274 
times being round without teeth and often being curved, with two 
teeth of regular sertularian type. Operculum usually '"composed of 
one flap attached to the abcauline side of margin, but sometimes 
composed of two flaps.” ”"This species appears to break down the 
generic distinctions proposed by Levinsen in that it has both 
a one-flapped and a two-flapped operculum in the same specimens.” 
About the same parts of S. robusta he says: "operculum with two 
flaps on distal portion of branches, often with round margin and 
single abcauline flap on proximal portions.” 
Both in my paper on the regeneration of the Hydrvids 1) and 
in that on the Hydroids from Greenland?) I have pointed out, that 
in the new apertures produced by the regeneration of a hydrotheca 
in a Sertularia the contrast between the thicker and the thinner 
(membranous) parts of the wall: often; seem to be indistinet or 
quite lacking, and as a distinct example hereof I have named 
Sertularia tenera. As I have examined many colonies of. this 
species without finding any other inconstancy in the parts named 
I am sure that the round apertures found by Prof. Nutting, 
must have belonged to regenerated . hydrothecæe and Ritchie”) 
has come to the same: result as I. Of Sertularia robusta I have 
examined a colony from Bering Sea sent to me by the National 
Museum of Washington. All the. hydrothecae present the Ser- 
tularia-characters very distinctly, and when Prof. Nutting in åa 
number of hydrothecae from proximal portions of branches has 
found a different form of aperture and operculum, it is no doubt 
due to cases of regeneration. 
Nutting") declares that the oljkBkbe is almost an ideal 
character to use in separating the "genus Diphasia, but that he 
nevertheless prefers the colonial characters is seen from his refer- 
ence of Sertularia thujarioides Clark- to Thujaria, though it pos- 
1.82 a, p. 22. 
2) 32, p. 189—190. 
5% p. 218. 
sy 44, p. 44. 
