299 
abcauline, In such a manner the opercular appåratus of ;$. Rath- 
buni has been interpreted by Nutting!) and Ritchie?), and 
that of 5. heterodonta by: the latter author ?), but the supposed two 
distal valves are really only the two halves of the angularly: bent 
adcauline membrane. ; 
I have already pointed out that Nutting regards the oper- 
cular apparatus in Sertularia as ”shaped like the side walls of an 
"AV tent, the front and rear of the tent being closed by the two 
opposite hydrothecal teeth”, and as a typical example he describes 
the development and structure of the operculum in $. pumila. At 
the same time, however, Nutting's figures of S. cornicina, S. 
Mayeri, S. brevicyathus and S. flowersi distinctly show that the 
operculum in these species cannot be constructed in the above 
manner, the aperture being provided with an adcauline median 
projection and an angularly bent adcauline wall In such of the 
author's figures which present the hydrothecae regarded from the 
side, as f. inst. those of S. Pourtalesi!) and S. exiguaY), only 
the one lateral half of the. angularly bent adcauline membrane is 
seen. I have seen, however, å few species, in Which the operculum 
is construeted in the manner described ”by Nutting, and that is 
the case in S. Suensoni n. sp. (pl.'IV,: figs. 16—20), S.' grisea 
Krp. (= $. similis Clark), and in that form which'Marktanner- 
Turneretscher%) has described under the name S. difusa Allm., 
var. To judge from the figure given by the author Sertularia 
(Sertularella) Clarki Mer. seems to have a similar operculum. In 
these species the adcauline sinus has no median projection, the 
adeauline membrane is not angularly bent, and both: opercular 
membranes, which have an almost straight free edge, form with 
each other. an acute angle. An adcauline median prøjection and 
an angular bending of the adcauline wall we also lack in SS. 
Nuttingi mn. sp. (pl. IV, figs. 1—4) in which the bottom - of the 
sinus is convex aud the adcauline membrane very short. The same 
1) 44. | 
3) 51; 
Sy 36, 
