1910.J FROM CHUI.STMAS ISLAND, 827 



Family iSertulahid.k. 



Sertularella j)oly~oniaa Linn. 

 Thuiaria tiihul'iformis M;trktanner. 



Fuuiily Plumularid.e. 



Plamidaria bttskii Bale. 



Pliimularia setacea Linn. (?) 



I'lnmidarla sp. {^megidocephala Allninn, afl'.). 



J fidicornarla hums Ba.sk, v.*ir. laxa, nov. 



XoTEs OX THE Specimens. 

 GYMNOBLASTEA. 

 Family C l A v i D >E. 

 RiiizoGETON NUDUM Broch (?) 



1909. Rhizogeton muhom Broch, Hydroitlen, in Faun.a Ai'ctica, 

 Jena, vol. v. p. 137, fig. 1. 



On the surface of a fragment of millepore there occurred a 

 delicate stolon from which solitary hydranths sprung at intervals. 

 The stolon is branched, forming a loose, irregular network upon 

 the substratum, and it is protected by a very thin layer of peri- 

 sarc. No perisarc occurs on the hydi-anths, even at the base. 

 The hydranths aie elongated, subcylindrical or spindle-shaped 

 according to the state of contraction. They are armed with 

 long filiform tentacles varying in number from seventeen to 

 twenty-four or twenty-five, and decreasing grad\ially in size, from 

 the longest which, in extension, surround the hypostome, to 

 short, stumpy indivitluals at the base. The tenfaicles are 

 scattei'ed over all but the lower fourth of the hydranth ; but 

 e.xcept for four oral tentacles which lie almost in one whorl, no 

 definite arrangement could be traced. 



The soft parts are well preserved, and in the hydranth a thin 

 ectoderm with flattened cells could be distinguished, lined by 

 endoderm with elongated cells, which project for a short distance 

 into the digestive cavity, and within wliich, in some hydranths, 

 lie clusters of minute, deep-brown, almost opa(pie sphei'ules, 

 probably lefuse products of digestion. The internal portions of 

 the tentacles are filled by a septate skeletal endoderm. The 

 growing point of the stolon, in the one instance observed, was 

 formed of a thick pad of ectodermal cells, which gi-aduall}' dwindled 

 into the insignificfint layer which lines normal portions of the 

 stolon. 



The gonosome was not obsei'ved. 



Dimensions : — 



Stolon, diameter 0*060 mm. 



Hydranth, length 077 



greatest diameter 0'17 



0-92 

 0-21 



to 2 mm. 

 nnn. 



