with Observations on Australian Hydroids. 85 



Coming now to the question as to whether the first two 

 of the foregoing groups should be re-united under 

 Aglaopheniaj or whether the second should be considered a 

 distinct genus, I am strongly inclined to adopt the former 

 course. The distinctions between these two groups, as laid 

 down by Professor Allman, are simply that in the first the 

 corbula-ribs form leaflets, and do not bear hydrothecse, while 

 in the second they are rod-shaped or sabre-shaped, and have 

 a hydrotheca near the base of each. If these differences 

 were constant they might be deemed of generic importance ; 

 but in such species as A. divarica-ta (Busk) and A. acantho- 

 €aTpa {Allmsiii) the ribs are almost filiform, and certainly do 

 not merit the name of leaflets so much as do those of 

 A. distans (Allman), which, nevertheless. Professor Allman 

 would now place under Lytocarpus, presumably on 

 account of the ribs bearing hydro thecae ; while in A. vitiana 

 (Kirchenpauer) we have a species in which the ribs of the 

 corbula assume the form of broad leaflets, like those of 

 A.pluma and its allies, except that they are only united to 

 each other at intervals along the margins instead of con- 

 tinuously, and yet bearing each a hydrotheca, as in the species 

 of the other section. Seeing, therefore, the impossibility of 

 ■drawing any satisfactory line between them, I regard all the 

 true corbula-bearing species as belonging to the genus 

 Aglaophenia, the essential character of which will be the 

 possession of a corbula, the ribs of which are secondary 

 structures, springing from a modified pinna, and consisting of 

 the modified mesial nematophores of the hydrothecae near 

 their base, which hydrothec£e may be either present or 

 suppressed. 



The Lytocarpus secundus of Allman is a very exceptional 

 species, but if, as Professor Allman supposes, the single 

 series of nematocladia borne by the gonangial pinna be 

 homologous with the ribs of the eorbula of Aglaophenia, it 

 may be regarded as an aberrant form of that genus. This 

 seems the more likely, from the fact that the spine-like 

 nematocladia are only borne on alternate internodes, as if 

 the whole of one series had been suppressed. 



The homology of Aglaophenia myriophyllum seems to be 

 in dispute, as Professor AlJman says that its corbula consists 

 of ribs formed exactly as in other species by the modification 

 of the mesial nematophores of the hydrothecEe at their base ; 

 while Mr. Hincks states that these structures "do not take 

 the place of the anterior sarcotheca, which is present, as 



