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The fifth and sixth pairs are nearly equal. They have respectively 25 and 26, and 
26 and 28 segments in the two rami. The anterior face of most segments is furnished with four 
pairs of hairs (PI. XX, fig. 16): one pair (the most distal one) is longer, the second is already 
much shorter, the third is short, the fourth extremely minute. 
Penis long, longer than the cirri. Surface covered with numerous hairs, on the distal 
part especially. Hairs standing off transversely in a peculiar way. No sharp point observed 
dorsally on the basal part of the penis. 
This species was discovered by Dr. G. C. J. Vosmarr in Sponges belonging to the 
species Sfirastrella purpurea (Lmk.) Rdl., dredged at the following Stations: 
Stat. 86. June 18/19, 1899. Anchorage off Dongola, Palos-bay, Celebes. Depth 36 m. Bottom: 
fine grey mud (river mud). 
Stat. 313. February 14/16, 1900. Anchorage East of Dangar Besar, Saleh- (or Sapeh-)bay. 
Depth up to 36 m. Bottom: sand, coral and mud. 
General Remarks. This species occurs in numerous specimens in the sponges it 
inhabits and will also be found, most probably, at other places in the Archipelago. WerLTNER 
(Verzeichniss, 1897, p. 270) mentions B. decivés Darwin as collected by Marrens at Batjan 
(Molucca’s), but I think it possible and even probable that it was not Darwin's species but 
the species here described. I think the difference in shape of rostrum and scutum, and, more- 
over, the narrowness of the carinal-latus, of sufficient importance for not considering the species 
of the West-Indies and that of the East-Indian Archipelago as identical, however nearly related 
they may be. I think that the Siboga-species differs also from Pitspry’s 4. orcuttd which was 
described (Pitspry, Henry A., Notes on some Pacific Cirripedes. Proceed. Acad. of Sci. Phila- 
delphia, 1907, p. 361), on specimens from San Ysidro, Lower California, and which Pirspry 
considers as differing from £. dec/ivis Darwin of the West Indies. The shape of the opercular 
valves, and that of the rostrum of Pirspry’s species, is certainly different from that of the 
same parts in my species. The three species, however, are no doubt nearly related: they may 
be found to be local forms of the same species after all. 
Darwin considered his 2. declivis as belonging to the section E (species with membranous 
basis). I pointed out, under the head of the Genus Zalanus, that I consider this classification 
as more or less artificial. If we take into consideration, not one special character of the forms, 
but their whole structure — the shell as well as the animal itself — we can come to another 
arrangement of the species, and one which, perhaps, gives a better idea of their affinities, so 
far we can judge at present. 
6. Sectio: Armato-Balanus 
16. Balanus terebratus Darwin. Pl. XX, fig. 17—21. Pl. XXI, fig. 1—3. 
DARWIN, CH., Monograph. Balanidae and Verrucidae. 1854, p. 285, pl. 8, fig. 2a—2é. 
Darwin gave a description of this species and proposed a name for it, without being 
able to examine the opercular valves; but, he said, the species here named is so peculiar 
that it would have been a fault to pass it over. There is but a single specimen in the 
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