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their opercula. The colonial form, in the systematic importance 
of which he implicitely believes, gives him in much shorter time 
a general view of the connection between all these forms, showing 
him that the different “groups” are mutually united by transitional 
forms, and that sharp contrasts do not exist at all. The following 
statement, however, seems to show that Schneider uses the 
term “transition” in a very singular manner 1 ): „ Thujaria , Sela- 
ginopsis and Pasythea sind durch Uebergange vermittelt, wie schon 
daraus klar wird, dass Le vinsen Yertreter jeder dieser drei 
Gruppen auf mehrere seiner Gattungen vertheilt.* I cannot see 
the clearness of this argument. When I have shown that the 
species of the old genus Selaginopsis according to their opercular 
apparatus must be distributed irto the genera Thujaria, Sertularia 
and Diphasia, and that other species provided with the same forms 
of opercula are contained within the frame of the old genus Ser¬ 
tularia , this faet does not prove, that Selaginopsis and Sertularia 
are connected by transitions, but only that they are artificial genera. 
On the other hånd theré are numerous transitions between the 
different colonial forms which have been used as generic characters, 
and Schneider, therefore, quite naturally comes to the result 
that all the Sertulariidae strietly speaking must be regarded as 
forming a single genus 1 ). This he again divides into groups ad- 
mitting at the same time that neither are they strietly di vided. 
We shall later consider some of these groups. — i 
While Schneider originally declared that my opercular 
system was quite inconsistent with one based on the arrangement 
of the hydrothecae, he at other places sets forth quite contrary 
statements, according to which we should believe, that there is 
the most complete agreement between the colonial form and the 
structure of the operculum. Thus he savs 2 ). „Aber wenn wir die 
typischsten Formen der Sertularidae ansehen, scheint Hånd in 
Hånd mit besondern Deckelformen auch eine besondere Anordnung 
x ) 54, p. 522. 
2 ) 54, p. 522. 
