20 ON THE SPONGE CLATHRINA CONTORTA. [May 2, 
a primary monaxon spicule, derived from a single mother-cell, 
and developing exactly in the same way as a single ray in a tri- 
radiate system, with which it is strictly homologous. It may be, 
on the other hand, a secondary monaxon, derived by modification of 
an entire triradiate system by loss of one ray, perhaps in some cases 
two rays. Good examples of monaxons undoubtedly of secondary 
nature aie the elbowed monaxons in the stalk of Clathrina lacunosa 
Johnston (renamed Ascandra angulata by Lendenfeld). TI believe 
also, as stated above, that the monaxons of contorta are to be regarded 
as secondary. It is clear that a character which is sometimes one 
thing, in other cases quite another thing, cannot be usefully 
employed for purposes of systematic classification, not, at least, 
until more is known about it. 
If Ascetta spinosa be put as a synonym of Clathrina contorta, 
it is seen that the species has a wide range, extending from the 
Adriatic round the coasts of France into the English Channel, and 
probably also on to the coasts of Great Britain. 
Tt is my pleasant duty finally to express my thanks to friends who 
have assisted me in the preparation of this memoir, put together 
from observations for the most part of long standing, at a time 
when the stress of other work, caused by preparations for my 
departure for the Tropics, was very great. My friend Mr. G. R. 
Alford, who is making a special study of the variation of this 
sponge, has given me valuable assistance, as will be evident from 
the facts I have quoted from him above. Mr. Alford has also 
kindly undertaken to see this memoir through the press for me. 
My friend and pupil Mr. L. R. Crawshay has given me great help 
in preparing the illustrations. Finally, I have to thank Monsieur 
Topsent, of Caen, for his kindness in sending me specimens from 
Roscoff and elsewhere and for answering many queries. 
BIBLIOGRAPHY. 
(1) Bowrrsank, J. 8. A Monograph of the British Spongiade, 
London, Ray Society, 3 vols.: 1864-1874. 
(2) Harcken, E. Die Kalkschwimme. Berlin, 1872; 3 vols. 
(3) LeENDENFELD, R. v. Die Spongia der Adria: I. Die Kalk- 
schwimme. Zeitschr. wiss. Zool. li. (1891) pp. 185-321 
361-433, pls. vill.—xv. 
(4) Mincuin. EK. A. Sponges in: Lankester, ‘A Treatise on 
Zoology, London, 1900. 
p) 
Other references are cited in the list of synonymy, p. 17 above. 
EXPLANATION OF PLATE T. 
Clathrina contorta from Banyuls. 
A from above; B from above, and C from the side, to show the oscular 
tubes (O). 
