OF THE SPONGIAD^!. 211 



usually consists of a series of single grains, but occasionally 

 we find two or three compressed together. In some genera 

 belonging to this suborder the arenation of the fibres is 

 confined to the primary or radial ones, and the secondary 

 system of fibres are destitute of extraneous matters. In 

 other genera they occur occasionally in the secondary 

 system as well as in the primary one. In Stematumenia 

 the primary fibres are frequently somewhat compressed, 

 and are abundantly arenated. The smaller or secondary 

 series of fibres are usually cylindrical, and most frequently 

 without either grains of sand or spicula. Several of the 

 common Bahama sponges of commerce belong to this sub- 

 order, but the best type is the genus Stematumenia, 

 described by me in the ' Annals and Magazine of Natural 

 History 3 for December, 1845, vol. xvi, p. 40G, plate xiv, 

 figs. 1, 2. The genus may be characterised as follows : 



STEMATUMENIA, Bowerbank. 



Skeleton. Primary fibres solid, more or less compressed, 

 containing a central axial line of spicula and grains of 

 extraneous matters. Interstitial structures abundantly 

 fibro-membranous. 



Fig. 256, Plate XII, represents the fibro-membranous 

 tissue from the dermal membrane of a species of Stematu- 

 mema. The fibres are disposed without order, X 1 83 

 linear ; and Fig. 381, Plate XXXVII, a portion of a Stema- 

 tumenia exhibiting the skeleton fibres with the axial line of 

 sand and other extraneous matters, and the fibro-mem- 

 branous tissue in situ, X 175 linear. 



Suborder VII. Irregularly and entirely areno-fibrous 

 skeletons. 



Types, Dijsidea fragitis, Johnston. 

 Dysidea Kirkii, Bowerbank. 



The peculiarity of this suborder is that the fibre of the 



