281 
That the genus Selaginopsis according to the different manner 
in which it 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, 
belonging to different. genera, and not as Nuttin 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 møre 
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 distinct difference in the structure 
of. the -hydrothecal margin I must put them into two different 
genera. 
"As. Prof. Nutting has come to the incorrect result that the 
characters taken from the opereulum. and the hydrothecal margin 
are inconstant, he has in the systematic arrangement of the Ser- 
tulariidæ committed the same error as most authors,. of laying 
chief stress on the. colonial characters, and if his genera do not 
contain such a beterogeneous assemblage of species.as Schneider's 
groups, it is only because he has paid more attention to the 
strueture 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 Sertulariidae I shall set forth some considerations on the relation 
between the four families Campanudariidae, Lafotidae, Campanu- 
linidae and Sertulariidae in order to define the systematic position 
of the latter. family. 
