302 E. A. MINCHIN. 
from one another in all those characters which, in my opinion, 
are of fundamental importance for the classification of Cal- 
careous Sponges. I believe that the two families in question 
represent the most deeply-rooted phylogenetic divergence in 
the Calcarea Homoccela, and are two natural systematic 
eroups, one of which—namely, the Leucosoleniid2— 
approaches far nearer to the ordinary Heteroccela, such as 
Sycon, Grantia, Leucandra, etc., than does the other. 
The genus Leucosolenia, Bowerbank, in the sense in which 
the name is employed by me (1905 [2]), constitutes the 
principal, if not the only, genus in the family Leuco- 
soleniide, while the genus Clathrina occupies a similar 
position in the Clathrinide. . 
Having in a former memoir (1898) described the origin 
and growth of the triradiate and quadriradiate spicules in 
various species of Clathrina, it seemed to me important to 
supplement the results then obtained by a study of spicule- 
formation in Leucosolenia. The observations put forward 
here have been carried on, at rather long intervals and with 
many interruptions, over several years, and some of my 
figures are now more than eight years old. I may be allowed 
to mention this in order to explain the relation of my investi- 
gations on calcareous spouge-spicules to those already pub- 
lished by my friend and former pupil, Mr. Woodland. After 
I had observed the principal facts in the development of the 
spicules of Leucosoleniide I suggested to Mr. Woodland 
that he should study the spicule-formation in the Heteroccela ; 
he proceeded to do so in Sycon, and found a mode of origin 
for the spicules in this sponge perfectly similar to what I had 
found in Leucosolenia. I had intended to publish my 
observations a long time ago, but various obstacles and pre- 
occupations prevented my doing so, and in the meantime Mr. 
Woodland’s studies have been published (1905). It is in no way 
with the view of detracting from the value of Mr. Woodland’s 
researches, which he has extended over a wide field, but 
simply in order to protect myself against a possible charge 
of plagiarising from his results that I point out here (as Mr. 
