REPORT ON THE HYDROIDA. 35 
sending off closely-set opposite primary pinne, which are destitute of hydrothecs, but 
carry from end to end the proper hydrotheca-bearing pinnee, which are about one-tenth of 
an inch in length, alternately disposed, and borne also by the main stem in the intervals of 
the primary pinne. Hydrothecw closely approximated, rather deep, with a well-marked 
intrathecal ridge, margin entire, sigmoidally curved ; mesial nematophore adnate by its 
whole length to the hydrotheea, with its sides parallel in profile, diverging from below 
upwards in front view, its distal end terminating close to the margin of the hydrotheca 
by a wide orifice, a short distance behind which is a transverse septum-like fold ; lateral 
nematophores wide, overtopping the hydrotheca ; hydrothecal internode with strong 
obliquely-directed intra-cauline ridges. 
Gonosome.—Costze of phylactocarp intimately fused together, so as to form a long 
nearly cylindrical, completely closed corbula, whose sides support seven or eight trans- 
verse series of slightly elevated ramified ridges, with every branch supporting a wide 
cup-shaped nematophore, and with a strong spur-like nematophore at the hase of each 
series. 
Aglaophenia macgillivray’ presents many features in which it differs from the typical 
Aglaophenie. Its doubly pinnate ramification affords in itself a character which contrasts 
markedly with the ramification of nearly all the other known species. This character 
shows itself in the thick, strongly-fascicled stem being closely set with opposite pinne, 
which are themselves destitute of hydrothece, but give support to the proper hydrocladia, 
which are disposed in alternate pinne from end to end of the opposite or primary pinne. 
Here and there the primary pinnz become developed into long branches, which then re- 
peat in all respects the ramification of the stem. The absence of true serration in the 
margin of the hydrotheca, and the bithalamic condition conferred on the mesial nemato- 
phore by the presence of an imperfect septum, are other important points in which Aglao- 
phenia macgillivray: differs from the typical Aglaophenie ; while in the corbula, with its 
parietal ramifying ridges, we find a still further distinctive feature. 
A comparison of the Plumularidan here described with authentic specimens of Plumu- 
larvia macgillivrayi, Busk, brought home by the “ Rattlesnake,”" establishes the identity of 
the “Rattlesnake” species with that of the Challenger. Kirchenpauer places it in his 
special section or sub-genus of Aglaophenia, to which he gives the name of Pachy- 
rhynchia, and which he bases on the supposed excessive width of the mesial nemato- 
phore, believing the nematophore to surpass in this respect the hydrotheca to which 
it belongs.? I am unable, however, to accept this character as a ground for the establish- 
ment of a distinct group, more especially as its reality is not borne out by an examination 
of well-preserved specimens, and Kirchenpauer’s figures seem to have been made from 
specimens whose had state of preservation rendered them deceptive. The mesial 
1 Voyage of H.M.S. “ Rattlesnake,” vol. 1. p. 400. 
2 Kirchenpauer, loc. cit., p. 20, 
