HYDROID /onl'HYTES. 27 







plan of regarding it as synonymous with " sarcotheca '' and applicable only to 

 perisareal skeleton. Tht> zooid which the nematophore envelopes (in the ca<e of 

 Jfiifi't'iiint only very partially) appears to us to be a true dactylozooid, and we have 

 not adopted the use of any of the terms " sarcostyle," " machopolyp," " sarcodal 

 process, 1 ' etc., suggested by various writers. 



The occurrence of the gonothecrc in " coppinia " masses in our specimens of 

 ] fuJi ciii in iir/mi'i'iiin is a feature of some interest. The number of genera in which this 

 grouping of the sexual zooids occurs is extending as our knowledge advances. 



The gonothecse of the specimens of Halecium m-fioi-emit and If. fi'/i-\ri>j,!,-inn 

 obtained by the 'Challenger' were not observed, but the gouothecre of If. /A.r/A, 

 //. dichotomum, II. fastigeatum, II. Jn'iinii and If. cymiforme obtained by the >ame 

 expedition were not in " coppinia " masses. This peculiar grouping of the gonothecse 

 is not, therefore, a character of the genus, but may indicate a method for the future 

 rearrangement of the species into subgeneric groups. 



HALECIUM ARBOREUM. 

 (Flute IV., figs. 27, 28, 29.) 

 Halefiinn arbmei/m, Alhmin, ' f'li;ilk'iu;vr ' Reports, Vol. XXIII. (.isS.x), \,\. iv., figs. 1-3. 



Localities. The species is evidently abundant in McMurdo Bay, extending from 

 shallow water to depths of 130 fins. 



W.Q., McMurdo Bay, February 20th and 28th, 1902; -20 fms. W.Q., Flagon 

 Point, January 17th and February 23rd, 1903; 10-20 fms. W.Q., No. 6 hole, 

 January 31st, 1903; 130 fms. W.Q., February 21st, 1902; 10 fms. AV.Q., off 

 cable, February 17th, 1904. East End of Barrier, January 29th, 1902; 100 fms. 



The specimens of this species consist of a number of robust colonies rising to a 

 height of 300 mm. from a thick hydrorhizal plexus. A few small colonies from the 

 east end of the Ice Barrier were found attached to the stems of Plumularia. 



Hydrosome. The hydrorhiza is a dense plexus of tubes exhibiting a tendency to 

 be grouped together in polysiphouic bundles. 



The main stem is a thick polysiphonic hydrocaulus 10 mm. in diameter. 



The proximal branches are polysiphonic, like the main stem, and anastomose fivrly 

 whenever they come in contact with one another. The distal branches are much more 

 numerous and usually monosiphonic. The monosiphonic branches (fig. 27) alone bear 

 the hydrothecse, but in some cases these branches still bear hydrothecse after the 

 addition of the first few strengthening tubes. 



o o 



The ramification of the distal branches is pinnate, and in other parts of the colony 

 it is roughly, but not rigidly, nabellate. 



The thickness and roughness of the stem and of the principal branches afford 

 admirable support for the hydrorhizae of other hydroids, a list of which will be found 

 on page 1. 



2 F 2 



