104 Proceedings of the Royal Society of Victoria. 



Idia pristis, Lamx. 

 (Plate IV., figs. 4, 5.) 



In the Challenger Report Professor Allinan has given a more 

 complete account of this remarkable hydroid than had previously 

 been possible, having had the advantage of examining specimens 

 sufficiently well preserved to exhibit much more of the detail 

 than could be made out in ordinary dried specimens. It is 

 through an OAersight, however, that Professor AUman states in 

 two different parts of his work that the species had pi-eviously 

 been known only from Lamouroux' inadequate figure and 

 description and a short notice of the gonosome by Mr. Hincks 

 in the Journal of the Linnean Society of London for 1887, since 

 I had in 1884 described and figured both trophosorae and gono- 

 theca^, while Mr. Busk had described the species in 1852, in the 

 "Voyage of the Rattlesnake" from wliich notice I first identified 

 it. The description of the gonothecte, however, in the work just 

 mentioned was an error, the object described being a parasitic 

 hydroid ( Campaniilaria costatal); but Mr. Busk afterwards 

 observed the true gonothecse and made sketches of then), which I 

 reproduce. The figures of the gonothecte given in the Challenger 

 Report difi*er considerably from the specimens I have seen 

 (which resemble Mr. Busk's figures), especially in showing the 

 longitudinal ribs much closer and terminating at the shoulder 

 instead of continuing up to the margin, while they gi\e no 

 indication of the curved wrinklings of the surface which form 

 series of irregular arches joining all the ribs. Possibly the latter 

 feature is a result of the drying of the perisarc, and therefore not 

 present in well-preserved specimens which have not been dried. 

 The gonothecte are apt to be very irregular in form, sometimes 

 being deeply constricted round the middle, while others have the 

 characteristic ribs absent in parts, and represented by a totally 

 irregular wrinkling of the surface. According to Professor 

 Allman, the hydrothecaj have the peculiarity of opening back- 

 wards by a small valvular operculum, but in specimens which 

 have been dried it is scarcely possible to make out the exact form 

 of the aperture, owing to the collapsibility of the delicate perisarc 

 at that part. The stems of the Challenger specimens appear to 

 be more slender than usual, and the axillary hydrothecje are 



