REPORT ON THE HYDROIDA. 
77 
The remarkable network formed by the branches of Dictyocladium dichotomum — 
the only known representative of the genus — confers on this Hydroid a physiognomy, 
one of the most distinct and striking to be found among the Calyptoblastic genera. 
The extent to which the hydrothecse are adnate to the hydrocaulus, and the occurrence 
of joints at distant and irregular intervals, indicate an affinity with Thuiaria, from 
which, however, it differs not only in its reticulate ramification, but in the disposition 
of the hydrothecse on all sides of the branches. 
Dictyocladium dichotomum, n. sp. (PL XXXVI. figs. 2, 2a). 
Trophosome. — Hydrocaulus profusely and dichotomously branched, with the branches 
united so as to form a broad, fan-shaped, angular-mesh ed net, a joint occurring usually at 
the base of one, and sometimes of both arms of the bifurcation, and also here and there 
on the branches at distant and indefinite intervals. Hydrothecse tetrastichous, alternate 
flask-shaped, adnate for more than half their height to the branch, and with the distal 
end continued into a long free tubular neck, which terminates in the small, circular, 
even orifice. 
Gonosome. — Gonangia sessile in the angles of the bifurcations, ellipsoidal, encircled 
by very prominent and regular annular ridges, and having the summit continued into 
a short conical process which carries the small circular orifice on its apex. 
Locality. — Station 162, off East Moncoeur Island, Bass Strait; depth, 38 to 40 fathoms. 
Dictyocladium dichotomum is a very remarkable and beautiful species. The mode 
in which the branches become united with one another so as to form the meshes 
of the net is very singular. When a branch is destined to form a union of this kind 
its distal extremity becomes elongated into a tendril-like continuation destitute of 
hydrothecse. When this meets a neighbouring branch, the end of the tendril unites 
with the branch, not however with any part of the surface of the branch indifferently, 
but, directing itself towards the orifice of a hydrotheca, it here attaches itself, its axis 
becoming directly continuous with that of the hydrotheca. The branches are all in the 
same plane, and the collection contains specimens which have a height and width of more 
than five inches. 
Synthecium, Allman. 
Syntliecium, Allman, Journ. Linn. Soc. Loncl. (Zool.), vol. xii. p. 265. 
Generic Character. Trophosome. — Hydrocaulus divided into definite internodes, 
each internode carrying a pair of opposite hydrothecse, or a single hydrotheca which 
alternates with those of the internodes on each side of it. Hydrothecse adnate for a 
greater or less extent to the internode. 
