REPORT ON THE HYDROIDA. 47 
the hydrocladia, are alternate, a very unusual condition in the bipinnate Plumularida, in 
which the primary pinnee are almost always opposite. 
Each primary pinna is supported on’ a short process of the stem, and its proximal end 
is separated from the remainder of the pinna by a very oblique joint, and forms an acute 
wedge-shaped segment, on which the distal portion is, as it were, spliced (see woodcut). 
The joint is occupied by a colourless chitin, and when viewed in profile appears as a broad 
transparent line, which strongly contrasts with the opaque brown periderm of the rest of 
the pinna. The curious splice-like joint thus formed is very striking and characteristic. 
Among the Plumularide described and figured by Kirchenpauer,' are three—Aglao- 
phenia philippine, Aglaophenia urens, and one which he believes he can identify with the 
Plumularia longicornis of Busk. The hydrothecz of all these resemble in many points 
those of the present species, though the habit of the colonies is entirely different. In two 
of them, Aglaophenia philippina and Aglaophenia wrens, he has observed the gonosome. 
Kirchenpauer refers them all to Aglaophenia in the wide sense in which he would 
understand this genus, and places them in a subordinate section or sub-genus of Aglao- 
phenia, to which he gives the name of Macrorhynchia. The group Macrorhynchia, 
however, as defined by Kirchenpauer, can scarcely be accepted, for there may be found 
Statoplean Plumularidee which agree in having the long two-apertured mesial nematophore 
on which the group has been founded, and whose gonosomes are yet so different as to 
render it impossible to associate them in the same genus. Indeed, the form of gonosome 
which Kirchenpauer assigns to his Macrorhynchia may well be referred to the type which 
characterises his Lytocarpia. 
The absence of gonosome in the specimens obtained by the Challenger renders it 
impossible to assign the present species with certainty to a definite genus, but the close 
resemblance of its hydrothecxe to those of the three species just mentioned, in two of 
which the gonosome has been observed, will perhaps justify us in giving it a place in the 
genus Lytocarpus,—a position, however, which, until its gonosome has been examined, 
must have a purely provisional value. 
Mr. Busk’s specimens of his Plumularia longicoriis were obtained during the expedi- 
tion of the “ Rattlesnake,”? and the species defined in the account given of the Hydroids 
brought home by that expedition, From a comparison of authentic specimens in Mr. 
Busk’s possession, with the Lytocarpus longicornis of the present Report, I have 
satisfied myself of the specific identity of the two forms. 
Dredged at Zamboanga, Philippines, January 30, 1875, from a depth of 10 fathoms. 
1 Kirchenpauer, loc. cit., pp. 45-47. 
2 Busk, Voyage of the “ Rattlesnake,” vol. i. p. 399. 
