BRITISH SPONGIADiE. 9 



1. Halichondria, Fleming. 



Sponge. Skeleton without fibre ; composed of an irregular 

 polyserial network of spicula cemented together by 

 keratode. Vol. I, p. 195. 



Types, Halichondria panicea and incrustans, Johnston. 

 Vol. I, Plate XIX, Figs. 299, 300, 303, and Plate 

 XXXV, Fig. 373. 



2. Hyalonema, Gray. 



Skeleton an indefinite network of siliceous spicula, com- 

 posed of separated elongated fasciculi, reposing on con- 

 tinuous membranes, having the middle of the sponge 

 perforated vertically by an extended spiral fasciculus 

 of single, elongated, and very large spicula, forming 

 the axial skeleton of a columnar cloacal system. Vol. 

 I, p. 195. 



Type, Hyalonema mirabilis, Gray. Vol. I, Plate XXXV, 

 Figs. 374, 375. 



3. Isodictya, Bowerbank. 



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 second- 

 ary lines disposed at about right angles to the primary 

 ones. Propagation by internal, membranaceous, aspi- 

 culous gemmules. Vol. I, p. 197. 



Types, Isodictya palmata and Normani. Vol. I, Plate 

 XXXVI, Fig. 376. 



