782 SOME NEW AND RARE HYDROIDA IN THE AUSTRALIAN MUSEUM, 



In the absence of the gonosome, the present species may be at 

 once distinguished from P. setacea by the calycles being free for 

 part of their length. 



Plumularia alata, n.sp. 



(Plate XIX., figs. 6-10). 



Hydrorhiza with transverse markings along the margin ; 

 hydrocaulus minute, monosiphonic, unbranched, internodes at 

 lower part of stem fusiform, those above more slender, cylindrical ; 

 pinnae alternate, one on each internode of the stem, divided into 

 alternate long and short internodes, of which only the former bear 

 hydrothecae. Hydrothecae tubular, slightly curved outwards, the 

 base springing from a protuberance of the pinna ; aperture partly 

 terminal, emarginate behind, and partly continued as a narrow 

 sinus nearly half way down the front of the hydrotheca ; the sides 

 of the margin forming two lobes, which are somewhat recurved 

 towards the pinna. Intrathecal ridge anterior, projecting from 

 the front extremity of the aperture \ into the cell in a backward 

 and upwai'd direction ; an external narrow projecting web partly 

 crossing the hydrotheca and pinna on each side immediately 

 behind the lateral sarcotheca. Hydrothecal internodes with three 

 transverse folds or constrictions. Sarcothecae bithalamic, canali- 

 culate, slender at the base and moveable ; one immediately below 

 each hydrotheca and two laterals behind it, one between every 

 two hydrothecte, on the intermediate internode, two on each 

 stem-interne de, and a number scattered over the hydrorhiza. 



Gonosome unknown. 



Jfah.- (1) 



This is a noteworthy species for several reasons, not the least 

 of which is its small size. Out of all the specimens examined the 

 largest were only ^ inch in height, or less than any other known 

 Plumularian. The form of the hydrotheca, more especially of the 

 aperture, is unlike that of any other species, the aspect presented 

 in a front view being that of a narrow longitudinal opening half 



