213 
Penis much longer in the one than in the other specimen. In both it tapers very 
considerably towards the extremity and it is furnished with only very few hairs. No point observed 
on the dorsal side near the basis. 
This species was collected at Banda at a depth of g—36 m. The specimens are numerous, 
and are attached to pieces of stone, probably of Madreporian origin. To one of these stones 
a piece of a rather thick membranous coat, containing numerous polyps, is still attached; the 
Balant, however, are found only on the surface of the calcareous mass, where this membrane 
is wanting. Some specimens show the structure of the shell, its colours, etc., as described, but 
others have the surface uniformly white, or look as if their surface was corroded and then 
resemble more or less the stoney matter to which they are attached. To one of these pieces 
of stone a specimen of 4. amphitrite was also found attached, and another specimen of the 
latter species almost completely overgrows one of the specimens of B. arcuatus. 
General Remarks. I think that this species is in general related to several species 
of my group. Yet it has in other respects — in the narrowness of the carino-lateral compart- 
ments, in the shape of the tergum, in the structure of the radii, etc., — much that is peculiar 
to it. It comes near to B. a/dzwm Darwin: I have been long doubting, whether it did not belong 
to that species. I finished with considering it as distinct, not so much because the basis of my 
species is perfectly flat — the basis of 4. aldium according to Darwin is concave, can be 
more or less cup-formed, and is more or less deeply imbedded in the coral — but for the very 
peculiar shape of the tergum in the Banda specimens. The very striking impression which the 
orifice with the white beaks of the terga makes would certainly have been noticed by Darwiy, 
and in his description of 4. al/ium he merely says, “Tergum with the apex somewhat produced 
or beaked”. What Darwin reports on the structure of the mouth and the cirri corresponds 
fairly well to what is seen in my new species — there are differences, however, which make it 
more probable that the two forms are nearly related, than that they will prove to be identical. 
18. Balanus guadrivittatus Darwin. Pl. XXI, fig. 15—20. Pl. XXII, fig. 1—2. 
DARWIN, CH., Monograph. Balanidae, Verrucidae etc. 1854, p. 284, pl. VIII, fig. 1. 
At Station 164, attached to stones, together with specimens of &. soczalis, small 
specimens of a Balanus were collected, which turned out to belong to the above-named species. 
In general the Siboga-specimens agree with Darwr’s description of this species. The 
shell is conical (Pl. XXI, fig. 15), somewhat depressed, with a small irregularly rhomboidal or 
sometimes pentagonal orifice. The surface of the shell shows longitudinal folds extending from the 
orifice to the margin of the base. The radii are narrow and have oblique summits. Colour dirty 
white, surface covered, however, with a layer of yellowish mud. Some of the specimens — 
not all — show, on rostrum, carina and latera, the four brownish-grey bands, which suggested to 
Darwin the present name of the species. I saw other specimens without a trace of these bands. 
The basis is very thin, calcareous, brittle — I could not discover pores, either in the basis, 
or in the compartments or radii. The basal diameter of one of the larger specimens was 
at the most 3 mm. 
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