1875. ] DR. J. S. BOWERBANK ON THE SPONGIADE. 285 
The tricurvate acerate tension-spicula are also very small and slender ; 
one of the largest of them measured =4, inch in length: the curves 
of these spicula are not very strongly produced, and some of them 
exhibit but faint traces of curvature ; they are not very numerous. 
The retentive spicula are especially remarkable for the great variety 
of their size and form. The largest of the retentive spicula, the 
inequidentato-palmate anchorate ones, are congregated in rosette- 
shaped groups, a few only appearing singly located. The groups of 
these spicula so characteristic of the genus Raphiodesma are not 
very numerous, nor do they contain so many spicula as those we 
observe in some other species of the genus; the usual number is 
about eight or ten in each. They are situated on the basal mem- 
brane as well as on the inner surface of the dermal one, just as simi- 
lar groups of such spicula are dispersed on the inner surface of our 
British species R. lingua, in which they are frequently crowded 
together in considerable numbers. The spicula in the species in 
course of description are strongly produced ; an average-sized one 
measured 1, inch in length, and the breadth of the broad spatulate 
distal end was ;,/;, inch. These dimensions contrast strongly with 
those of the numerous small inequipalmate anchorate ones dispersed 
on the surface of the membranes, the average length of which is ~),, 
inch; and the contrast is still greater with the yery minute palmato- 
equianchorate ones, two of which measured respectively 5,5 and 
3050 inch in length ; so that a considerable number of the latter ones 
might be shovelled up as in a scoop by one of the large form of these 
spicula which compose the large rosette-like groups. One of the 
stout bidentate equianchorate spicula measured ;4; inch in length. A 
similar difference in size occurs between the two sorts of bihamate 
spicula. The larger of the two measured =}, inch in length, with 
greatest diameter of the shaft ~,; inch, while the length of one of 
the smaller description of this form was +=4,5 inch. 
The fasciculation of the skeleton is very variable ; some of the 
bundles contain numerous spicula, while others consist of two or 
three only; and the mode of disposition of the fasciculi is also very 
irregular. The spicula in all the bundles appear to have their bases 
and apices coincident. The length of an average-sized skeleton- 
spiculum is =; inch, and the diameter 5,457 inch. 
The basal membrane is abundantly armed with numerous attenuato- 
acuate entirely spined internal defensive spicula projected at right 
angles to its inner surface. In the basal portion of the sponge a 
thin stem of a Tubularia was imbedded ; and this was closely sur- 
rounded by basal membrane, from all parts of which numerous 
internal defensive spicula were projected. This curious habit of the 
sponge to surround included extraneous matters with membrane, and 
then to project defensive spicula from their surfaces, I have several 
times observed in some of our British sponges. 
On the surface of another sponge from the same locality I found 
a very young specimen of the sponge under description not exceed- 
ing a of an inch in diameter and as thin asa piece of paper. The 
dermal membrane was in a fully developed condition; the basal 
