104 The Genera of the Plumidariidce, 



Besides the Hydroicl Zoophytes which are included in the 

 ''' Catalogue," Dr. von Lendenfeld's work comprises the 

 Tracho-medusee, or Monopsea* of Allman, the graptolites, 

 and the Hydrocorallin^, the last of which are now ranked 

 as a sub-order of Hydroida. (T may mention, however, that 

 several Australian Hydromedusse, which were described, and 

 in some cases figured, by Peron and Lesueur, have been 

 omitted from the list.) Dr. von. Lendenfeld adopts the name 

 Hydromedusse for the whole order, but it seems to me that 

 the term Hydroida is preferable, as some of the members of 

 the order do not, at any period of their existence, develop a 

 medusoid structure. The sub-orders are Hydropolypin^^ or 

 Hydroid Zoophytes whose generative zooids are never of a 

 medusoid nature; the HydromedusinEe, which have gono- 

 phores more or less medusiform in structure; the Tracho- 

 medusinse, which are medusee without a fixed polyp-stage; 

 and the Hydrocorallinse, or calcareous Hydroid corals. The 

 first two of these sub-orders are equivalent to Allman's 

 Eleutheroblastea, Gymnoblastea, Calyptoblastea, and Rhab- 

 dophora. Dr. von Lendenfeld claims that the Hydroida 

 should be classified, like all other organisms, according to 

 the structure of the adult, or the stage of existence at which 

 reproduction is efifected, and likens a system of classification 

 founded on the polyparies to a scheme in which the dried 

 skins of the larvge of Cecidomya should be taken as indi- 

 cating its systematic position, irrespective of the structure 

 of the adult insect. In the construction of genera, however, 

 AUman and Hincks, as well as other recent writers, have 

 given due consideration to the structure both of the repro- 

 ductive zooids and the polype-forms, although their primary 

 divisions may be open to the objection that they are founded 

 partly on larval forms, and may have to be superseded 

 accordingly. Mr. Hincks does not rank the Trachomedus£e 

 even as a sub-order, since he finds that species which have a 

 larval polyp-stage may, as regards the medusa, be absolutely 

 identical in structure with forms in which the medusa is 

 developed direct from the ovum. 



Dr. von Lendenfeld includes in the sub-order Hydromedu- 



* I have inadvertently stated in the " Catalogue" that nothing is known of 

 the Australian members of this group. Not having occupied myself with 

 them, I had overlooked the fact that Peron and Lesueur, Haeckel, and other- 

 writers have described several Australian species of the sub-order, as well as 

 of those families which are supposed to pass through a larval polyp-stage, but 

 whose development has not yet been traced. 



