1869.] DR. J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 95 
M°Andrewii, with those representing the organization of D. Bower- 
bankit in Plate VI. figs. 6, 7, 8. 
The form of the sponge under consideration is that of a shallow 
cup with expansively undulating margin. The diameter varies 
from twelve to fourteen inches, and its thickness from half to very 
nearly one inch. It has six large sinuous doublings of its margin, 
which extend as much beyond the general plane of the sponge at its 
under as at its upper surface ; two of these foldings of its substance 
have met at its under surface, and have become cemented together. 
The greater portion of the sinuous margin of the sponge is flat, the 
outer and inner edges in some parts being quite sharply defined. 
The dermal system in this sponge presents very important specific 
characters. In some sections made at right angles to the surface it 
was evidently in a state of complete collapse; the under surfaces of 
the connecting spicula were closely in contact with the surface of the 
rigid skeleton, and their shafts were deeply immersed in its sub- 
stance. ‘This position of the expansile dermai system of the sponge 
is probably its natural one while the animal is in a state of repose. 
The connecting spicula vary considerably in their size, form, and 
degree of development. The primary ternate rays are usually short ; 
and the secondary fureating ones are fiveor six times the length of 
the primary ones, and without any secondary fureations, while at 
other times one or more of the furcating rays have a second terminal 
fureation ; these terminal radii are short, and are frequently pro- 
jected on a plane at right angles to the other furcations; these 
terminal furcations are sometimes very irregular, their apices, 
instead of two only, having three or four small branches projected in 
different directions, as represented by fig. 7, Plate VI. The mode 
of the disposition of the ternate heads of these spicula in the dermis 
is remarkable: they are not arranged so that their ternate radii 
form definite inhalant areas; but the rays cross each other in every 
imaginable direction, and the pores are found in the little irre- 
gular areas, one, or rarely two together, and they therefore appear 
indiscriminately seattered over the whole of the porous surface. 
They are simple orifices without any defensive spicula such as we 
observe in Dactylocalye M°*Andrewii. The dermal membrane is 
abundantly supplied with retentive spicula; they are so numerous 
and closely packed as to completely obscure it. ‘They are very 
minute, and no two are alike in size or form; they require a micro- 
scopical power of about 700 linear to render them distinct to the 
the eye. Under these circumstances they present remarkably thick 
and obtuse proportions, and are distinctly different from any others 
of this class of spicula that I have ever seen. Sometimes the shaft 
is multiangulated, each angle producing a single short cylindrical 
ray, while in other cases the shaft is quite straight, and the radii are 
projected from it in a perfectly irregular manner. Besides these 
two prevailing forms, they assume every imaginable variation of 
shape that such spicula can be subjected to. One of the largest 
and most regular of the multiangulated forms that I measured pre- 
sented the following proportions :—length of spiculum 55 inch; 
