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 9 — 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 

 Balaui, 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 B. amphitrite was also found attached, and another specimen of the 

 latter species almost completely overgrows one of the specimens of B. arcuatus. 



General Rem ark s. I think that this species is in general related to several species 

 of my group. Vet 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. allium 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 B. allium 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 certainiy have been noticed by Darwin, 

 and in his description of B. allium 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. Balauus quadrivittatus Darwin. PI. XXI, fig. 15 — 20. PI. XXII, fig. 1 — 2. 

 Darwin, Ch., Monograph. Balanidae, Verrucidae etc. 1854, p. 284, pi. VIII, fig. 1. 



At Station 164, attached to stones, together with specimens of B. socialis, small 

 specimens of a Balauus were collected, which turned out to belong to the above-named species. 



In general the Siboga-specimens agree with Darwin's description of this species. The 

 shell is conical (PI. 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 tracé 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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