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Sertularella (Grav.) Nutting. 
Among the species which Nutting selects as examples showing 
inconstancy in the hydrothecal characters aie the following thiee 
species, which he refers to the genus Sertularella. For each of 
them we shall quote that part of the author’s description which 
refers to the hydrothecal margin and the operculum: 
S. formosa Fewkes. “Aperture perfectly round and smooth. 
Operculum apparently wanting. Sometimes, however, it appears in 
the shape of a thin membrane stretched like a drumhead across 
the aperture.” 
S. Hartlaubi Nutting. “Margin perfectly smooth and even; 
operculum in some cases an adcauline flap; in others apparently 
an irregularly ruptured membrane, stretched across the aperture 
like a drumhead.” 
S. magna Nutting. “Operculum thick conspicuous, a simple 
membrane of a simple flap where the margin is even, with two 
flaps when there are two evident teetb, sometimes apparently with 
more than two flaps, but they are not well defined, piobabl) 
because the teeth when three or four, are very low and incon- 
spicuous. No better example could be found of the futility of basing 
generic distinction on the number of parts to the operculum. One 
branch could be placed in three different genera, were that criterion 
to be used. 1 ’ 
I have not seen the two first named species, but the de- 
scriptions and the figures leave no doubt that they cannot be 
referred to Sertularella. There is not the faintest indication of 
marginal teeth, and the thin membrane stretched like a diumhead 
across the aperture is no doubt the original membranous roof of 
the hydrotheca, which is found in all Thecaphora. The author 
does not mention whether he has found this membrane also in 
old hydrothecae. It is possible that a number of Sertularella - 
species may have developed from that group, to which they belong, 
by a transformation of the membranous roof into a Sertularella- 
operculum, but as they themselves lack the chief-characteis of 
