186 ANATOMY AND PHYSIOLOGY 



close fibrous network of C. oculata; and it is still further 

 removed from the homy fibrous structure of Halichondria 

 cervicornis, Johnston, ' Hist. Brit. Sponges,' pi. iv. The 

 axial column of this genus difiers strikingly from that of 

 the strong, closely packed axis of Ecionemia, and the peri- 

 pheral system of spicula are never furnished with ternate 

 connecting spicula. All the species of this genus I have 

 hitherto seen are more or less ramous in form. Fig. 

 365, Plate XXXII, represents part of a small branch of 

 Bictyocylindrus rugosus, Bowerbank, exhibiting the radiating 

 structure of the defensive fasciculi, X 50 linear ; a, part of 

 the central axis of spicula. Fig. 366, Plate XXXIII, 

 represents part of a section through the axial column of 

 Bictyocylindrus ramosm, showing the elongo-reticulate 

 structure of the skeleton of the sponge, X 50 linear. 



PhakelliAj Bowerbank. 



Skeleton. Composed of a multitude of primary cylindrical 

 axes, radiating from a common base and ramifying 

 continuously, from which emanate at about right 

 angles, to the axes a secondary series of ramuli, which 

 ramify continuously as they progress towards the 

 surface, but never appear to anastomose. 



Type, Phakellia ventilabrum, Bowerbank. 



I know of no other species, either British or foreign, 

 that possesses the peculiar conformation that distinguishes 

 the sponge that is the type of this genus. The primary 

 cyUndrical axes very closely resemble those of Bictyocylin- 

 drus, but in that genus the spicula radiating from the axes 

 are separate and distinct, each having its proximal end 

 based on the primary cylinders of the skeleton, and its 

 distal one reaching nearly to, or passing through the 

 dermal membrane of the sponge ; or if they be fasciculated, 

 the fasciculi are simply plumose, and in no case with which 

 I am acquainted at all ramulous. In Phakellia the secon- 

 dary skeleton is formed of distinct slender branches, each 



