Invalidity of the Hydroid Genus, Diplopteron, Allman. 7 
be considered as appendages supplementary to the primary lateral sarcothece. 
Such supplementary lateral sarcothece are exhibited by the species re- 
described in the preceding paper—Plumularia catharina, Johns.,—by 
Antennopsis scotwv, Ritchie,’ Diplopteron insigne, Allman, Antenella quad- 
riurita, Ritchie, and A. siboge, A. varians, and A. balei, all of Billard; 
although the three last possess in addition paired sarcothece of the 
indefinite type. 
Anterior aspect of Polyplumularta flabellata,? 
showing indefinite type of arrangement of 
additional pair of lateral sarcothece. x 88. 
(Compare Plamularia catharina, with defin- 
ite arrangement, Fig. 3 of preceding paper, 
p. 3.) 
The presence, therefore, of more than one pair of lateral sarcothecz occurs, 
according to present classification, in, at least, these genera of Plumularidae— 
Plumularia, Antenella, Diplopteron, Polyplumularia, and Antennopsis. These 
genera are distinguished by characters of branching, of arrangement of 
hydrocladia, and by the presence or absence of special offshoots of the 
hydrocladia for the protection of the gonangia. However one may regard 
the exclusive use of characters of branching in distinguishing genera, it is 
impossible that all the distinguishing features involved in the separation of 
these genera are to be nullified in view of the presence of additional pairs 
of sarcothecz, which, as has been indicated, belong to two distinct types. 
The genus Diplopteron, which was formed to contain such diverse forms 
as have been enumerated, seems to me therefore to be untenable. 
1 See Ritchie, Trans. Roy. Soc., Edinburgh, 1909, vol. xlvii., pt. i., p. 90, fig. 8. 
* Specimen from Loch Lorne, Scotland. 
Issued separately, 23rd January 1913.)} 
