330 SIR SIDNEY F. IIAKMER ON 
present, in the form ol: avicularia, occasionally vibraculoid, or of vibracula. 
Rootlets given off by the basal heterozooecia or from the sides of the marginal 
zocecia, passing prosimally as marginal bundles down the colony and 
frequently extending round the axils of the bifurcations. Ovicells typically 
small, often with a frontal fenestra. 
Distribution, circumpolar (Southern), reaching as far north as Victoria 
in shallow water and Valparaiso in deep water. 
The characteristic features of this genus appear to be the pluriserial 
branches, which are usually more or less semi-cylindrical, with the zocecia 
opening on the curved surface ; the tendency for the basal walls of some of 
the inner zocecia to be reduced ; the occurrence of basal heterozocecia (some- 
times wanting) ; and the arrangement of the rootlets in marginal bundles. 
The last character also occurs in Aienipea and Notoplites. The genus is of 
special interest as demonstrating, better than any other, the intimate relation 
between avicularia and vibracula. Joints definitely associated with a bifur- 
cation seldom occur, but there is reason to believe that even in " unjointed '' 
species they may be formed secondarilj', as fractures occurring at some point 
of an internode, the fracture being menijed by the formation of chitinous 
connecting tubes formed externally to the zocecia and not as a modification of 
their own body-walls. It is not unlikely that I have included too many 
species in this genus, which may have to be further subdivided. 
1. Amastigia nuda. Busk. (PI. 17. figs. 21, 24, 25 ; PI. 19. figs. 50, 51.) 
Amastiyia 7iuda, Busk, 1852°, p. 40, pi. 36. figs. 1-5. Tierra del Fuego. 
„ „ (pars), MacGillivray, 1887, Trans. Proc. R. Soc. Vict, xxiii. p. 200. 
Victoria. 
The interest of this remarkable species seems to have completely escaped 
recognition since the publication of Busk's original account. MacGillivray 
records it, on the authority of J. Bracebridge Wilson, from Victoria, and the 
record is confirmed by slides in the British Museum. Kluge (1914, p. 613) 
mentions the genus only to dismiss it. 
The type-slide (Brit. Mus. 54.11.15.87), from material collected by Charles 
Darwin, shows some interesting peculiarities which were not noticed by Busk. 
The branches are at first biserial, and the zocecia of the two rows hei'e meet 
one another, in a normal manner, in the middle line of the basal surface. 
They later become 3-serial, and then 5-serial, by the intercalation of three 
additional rows. A basal view of a 5-serial region shows the appearance 
indicated in PI. 17. fig. 24. The greater part of the basal surface is formed 
by the marginal zocecia (1, 5), while the median (3) and submedian (2, 4) 
zocecia have only a restricted origin from this wall. The frontal surface is 
very convex, the middle region being much thicker than the sides, and the 
marginal zocecia face obliquely outwards. As shown in Busk's figs. 2, 3, 
there is a large, undivided scutum, rounded distally. A frontal avicularium 
may occur on the submedian zocecia, but there is usually a pair on those of 
