Structure in the Devonian Limestone, de. 413 
is hexactinellid, not formed of a convoluted fibre like that of 
Stromatopora, and there is but one kind of pore on the surface, 
viz. that of the vertical lines, not two sizes as in Stromatopora, 
while the tubular lines are without tabule as just noticed; at 
least this is the type to which I allude. 
Here it might be mentioned that there are two distinct features 
in Stromatopora which distinguish it from sponges: viz., 1st, 
the vertical tubes in Stromatopora, being for the full-grown 
polyps, are of the same size throughout, while all the tubes of 
a sponge, being parts of the excretory canal system, continue 
increasing in size from a mere point to their termination in 
the oscule or vent ; and, 2nd, the vertical tubes in Stromato- 
pora are interrupted by tabule or transverse septa, which do 
not exist in the excretory canals of the sponge. Thus, as I 
have before stated, Stromatopora more nearly resembles Tudi- 
pora musica, but most of all MWillepora alcicornis ; while the 
hexactinellid structure to which I have above alluded is more 
like that of the fossil hexactinellid sponges—to wit, Verruco- 
celia gregaria, Zitt. 
Doubtless in the Devonian Limestone (which may be said 
to be one mass of corals, of course including the Stromatopore, 
particularly near Newton-Abbot, where Mr. Vicary tells me 
there is a quarry in which not a fragment as large as a man’s 
fist can be found without containing one or more species dis- 
tinctly and beautifully differentiated, and therefore originally 
was probably a coral reef) there were also sponges possessing 
the hexactinellid structure above mentioned, unless the latter 
belonged to something else ; but, be this as it may, thin slices 
alone will not decide the question, which can only be deter- 
mined by the possession of a whole form for dissection. 
Doubtless, too, there are gradationary forms which link the 
Actinozoa to the Hydrozoa ; and these may be accompanied by 
their respective coralla; so that it must not always be laid 
down that because the corallum is like that of an Actinozoon 
it must necessarily have been one, or vice versd. To prove 
that this hexactinellid structure was a sponge it would be 
necessary to show that it possessed spicules, or at least an 
excretory canal-system like that of sponges, which can only 
be done by sectioning an entire specimen, such as Mr. Vicary 
kindly gave me of Stromatopora for comparison with Mille- 
pora alcicornis. 
Pursuing the subject of extinct Hydrozoa still further, I find 
among Dr. Bowerbank’s collections several kinds of fossils 
labelled “ Flamborough-Chalk Sponges,” chiefly composed of 
chalcedony with a little chalk here and there, viz. :—No. 1. 
Subglobular, about the size and shape of a walnut, 1 inch in 
