1905. ] SPONGE CLATHRINA CONTORTA. 19 
identity of contorta and spinosa, it is hardly necessary for me to 
express my opinion with regard to those systems of classification 
which define not only species but even genera of Ascons by the 
presence or absence of monaxon spicules. Before such a character 
as the presence or absence of monaxons can be used for systematic 
Text-fig. 6. 
Abnormal gigantic spicules of the class of the monaxons from a specimen of Clathrina 
contorta from Banyuls (Topsent 12¢). Magnified about 150 lincar (i. e. half as 
much as the spicules figured in text-figg. 2-5), 
purposes, it is necessary to understand clearly what is meant by a 
monaxon spicule. In calcareous sponges a spicule of this class may 
be one of two perfectly distinct things. It may be, on the one hand, 
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