34 THE VOYAGE OF H.M.S. CHALLENGER. 
huxleyi confer upon this beautiful species an aspect which in gracefulness is perhaps 
not surpassed by any other Plumularian. 
The hydrothecee are remarkable from the way in which the orifice lies in a plane 
parallel to the axis of the supporting internode, instead of being, as in most cases, nearly 
at right angles to it. The internodes are very short, and the hydrothecze are consequently 
brought unusually near to one another. The deep serration of the hydrotheca margin 
usual in the Statoplean section, here gives place to a shallow crenation, and the very long 
curved continuation of the mesial nematophore beyond the orifice contributes still fur- 
ther to the singular aspect of the hydrotheca. In the front of the hydrotheca is a 
strong parietal fold, having some resemblance to an anterior intrathecal ridge, while the 
true intrathecal ridge is nearly obsolete. 
The stem and branches, notwithstanding thei slenderness, are polysiphonic, the 
accessory tubes ceasing a little before the distal termination of the branches, which then 
become monosiphonic for the remainder of their course. 
The gonophore can be seen through the walls of the gonangium to be encircled just 
below its summit by a wreath of refringent spherules, similar to those to which Kirchen- 
pauer first drew attention in the gonophore of his macrorhynchial section of Aglaophenia. 
He believed them to be confined to this group, and incorrectly regarded them as ova.’ 
The phylactocarps are for the most part longer than the hydrocladia, and with the 
symmetrical arrangement of their parts are objects of great beauty, while they are full of 
interest in the evidence they afford of the extent to which various parts of an organism 
may become modified in order to fit them for a change of function.’ 
Mr. Busk has identified the present species with the Pliumularia hucley: of the 
voyage of the “Rattlesnake,” ? and a comparison of the Challenger Hydroid with authentic 
specimens from the collection made during that voyage, has enabled me to confirm this 
determination. 
Dredged at Station 188, September 10, 1874, lat. 9° 59’ S., long. 189° 42’ E.; depth, 
28 fathoms; bottom, mud. Also at Station 190, September 12, 1874, lat. 8° 56’S%., 
long. 136° 5’ E.; depth, 49 fathoms ; bottom temperature 23°°9 C; bottom, mud. 
Aglaophenia, Lamouroux (in part). 
Plumularia, Lamarck, Hist. Nat. des An. sans Vert., 1815. 
Aylaophenia, Lamouroux, Hist. des Pol. Coral. flex., 1816. 
Aglaophenie macgillivrayi, Busk, sp. (Pls. X. and XX. figs. 4-6). 
Plumularia macgillivrayi, Busk, Voyage of the “ Rattlesnake,” vol. 1. p. 400, 1852. 
Trophosome.—Colony attaining a height of upwards of fifteen inches ; stem fascicled, 
1 Kirchenpauer, loc. cit., Band v., Ueber die Hydroidenfamilie Plumularide, p. 16. 
* See general remarks on the morphology of the Phylactocarp, p. 10. 
% Busk, Voyage of the “Rattlesnake,” vol. i. p. 395. 
