32 HALOPTERIS. 
Plumularia geminata. 
Pi. XX. Figs. 1-4. 
Trophosome. — Stem attaining a height of about one inch, dichotomously 
branched ; internodes towards the distal extremity of the branch alternately 
longer and shorter; each shorter internode carrying near its middle a 
hydrotheca, on each side of which springs an ultimate ramulus, also com- 
posed of alternately longer and shorter internodes; each shorter one 
carrying a hydrotheca. Hydrothecze campanulate with slightly everted 
margin, free for about its distal half. Lateral nematophores borne each 
on a strong tooth-like process of the internode; mesial nematophores 
carried upon both the hydrothecal and the intervening internodes. 
Gonosome. —Gonangia pyriform, borne on short two-jointed peduncles 
which spring from the mesial line immediately below the hydrotheca, the 
narrow proximal end of the gonangia carrying a nematophore on each 
side. 
Off Sand Key, from a depth of 120 fathoms. 
Plumularia geminata is a very remarkable form; the ultimate ramuli given 
off in regular pairs from the principal branches confer upon it a very 
striking aspect. All these pairs of ramuli are directed towards one side 
of the branch from which they spring. The proximal joint of each hydro- 
theca-bearing internode in the ultimate ramuli is very oblique, the distal 
one transverse. This internode carries a single mesial nematophore, which 
is situated at the proximal side of the hydrotheca, while each intervening 
internode of the ramulus carries three. In the main branches each hydro- 
theca-bearing internode carries also a nematophore at the distal side of 
the hydrotheca, while four nematophores are borne on every intervening 
internode.* 
HALOPTERIS ALLMAN nov. gen. 
Generic CHaracter. Tyrophosome.— Hydrosoma pinnate plumose; stem 
and pinne divided into internodes. Hydrothec adnate to side of pinne, 
unilateral. A pair of nematophores flanking the hydrotheca, one on 
each side, and adnate to it. Mesial nematophores two (or more), not 
adnate to the hydrotheca, fixed, monothalamic, with an oblique aperture 
continued into a lateral slit. 
Gonosome not known. 
* See Addenda, p. 56. 
