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. lts 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. PI. XVIII, fig. 2 — 12. 



HOEK, P. P. C, Report on the Cirripedia of the Challenger Expedition. 1883, p. 150, pi. XIII, 

 fig. 23—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. socialis 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 

 9 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 1 64 and I am certain that its walls were not 

 permeated. The fig. \a (PI. 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. 4.Ó (PI. XVIII) represents a section 

 of the shell of the same specimen near the basis : there is no tracé 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 ancl a clearer longitudinal middle part: they 

 are grooves, however, ancl 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 



