854 
THE VOYAGE OF H.M.S. CHALLENGER, 
found attached, and, finally, there are true unisexual species, in which small males live 
attached to very large females. 
“ Six genera of sessile Cirripedia have representatives in the collection made during 
the cruise of the Challenger. Acasta and Coronula are represented by one species 
each, Tetraclita and Chthamalus by two each, and one of the species of the latter genus 
has been described as new ; far more interesting, however, are the species of Verruca 
and Balanus brought home by the Challenger. 
“ Verruca was collected at six different Stations, and, though not without hesitation, 
the specimens from each Station have been considered as representing a different species, 
although perhaps it will hereafter be possible to show that two or more of them belong 
to one and the same species. These species 
are especially interesting, because they form 
together a very distinct and characteristic 
division of the genus, showing affinity to 
Verruca nexa as far as regards the perpen- 
dicularity of the walls and the presence of a 
distinct third articular ridge on the outer 
surface of the scutum, a peculiarity which is 
also observed in the fossil Verruca prisca, 
Bosquet. At the same time these new forms 
have shown that the genus has a truly world- 
wide range, and that in the case of Verruca, as in that of Scalpellum, there is coincidence 
of great antiquity with the occurrence at a considerable depth. For, whereas the greatest 
depth from which Darwin got specimens of Verruca was only 90 fathoms, the range in 
depth of the Challenger species is from 500 to 1900 fathoms. 
“ The genus Balanus has twelve representatives among the Challenger species. Of 
these five are new ; three of them, however, are probably nearly related to species des- 
cribed by Darwin ; the remaining two, Balanus corolliformis and Balanus hirsutus, on 
the other hand, representing two closely allied species, scarcely admit of comparison 
with any species Darwin knew. They belong to the deep-sea fauna, one being found 
at a depth of 180 fathoms, the other of even 516 fathoms, and some of the peculiarities 
of their structure must be regarded as standing in near relation to their living at 
so considerable a depth. These peculiarities are the absence of radii and the solidity 
of the parietes ; the former causes the compartments to adhere so feebly as almost 
to separate on being • manipulated. For an animal living near the surface the violent 
beating of the waves would soon prove fatal, if its walls showed the structure of 
the present species. As, moreover, the compartments are solid (not permeated by 
pores), they have by no means the strength of those of other species of the genus. 
“ So we see that though the genus Scalpellum is by far the most remarkable of the 
Fig. 319 . — Verruca sulcata, Hoek. Station 170, off the 
Kermadecs, 520 and 630 fathoms. 
