REPORT ON THE HYDROIDA. D9 
parietal fold ; intrathecal ridge obsolete ; mesial nematophore adnate to the hydrothecal 
walls for the entire height of the walls, and then projected as a strong curved spine for 
about the same height ; lateral nematophores wide, conical. 
Gonosome not known. 
Halicornaria plumosa is a singularly beautiful species. Though it is highly probable 
that I have correctly referred it to the genus Halicornaria, this determination cannot, 
in the absence of the gonosome, be regarded as otherwise than provisional. 
One of its most striking features is seen in the very long mesial nematophore, which 
is adnate to the anterior wall of the hydrotheca for its entire height, and is then 
continued as a long, curved, horn-like spine for nearly the same distance. The margin 
of the hydrotheca, instead of presenting the serrated condition usual in the Statoplean 
Plumularidze, is seen, when viewed in profile, to have a deep obliquely-directed notch on 
‘ach side, but is otherwise destitute of serration. The deep fold in the anterior walls of 
the hydrotheca, though occurring in other species, is also characteristic. 
Tn its long mesial nematophore it presents a character in which it would agree with 
Kirchenpauer’s Macrorhynchia section or sub-genus of Aglaophenia. For reasons, how- 
ever, already mentioned,’ the Macrorhynchia of Kirchenpauer can scarcely be accepted as 
a definite group. 
The present species appears to come near to the Hulicornaria speciosa of the Gulf 
Stream exploration.” In general habit there is a close agreement between the two, 
while in both the wide hydrotheea has an anterior parietal fold, and its margin—though 
in the Gulf Stream species this does not present the deep lateral notch of Halicornarva 
plumosa—is in both destitute of true serration, being in Halicornaria speciosa merely 
crenate. The mesial nematophore, however, in Halicornaria speciosa is not continued 
beyond the margin of the hydrotheca in the form of the long, curved, beak-like process 
seen in Halicornaria plumosa. 
That the Gulf Stream species is a true Halicornaria there is no doubt, for the gono- 
some was present in the specimens examined, and removed all difficulty as to generic 
identification. 
Dredged at Station 122, September 10, 1873, off Barra Grande, Brazil, from a depth 
of 32 fathoms. 
Azygoplon, nov. gen. 
Name from afdyos, unpaired, and éhov, a weapon, in allusion to the absence of the lateral 
nematophores. 
Generic Cuaracter. Trophosome.—Hydrocladia pinnately disposed. Mesial nema- 
tophore adnate to the walls of the hydrotheca ; no lateral nematophores. 
1 See above, p. 47. 
2 Hydroids of Gulf Stream, p, 54, pl. xxxiv. 
