564 DR. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Nov. 2, 
the external surface of the sponge, but they occur in considerable 
numbers on the more deeply situated portions of the skeleton-fibres, 
whence they are projected into the areas of the skeleton-rete. They 
vary considerably in the amount of their development : some are 
comparatively short, and have their lateral radii widely spread ; and 
these are abundantly spinous; while others are taller and have 
slender and nearly smooth radii. The dimensions of one of the 
stouter forms was 51, inch high, with a lateral spread of 34,5 inch. 
There is no species among those whch are most nearly allied to 
the one in course of description with which it is likely to be econ- 
founded. ‘The robust form of its skeleton, aud the peculiarities 
of its membranes and its other organs strikingly distinguish the 
species. 
The abundance and variety of the forms of defensive spicula in 
this sponge present a striking evidence of the futility of attempting 
to arrange the Spongiadz by the forms of their auxiliary spicula, ag 
it has been suggested by some imaginative naturalists. Systems 
founded on such bases look very learned and imposing upon paper, 
but when applied to the accurate discrimination of species they 
prove quite inadequate to their proposed purpose. 
In such sponges as the one under consideration, which have 
exceedingly thin parietes, and but comparatively small portions of 
soft tissues, it becomes necessary that those vital parts should be 
taken especial care of ; and hence the profusion and variety of these 
minute defensive spicula to protect the vital parts, otherwise so 
much exposed to the numerous minute predatory creatures that 
exist so abundantly around them; and hence it is that nature has in 
each case provided the defences most suitable to the various species, 
without reference to any particular type of sponges, and those only 
most appropriate to the purpose of the preservation of the mem- 
branous and sarcodous organs so essential to the individual’s exist- 
ence. In the species in course of description, we have not only the 
usual rectangulate sexradiate organs of defence common to so 
many siliceo-fibrous sponges, but we also have, in addition to them, 
those which are so frequently appropriated to Halichondria and 
many other genera differing widely in their structures from each 
other, to render the preservation of the delicate membranous organs 
of this species completely certain. In other species of siliceo- fibrous 
spouges of similarly delicate structure we have the floricomo-sexradi- 
ate stellate forms, as in Farrea spinulenta, which are so plentiful in 
several species of Geodia, a genus differing widely in its structural 
peculiarities from Farrea and other kindred genera. 
A slight doubt exists as to the true locality of this sponge, which 
the decease of my late friend Mr. Henry Deane does not allow us to 
clear up. When Captain Tyler received the specimen from Mr. 
Deane, he received others of a similar description from the coast of 
Tripoli; but he is strongly of opinion that this species was among 
those that were brought up on the cable by Captain Hunter in lat. 
14° 8'N,, long. 77° 38’ W. from 800 to 1000 fathoms depth. 
