192 
for specimens collected by the Challenger in the Philippine Archipelago at depths varying 
from 180 to 210 m., has now been found again at a little distance from the former locality, 
namely, 1 degree more to the West and 6 degrees more to the South. Its range of depth 
therefore lies between 180 and 275 m., and it must be considered as an inhabitant of deep 
water. Single or few specimens only were taken on each occasion — it is difficult, however, 
to judge whether it is common or rare from the results of dredgings. 
4. Sectio: Solido-Balanus 
10. Balanus socialis Hoek. Pl. XVIII, fig. 2—12. 
Pe . P. C., Report on the Cirripedia of the Challenger Expedition. 1883, p. 150, pl. XIII, 
—28: 
At several stations, during the cruise of H. M.S. ‘Siboga’’, specimens of a form of 
Balanus were collected, doubtless belonging to the same species, and which certainly show 
the greatest resemblance to the species I described as B. soczalzs in the Challenger report. The 
Challenger-specimens were collected in the Arafura Sea at a depth of about 50 m.; they now 
appear to belong to a form rather common in the Malay Archipelago at depths varying from 
9g to more than 69 m. (PI. XVIII, fig. 2, 10 and-11). - 
I have not much to add to the description of the shell which I gave in my report 
of 1883. There is, however, one important difference that I will at once point out. I said 
with regard to the Challenger specimens, that the walls, as well as the basis, were permeated 
by pores; the numerous specimens I have now investigated, however, have the walls without 
pores, and the basis either indistinctly or not permeated. In smaller species of Balanus it is 
often difficult to arrive at a conclusion regarding this detail of the structure. I made figures 
of two sections of a specimen from Station 164 and I am certain that its walls were not 
permeated. The fig. 4a (Pl. XVIII) shows a section near the orifice, and here the rostrum 
especially presents, near the outer surface, a row of darker spots which could easily be 
confounded with pores “filled up with corium’. The fig. 46 (Pl. XVIII) represents a section 
of the shell of the same specimen near the basis: there is no trace of pores, but the part 
representing the rostrum shows clearly that the wall is strengthened interiorly by vertical 
ribs. I examined specimens from different stations, but I never observed true open pores in 
the walls. With regard to the basis, I saw in a specimen from Station 164 a basis with pores 
or canals radiating from the centre; in another specimen, however, I found lists over the basis 
radiating from the centre and extending to the periphery, and shorter ones alternating with 
the longer ones, and extending from the periphery without reaching the centre. These lists 
look much like canals, and have a darker margin and a clearer longitudinal middle part: they 
are grooves, however, and not canals. 
In most specimens the orifice is rather large, its shape elongately-pentagonal; the shell 
is white, but sometimes, however, dirty-white from mud-particles attached to a thin membrane. 
The radii are narrow, with rounded margins, the alae triangular, with the upper margin parallel 
64 
ee 
ee 
