with Observations on Australian Hydroids. 97 



genus, which, however, cannot be satisfactorily defined at 

 present, owing to the absence of the gonosome. 



Aglaophenia parvula. Bale. 



The variation of the structure of the corbula in this species 

 is paralleled by that of A.Jiliczda (Allman), a closely-allied, 

 but larger, species. Professor Allman thinks it probable 

 that in A.filicula the closed corbula is the normal form, and 

 that the occurrence of corbula with the leaflets separate is an 

 occasional irregularity. Doubtless the open corbula, which 

 in A. 2^arvula is of comparatively rare occurrence, is a rever- 

 sion to an ancestral type. The closed corbula of this species 

 has a supernumerary rib or leaflet, as in A. filicula, but with 

 'the important diflerence that in the latter species it springs, 

 like the other leaflets, from the rachis, while in A.]oaTVida 

 it is a secondary growth, given ofl" from the first leaflet of 

 the corbula just above the base, and almost at a right angle ; 

 it therefore runs forward about parallel with the rachis of 

 the corbula. It is not present when the corbula is open. 



Aglaophenia divaricata, Bush. 



In A. divaricata, as well as in some other species, the 

 proximal part of the branches is destitute of pinnae for a 

 distance about equal to the length of the pinnae on the 

 main stem, and this portion of the branch bears along the 

 front a central series of sarcothecae, which in A. divaricata 

 are very large. The bare proximal part of the branch is 

 separated from the remainder by a long oblique joint. Small 

 unbranched specimens are generally monosiphonic through- 

 out, the stem not assuming the compound state until the 

 bydrophyton is considerably advanced in growth. 



Aglaophenia longicornis. Bush. 



This species is rather variable in the form of the hydro- 

 theca-margin, which is represented by Professor Allman as 

 only slightly elevated and rounded at the sides, while Mr. 

 Busk describes the hydrotheca as having on each side a 

 broad angular lobe. Sometimes these lobes run up to an 

 acute point. The margin is sub-crenate, but only towards 

 the back, and there is a small tooth where the side joins the 

 lateral sarcotheca, by which it is often concealed when the 

 latter is erect. Between the lateral sarcothecse the back of 



H 



