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single row of hairs is situated parallel to the inner margin, between the denser tuft of hairs of 
the extremity and the inner lobe. The inner lobe bears numerous long hairs on the semi-circular 
innermost -half; these hairs are distinctly feathered and are directed inwards and downwards. 
The surface of the rest of the inner lobe shows numerous circular pits, looking like so many 
places where hairs might have been disposed (Pl. XIII, fig. 19). 
Cirri. First pair: rarni unequal, but not very strongly; the longer ramus has 17, the 
shorter 13 segments. The shape of the segments may be seen in the figure. The six or seven 
lower segments of the shorter ramus are distinctly protuberant on their inner face, the pigmen- 
tation of the outer half of the segments extending over the protuberances (PI. XIV, fig. 1). 
Second pair has the rami slightly unequal, the longer with 14, the shorter with 
13 segments; the whole cirrus is a little shorter than that of the first pair. The inner faces 
of the segments of the longer ramus more protuberant than those of the shorter ramus. The 
protuberances of the segments of the longer ramus are furnished with very conspicuous and 
dense tufts of hairs (P]. XIV, fig. 2). 
Third pair has the rami also slightly unequal, of 13 and 12 segments respectively. The 
rami are more robust, but hardly longer than those of the first pair. The inner faces of the 
segments of the longer ramus are more protuberant than those of the other ramus. The tufts of 
hairs disposed on the protuberances not so strongly developed as is the case on the second 
cirrus. The projecting membranous plate fringed with fine bristles, which, according to Darwin, 
is found on the thorax, on either side at the bases of third pair of cirri, was found well- 
developed in the specimen investigated (Pl. XIV, fig. 3a). 
Fourth-sixth pairs equal in length and in number of segments. This number was 
found to be 29 — and to vary between 28 and 30. The shape of the segments, in general, 
is quadrate, the middle and lower segments being, however, broader than long, the outer 
segments about as broad as long. The segments (PI. XIV, fig. 4) are slightly shield-shaped 
in front, and bear only two pairs of longer spines: these are wanting on five or six of the 
lower, and also on the last five segments of each ramus. Between the pairs of longer spines a 
group of delicate hairs or spines is regularly observed. The hairs or bristles disposed on the 
posterior side of the segments near the extremity are short. 
Penis. Relatively short, cylindrical, distinctly ringed, tapering towards the extremity. 
Short hairs are scattered over its surface on the distal half, somewhat longer hairs being 
disposed near its extremity. 
As I said already p. 164, the different forms or vagjeties of this species described here 
were taken at the same time from the bottom of the “Siboga’’ when the ship was in the 
dock, October 1899. As is well-known this species is common in all the warmer seas of the world. 
2. Sectio: Ortho-Balanus 
2. Balanus amphitrite, Darwin. Pl. XIV, fig. 8—17. 
DARWIN, CH., Monograph. Balanidae and Verrucidae. 1854, p. 240, pl. 5, fig. 2a—2e. 
This species was collected by H. M.S. ‘“Siboga” at half a dozen Stations and at depths 
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