REPORT ON THE HYDROIDA. 47 



the liydrocladia, are alternate, a very unusual condition in the bipiunate Plumularidce, in 

 which the primary pinnas 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 oblic|Ue 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 Plumularidce described and figured by Kirchenpauer,^ are three — Aglao- 

 phenia pkilippino,, Aglaoplienia urcns, and one which he believes he can identify witli the 

 Plumularia lomjicornis of Busk. The hydrothecae 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, Aglaoplienia philipinna and Aglaoplienia urens, he has observed the gonosome, 



Kirchenpauer refers them all to Aglaoplienia 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 Macrorhijnchia. The group Macrorliynchia, 

 however, as defined by Kirchenpauer, can scarcely be accepted, for there may be found 

 Statoplean Plumularidse 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 Macro rhyncliia 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 hydro thecas 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 Plunndaria longicornis were obtained during the expedi- 

 tion of the " Eattlesiiake," ^ 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 tlic Lytocarpus longicornis of the present Eeport, I have 

 satisfied myself of the specific identity of the two forms. 



Dredged at Zamboanga, Pliilippines, January 30, 1875, from a depth of 10 fathoms, 



' Kircbenpiiuer, loc. cit., pp. 45-47. 



- Busk, Voyagi? of die " Rattlesnake," vol. i. p. 399. 



