1108 
DE. J. S. BOWEEBANK ON THE ANATOMY 
In the only two specimens of this genus that I have seen, there is a small pebble 
imbedded in the centre of each sponge, from the surface of which the basal fasciculi of 
the radial series emanate ; but although this appears to be the established habit of this 
species, it is advisable not to consider it as a generic character, although it may even- 
tually prove to be that the pebble is as much a portion of the skeleton of the animal 
as the grains of extraneous matter which are taken up by and become imbedded in the 
keratose fibres of the genus Dysidea. Plate LXXIV. figs. 4 & 5. 
Dictyocylindeus, Bowerbank. 
Skeleton without fibre, composed of a loosely compacted columnar axis of spicula, 
disposed principally in the direction of the line of the axial column, from which a 
peripheral system of long single or fasciculated defensive spicula radiate at right 
angles to the axial column. 
Halichondria hispida, Johnston, and Spongia stuposa, var. damicornis, Montagu, are 
excellent types of the peculiar mode of arrangement of the spicula which characterizes 
this genus. The skeleton consists of a central column of large elongate spicula, disposed 
principally in the line of the axis of the sponge and at a slight angle to it, approaching 
in form an irregular cylinder of network of elongated meshes, rarely exhibiting an 
appearance of horny fibre, but formed for the most part of spicula cemented together 
near their terminations. Towards the base of the sponge the horny substance surround- 
ing the spicula is sometimes so thick as to simulate a proper horny fibre ; but if it be 
carefully traced, it will always be found to be dependent on the spicula : where their 
course is abruptly terminated the homy structure also terminates, whereas in true horny 
fibrous structures which contain spicula the course of the fibre is continuous and uni- 
form whether the spicula be present or deficient, and in the newly produced fibre the 
latter is generally the case. 
The structure of the skeleton in this genus differs from that of Halichondria oculata, 
Johnston, or Chalina oculata, Bowerbank, in the regularly elongate disposition of the 
spicula of the skeleton; and the spicula are necessarily very much larger and longer 
than those included in the close fibrous network of H. oculata ; and it is still further 
removed from the horny fibrous structure of Halichondria cervicornis^ Johnston, Hist. 
Brit. Sponges, pi. 4. The axial column of this genus differs strikingly from that of the 
strong closely packed axis of Ecionemia ; and the peripheral 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. Part II. Plate XXIX. fig. 11 ; and Plate 
LXXIII fig. 7. 
Phakellia, 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. 
