74 MR JAMES RITCHIE: SUPPLEMENTARY REPORT ON 



On the branched specimen two branches, which appear to belong to the colony, since 

 they lie in the same plane and leave the stem at the same angle as the true branches, 

 were found, on microscopic examination, to be specimens of Halicomaria longicauda, 

 arising from hydrorhizal tubes climbing upon the stem of the Aglaophenia colony. 



Locality. Station 81, Abrohlos Bank, Brazil. Lat. 18 14' S., long. 37 58' W. 

 Depth, 36 fathoms. Bottom deposit, coral. 20th December 1902. 



Aglaophenia heterodonta, Jaderholm, 1903. 



Dr ELOF JADERHOLM has described amongst the extra-European Hydroids in the 

 Swedish Museum specimens of A. dichotoma (M. Sars), as distinct from a form with 

 similar habit which he has named A. heterodonta. I now regard the specimens which 

 were described in the earlier Scotia report under the name of A. dichotoma as examples 

 of A. heterodonta. 



Additional material enables me to add to JADERHOLM'S description of the general 

 habit of the colonies. His specimens were characterised by irregularly ramified stems 

 bearing short, upward curling twigs. Our specimens exhibit two types. The first, pre- 

 viously described (RITCHIE, 1907, (I) pi. iii. fig. 2), is strictly dichotomous, although the 

 branches may not develop equally in all parts of the colony. This type of branching 

 is exactly similar to that of A. dichotoma. The dichotomously branched specimens 

 were growing on a sponge, and are considerably taller (10 cm.) than JADERHOLM'S 

 examples (3'5 cm.). The habit of the second type is distinctly reminiscent of that of 

 A. conferta, Kirchenpauer, 1872; that is to say, simple curved stems spring in pro- 

 fusion from a hydrorhiza creeping upon an alga. There is no sign of branching. The 

 largest of those colonies is only 18 mm. high, but that they are fully developed is 

 shown by their sexual maturity, for several bear corbulse with male gonophores. The 

 minute characters of the two types of colonies are identical, and agree with those of 

 A. heterodonta. It may be, however, that this is but a synonym of A. conferta, 

 the only characters which seem to separate the latter being the absence of an 

 unpaired anterior reflexed tooth (which, however, appears to be present in KIRCHEN- 

 PAUER'S figure) ; the outward, instead of the inward, direction assumed by the pair 

 of teeth nearest the stem ; and the angled nature attributed to the supracalycine 

 nematophores. However, it is only by examination of KIRCHENPAUER'S type that 

 such a question could be decided. 



That the branched and unbranched colonies are found on two different types of 

 substratum probably indicates that they are environmental modifications ; the fixed, 

 settled colony (that on the sponge) becoming luxuriant, while the drifting, unsettled 

 colony (that growing on the alga) tends, as do so many alga-borne Hydroids, to remain 

 dwarfed and of simple habit. 



The development of the corbula differs slightly from that of A. pluma as described 

 by ALLMAN (1871, p. 59) and NUTTING (1900, p. 40), for the leaves develop less simul- 



(ROY. soc. EDIN. TRANS., VOL. XLVII., 96.) 



