281 
That the genus Selaginopsis according to the different manner 
m which lt is understood by different authors contains species with 
two, three or four different forms of opercular apparatus is to my 
opinion a proof that the genus is an artificial assemblage of species, 
belouging to different genera, and not as Nu t tin g means a proof 
that my systematic characters are inconstant. But even if all the 
species contained in the genus were provided with the same form 
of opercular apparatus I should. reject it as unnatural if it were 
based on the chief character, that the hydrothecæ are arranged 
in more than two longitudinal series, as I should reject a Bryozoan 
genus containing for inst. the Caberea- species provided with more 
than two longitudinal series of zooecia. I do not deny that Sel. 
mirabilis and Sel. cylindrica have a very similar habitus because 
of the similar arrangement of the hydrothecæ, but the outer likeness 
ought to have nothing to do with the systematic arrangement, 
and as the two species show a distinet difference in the structure 
of the hydrothecal margin I must put them into two different 
genera. 
As Prof. Nut tin g has come to the incorrect result that the 
characters taken from the operculuin and the hydrothecal margin 
are inconstant, he has in the systematic arrangement of the Ser - 
tularadæ committed the same error as most authors, of Taying 
chief stress on the colonial characters, and if his genera do not 
contain such a heterogeneous assemblage of species as Schneider’s 
groups, it is only because he has paid more attention to the 
structure of the operculum. His best defined genera therefore, are 
Abietinaria and Diphasia , in which the chief character is the ad- 
cauline position of the operculum, while the colonial characters 
used are essentially negative. 
Before proceeding to give definitions of the single genera of 
the Sertularudae I shall set forth some considerations on the relation 
between the four families Campanulariidae, Lafoeidae, Campanu- 
hmdae and Sertularudae in order to define the systematic position 
of the latter family. 
