86 DR.J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, 
form from circular to oval, and occasionally they are nearly oblong. 
They are protected from the incursions of minute annelids and other 
enemies by the projection into their areas of the fureated termina- 
tions of the skeleton-fibres of the surface-tissues (Plate IV. fig. 2). 
This beautiful mode of defence is very characteristic of the species, 
and is an excellent substitute for the usual defensive spicula in such 
organs. Beside this mode of defence, the dermal surface is fur- 
nished rather abundantly with long slender flexuous spicula, which 
pass over the inhalant areas in various directions. 
The oscular surface of the sponge is not furnished with the same 
minute slender acerate spicula that abound on the inhalant one, but 
the whole of the former surface is protected by a modification of the 
style of defence that is so beautifully exhibited on the margins of 
the inhalant areas. The oscular membrane which closes that organ 
and the slightly elevated ring whence it proceeds have not the same 
furcated defences that are so abundant at the margins of the inha- 
lant areas; but as we focus downward through the orifice towards 
the surface of the rigid skeleton of the sponge, we occasionally ob- 
serve some of the furcated defences projecting from the parietes of 
the cavities. The oscular membranes at several of these orifices 
were ina semicontracted state; numerous minute grains of sand 
were scattered on their external surfaces, but no spicula were appa- 
rent in any of the membranes. In one of them the margin was in a 
very perfect condition, slightly thickened ; and the membrane exhi- 
bited faint concentric lines of contraction (Plate IV. fig. 3). 
The dermal membrane is pellucid, and is furnished with a fine but 
very irregular network or stratum of slender siliceous fibres, their sili- 
ceous structure being well characterized by the frequency of their frac- 
tures at right angles to their axes ; they do not appear to anastomose, 
but to overlie each other without any approach to symmetry in the 
mode of their disposition. Plate IV. fig. 4 represents a small por- 
tion of this tissue beneath a power of 308 linear. 
The skeleton-tissue is exceedingly irregular and intricate. The 
fibres of which it is composed are more or less compressed ; they 
are quite smooth, but frequently throw off short branches which 
terminate with crowded masses of minute ramifications of siliceous 
structure. 
In July 1861, when I first saw this sponge in the collection of the 
Jardin des Plantes at Paris, the late Professor Valenciennes told me 
that he had not yet described it; and on the occasion of my last 
visit to Paris, in May 1868, I could not learn that he had subsequently 
done so. I am therefore quite ignorant of the characters he would 
have assigned to his genus Coscinospongia ; but as it agrees in the 
structure of its skeleton with Stutchbury’s previously established 
Dactylocalyx, I have assigned it to that genus accordingly. 
DactyLtocaLtyx M*‘AnprRewu, Bowerbank. 
MacAndrewia azorica, Gray, P. Z. 8. 1859, p. 438, plate xv. 
Sponge pedicelled, sinuously cup-shaped. Surface even or 
slightly undulating. Oscula small, evenly dispersed on the inner or 
