Australian Hydroids. 341 



Plumulakia filicaulis Poeppig. 



Plumularia filicaidis, Poeppig, Kirch., Abh. Nat. Ver. 

 Hamb., vi., 1876, p. 47, pi. v., fig. 6. Bale, Cat. Aust. 

 Hyd. Zooph., 1884, p. 134, pi. xi., figs. 6, 7, pi. xix.,. 

 figs. 41, 42. Idem, Proc. Hoy. Soc. Vict. (N.S.), vi., 

 1893, p. 115. Idem, ''Endeavour" Report, iii., 1915, 

 pp. 293, 295. Nutting, Amer. Plum., 1900, pp. 60, 76, 

 pi. ii., fig. 6'. Hartlaub, Zool. Jahrb., Suppl. vi., 

 1905, iii., p. 682, fig. M^. Mulder and Trebilcock, 

 Geelong Nat. (2), iv., 1909, p. 34. Idem, Geel. Nat. 

 (2), vi., 1915, p. 52. Idem, Geel. Nat. (2), vi., 1916, 

 p. 80, pi. X., figs. 6a, 6b, pi. xi., figs. 3, 3a. 

 Plumidaria hicerna, Mulder and Trebilcock, Geel. Nat. (2), 

 iv., 1911, p. 122, pi. iii., fig. 4. Idem, Geel. Nat. (2), 

 vi., 1915, p. 52. 

 Antennella filicaulis, Bedot, Rev. Suisse de Zool., xxv., 

 1917, pp. 111-1:24. 

 Experience has shown that it is quite usual in this species for 

 pinnate stems and simple hydrocladia to spring from the same 

 hydrorliiza; the var. indivisa, therefore, which I formerly pro- 

 posed, cannot be maintained. 



In a colony which was growing on Laminaria I found that froms 

 certain points the hydrorliiza radiated in four directions at right 

 angles to each; other. From the central point sprang a pinnate 

 shoot, while the shoots Avhich originated from other parts of the 

 hydrorhiza were usually (but not invariably) simple hydrocladia. 



An interesting feature is the thin and delicate condition of the- 

 lateral sarcothecae, a character which is no doubt correlated with 

 their protected situation partly behind the lateral webs which join 

 the hydrotheca to the hydrocladium. Not only is the sarcotheca- 

 wall thin and towards the base even flaccid, but the septum which 

 in sarcothecae of this type usually divides the cavity into two loculi, 

 is in most cases quite obsolete, so that the sarcotheca is practically 

 monothalamic. But here and there one finds a sarcotheca in which 

 the septum persists in a vestigial condition, l)eing reduced to « 

 very slight annular ridge. 



The delicate nature of the lateral sarcothecae no doubt renderF? 

 them very liable to detachment, and so accounts for the occasional 

 occurrence of specimens in which these appendages are entirely 

 wanting. 



In a paper by Bcdot, just to liand, tlie species is referred to the- 

 genus AnteniH'lla. 



