, Plate 

 XXXVI. 



In some species from the River Amazon, the skeleton 

 fibre is so abundantly spiculous as to cause it closely to 

 simulate that of a Desmacidon ; but a careful observation 

 of the more slender portions of the skeleton will dispel this 

 illusion. 



