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The specimens collected by H. M. S. “Siboga’”’ are from three different Stations, and 
have a greenish-grey colour in the preserved condition. The outer lamina are only partly 
removed in the younger specimens, much more so in the larger specimens. The size and 
shape of the shells is rather different, radii are distinct in some specimens and hardly disting- 
uishable in others; some have very small orifices, others much larger ones. But the shape aad 
structure of the opercular valves is the same or nearly the same in the different specimens ; 
they closely resemble the figures and correspond to the description given by Darwiy. 
The most typical specimens among those of H. M. S. “Siboga’” were collected at 
Station 152 during reef-exploration. According to the list, the depth at that Station was 32 m. 
and the bottom was covered with Lzthothamnium. The shape of these specimens is conical, 
their colour greenish-grey, the exposed parietal tubes dark, nearly black. The orifice is irre- 
gularly rounded and large, the sutures of the compartments are not quite distinct, much more 
distinct, however, in one of the specimens, than in the others. A narrow but distinct radius 
is represented almost at every suture in this specimen. The diameter of the largest specimen 
was 38.5 mm. at the basis; the thickness of the wall was here about 8 mm. The opercular 
valves of one of these specimens were carefully cleaned, and found in perfect agreement with 
Darwiy's description, not considering little differences in colour, and in the degree in which the basi- 
tergal angle of the scutum is rounded off, etc. In this specimen, the adductor ridge of the scutum 
extends quite to the apex of the valve, as Darwin says it does in some specimens. Its 
tergum has a distinct beak, the spur is quite close to the basi-scutal angle and its extremity 
is pointed, perhaps not quite so sharply as Darwin says it is in one of the varieties, but 
sharper certainly than in the two forms figured by Darwin. 
This form comes nearest to 7. forosa var. (3) verzdis of Darwin; the inner surface 
of the opercular valves, however, is not “clouded green” as Darwin said, but rather bluish- 
black. These specimens were collected during reef-exploration at Wunch-bay, N.W.coast of 
Waigeu-island [Station 152, August 12/13, 1899.] (Note. A sample of specimens collected during 
the New-Guinea-Expedition of 1903 (February 13") in the Bay of Mawi corresponds in most 
respects to those of Station 152.) 
In the second place, there are specimens from Station 131. They are much smaller 
than those from Waigeu-island and form two clusters of 7 to 9 specimens each. Their shape 
is not conical, but some are depressed, others rather globular with relatively small orifices. 
The surface is irregularly ribbed, the ribs more or less distinctly serrated near the base. The 
outer lamina of the shell is quite preserved in some specimens, in most removed near the 
orifice; the colour of the specimens (in preserved condition) is greyish-green and the parietal 
tubes are blackish where exposed. Radii and sutures very indistinct. Size: largest diameter of 
the basis 12 to 16 mm., height 7 to 9 mm. The opercular valves are much like those of the 
specimens from Station 152, the scutum having the adductor ridge extending to the apex 
of the valve, and the tergum being beaked and having the spur quite close to the basi-scutal 
angle. The extremity of the spur, however, is more bluntly pointed. 
This form resembles 7. serrata Darwin, to a certain extent; on the other hand it is 
so much like a true -7. forosa that it seems impossible to separate it from that species. 
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