234 Proceedings of the Royal Physical Society. 
The description of H. ventilahrum given by Dr Fleming 
in his " History of British Animals" is so accurate and com- 
plete, that it is quoted by Dr Johnston, when treating of 
the same species, in his " History of British Sponges." 
Dr Fleming describes it "as extremely variable in form, 
forming an entire cup, becoming shallower with age, of up- 
wards of a foot in diameter ; or with a cup divided into 
irregular lobes at the margin, or split, and exhibiting a fan- 
shaped leaf; the base, by which it adheres to stones, is solid, 
and the stem is very short ; the substance is thick at the 
base, becoming thinner towards the margin ; when old, the 
central part thickens, becomes reticular, with a brittle ex- 
terior covering, which may be rubbed off, leaving a skeleton 
not unlike some Qorgonice, ; the pores are of various sizes, 
those on the inside of the cup or leaf are larger and less 
angular than the external ones ; the spicula are numerous 
and much matted; the gelatinous matter abounds in the 
young portions, especially towards the margins, and produces 
a cracked surface when drying." 
The other species, belonging to the natural family of 
Spongiadce, also vary extremely in size and shape, according 
to the difference of locality and conditions of temperature 
where they are found. I have here specimens of Halichon- 
dria infundihuliformis^ from Zetland, that differ greatly in 
size and form. These examples prove how unsatisfactory 
any classification would be that was based upon external 
form alone. Nevertheless, Lamarck, in the second edition 
of " An. S. Vert.," includes 138 species in the genus Spongia^ 
without regard to internal organisation, and divides them 
into groups according to external form, which he also chiefly 
employs to distinguish the species. 
As to what has lately been done, and is doing to elucidate 
this difficult and somewhat obscure branch of natural history, 
I will read a few extracts from letters received from my 
friend Dr J. S. Bowerbank, undoubtedly our best authority 
on this subject ; and conclude with a short notice of his pro- 
posed mode of treatment and arrangement, as set forth in a 
valuable paper lately published in the "Philosophical Trans- 
actions of the Koyal Society of London." In October 1855, Dr 
