309 
I have only been able to examine the opercular apparatus of 
Sert. operculata (Pl. V, figs. 8—10) and Sert. trispinosa (Pl. V, 
figs. 11—15), but the form of the aperture in the above species 
leaves no doubt that: they must be referred to the same genus. 
In Thwjaria bidens Allm. (2.) the aperture seems to be an in- 
verted Odontotheca-aperture, and this species must, therefore, no 
doubt, be referred to a new genus. 
Diphasia (Agassiz) Lev. 
The aperture, which is horizontal or very little oblique, has 
no teeth and is provided with an adcauline sinus in which is 
fixed an opercular membrane with a large free opercular valve. 
The above genus not only comprises most species referred to 
Diphasia but also those belonging to Abietinaria Kirchenpauer, 
a genus based solely on the form of the hydrothecae which have 
been characterized by the author in the following manner: ,,es 
sind flachenfårmige, bauchige, mit ihrer Basis angewachsene Be- 
hålter, deren nach aussen gerichtete Offnung das Ende eines engen, 
mehr oder weniger langen, nach einer Seite geliegenen Halses 
bildet.” Nutting who accepts Abietinaria as an independent 
genus next to Diphasia characterizes it not only by the form of 
its hydrothecae ("more or less bottle-shaped” ) and gonothecae, but 
also by the presence of an adcauline opereulum, while Broch”) 
proposes to divide the genus Diphasia into two subgenera- Eu- 
diphasia and Abietinaria. As both the form of the hydrothecae 
and the structure of the gonothecae are subject to great variation, 
and the same forms of hydrothecae and of gonothecae are found 
in a number of different genera, I cannot regard Abietinaria as a 
distinct genus, and I think that we may, at least provisionally, 
accept Broch's proposition to divide Diphasia into two sub- 
genera or groups. ; 
1) 98. 
18, 
