Knowledge of the Spongida. 245 
Salterton, South Devon, where I reside (Nos. 19 and 20, 
pp. 315 and 433 respectively). 
As regards H. Dujardinit, nothing can be better than 
Johnston’s description and generic diagnosis, excepting that 
he did not see any ova. They are abundantly present, how- 
ever (though not far advanced), in the specimens which I 
have just now (28th June) taken off the rocks, while the 
more minute histology of the species was described in 1874 
(loc. ctt.). 
When fresh and én setw the yellow transparent colour and 
oily appearance of Hymeniacidon Dujardin and Halisarca 
Duwardinit ave so much alike that it is almost impossible to 
distinguish them from one another without microscopic exa- 
mination, when the presence of the spicules in the former, with- 
out any thing else, is quite sufficient. It is therefore not 
extraordinary that Dr. Bowerbank so far, should h7cmself 
have made the mistake to which J have alluded. 
Halisarca Dujardinii not only differs trom HH. lobularis 
when observed in sttu by shape and colour, the former pre- 
senting an even surface with a yellowish transparent colour 
like oil or albumen (“ white of egg”? uncooked), and the latter 
a lobulated surface with a bluish carmine colour, especially 
over the more prominent parts, but, when examined under 
the microscope, A. Dujardinii is found to consist of a massive 
structure permeated by an excretory canal-system that has 
generally only one (but may have more) short tubular vents 
projecting from the surface, which is otherwise entirely covered. 
by a smooth epidermis or dermal layer of sareode (cuticula). 
On the other hand, /. lobularis is made up of contorted ana- 
stomosing knotted tubulation, with intervals (lacune) between 
the convolutions like those of Grantia clathrus, Sdt.,= Clath- 
rina, Gray, = Ascetia clathrus, Hickel (No. 15, vol. 11. p. 30, 
Taf. 4), opening here and there, by the union of two or more 
convolutions, in common vents (No. 26, Taf. 1. figs. 6 and 7) ; 
so that there is an excretory canal-system, as usual, together 
with the spongozoa in groups (ampullaceous sacs), and other 
sponge-elements zmside the tubulation, and an external one, 
apparently produced by cilia, on the outside, which may thus 
keep up a circulation of water throughout its lacunose or 
reticulated mass. The latter has been called by Hiickel the 
“intercanal system’? (No. 15, vol. i. p. 275); but I have not 
been able to observe, under the most favourable circumstances, 
any cilia on the surface of the tubulation in Clathrina (which 
is abundant here) ; while, from the dermal layer of cells in 
reserved-in-spirit specimens of A. Dujardinii being so like 
that of H, lobularis, 1 think the former, if examined in the 
