HYDROID ZOOPHYTES COLLECTED BY DR WILLEY IN THE SOUTHERN SEAS. 457 



are formed of the mesial sarcothecae of a hydrocladium or ultimate pinna, wliich, deprivi^d 

 of their hydrothecae and lateral sarcothecae, are thrown off to left and right alternately 

 up the pinna, giving off secondary sarcothecae which continue the ribs upwards. The 

 position of the corbula taking the place of a hydrotheca bearing pinna and the 

 number of the costae corresponding with the number of hydrothecae on these pinnae, 

 allowing for the one complete hydrotheca which is always present below the corbula 

 in these specimens, makes it seem natural that the corbulae are formed thus. 



There are only a few species known of Aglavphenia which have the doubly 

 pinnate ramification and the bithalamic form of mesial .sarcotheca, and A. Macr/illivrai/i 

 is the only representative in Australian seas. 



Locality. Engineer group, British New Guinea. 



Gexus. Pluinularia, Lamarck (in part). 



Plumidaria compactu, n. sp., PI. XLIV. Fig. 3. 



A good large quantity of this species was found. The colonies resemble the 

 description by Mr Bale' of a small variety of Plumularia setaceoides, Bale-. They 

 are pale horn colour, unbranched, 1'.5 cm. in height. The pinnae are alternate and 

 bear four hydrothecae at most, which have even rims and a mesial and two lateral 

 sarcothecae, while there is also a sarcotheca on an internode between every two hydm- 

 theca-bearing internodes and one on the lower part of each stem internode. 



The gonothecae grow near the bases of the .stems, below the pinna-bearing 

 internodes. They differ from those of P. setitceoides, which are obliquely truncated a 

 little above the broadest part, in tapering upwards from the broadest part about as 

 much as they taper downwards below it and in terminating with a neat rim. These 

 gonothecae show clearly that this is not Mr Bale's P. setaceoides: it may be what 

 he described as a smaller variety, in which he found no gonothecae, but in that case 

 it must become the independent species — which I have described above as P. comjxicta. 



Locality. New Caledonia. 



' Catalogue of the Australian Hydroids, 1SS4. 

 ^ JouTH. Mic. Soc. Vict., 11. (fig.). 



