136 ARTHUR DENDY. 
modification perhaps even more remarkable in my Gran- 
tiopsis cylindrica (1). 
As I have previously pointed out, the arrangement of the 
skeleton in the Calcarea Heterocela is of more importance 
for purposes of classification than the mere form of the com- 
ponent spicules, and the difficulty lies in explaining how the 
very peculiarly arranged skeleton of Lelapia can have 
been derived from a Syconoid ancestor with its characteristic 
articulate tubar skeleton. 
We may, however, at once confine our attention to the 
skeleton of the chamber-bearing layer, for that of the dermal 
and gastral cortex differs in no essential points from the corre- 
sponding parts in other corticate Heterocela. Taking first the 
subgastral sagittal triradiates, we find in these a strong argu- 
ment in favour of our view, for they exactly correspond to 
the similar spicules of the typical articulate skeleton. These 
spicules, indeed, seem to be wonderfully persistent, being also 
met with, as I have already pointed out, in the genus Leu- 
candra, after all other traces of the articulate tubar skeleton 
have disappeared. 
The huge oxeote spicules are probably, like the very similar 
spicules of some species of Leucandra (e. g. L. cataphracta, 
Haeckel), to be regarded as incursions from the dermal cortex, 
the dermal surface being the characteristic position for oxeote 
spicules. 
We have left the spicular fibres, whose presence distinguishes 
Lelapia australis from all other known recent sponges. 
These I believe to be derived from the articulate tubar skeleton 
of a Syconoid ancestor. The arguments in favour of this view 
are as follows:—(1) The position of these spicules with regard 
to one another is the same as in the typical articulate tubar 
skeleton, i. e. with their basal rays parallel, overlapping, and 
all pointing in the same direction. (2) The position of the 
spicules with regard to the gastral and dermal surfaces is, 
when the position of the fibre as a whole allows of it, almost 
invariably the same as in the articulate tubar skeleton, i.e. 
with the basal rays pointing to the dermal surface. (3) The 
