84 The Genera of the Plumulariidoe, 



" Catalogue" that such species should rather be associated 

 with those in which the gonangial pinnse are still further 

 altered, and that only the species with unprotected gonosomes 

 should be included under Halicornaria. Professor Allman 

 independently came to the same conclusion, and^ in the 

 " Challenger" Report, proposed the genus Lytocarpus (an 

 adaptation of Kirchenpauer's sub-genus Lytocarpia) for the 

 species which have the gonangia borne on modified pinnae; 

 but also included in it a section of the corbula-bearing species. 

 This appears to me by no means the most natural arrange- 

 ment, as will be apparent if we divide the species of 

 Aglaophenia and Lytocarpus admitted by Professor Allman 

 into three groups, as follows: — 



1. A corbula present, the ribs of which form leaflets, and 

 do not bear hydro thecse (Aglaophenia, Allman). 



2. A corbula present, the ribs of which bear a single 

 hydrotheca near the base, and do not form leaflets {Lytocarpus, 

 Allman, part). 



3. No corbula, gonangia borne on scattered modified pinnse 

 (Lytocarpus, Allman, part). 



In view of the fact that the first and second of these 

 sections agree in the presence of a corbula — which, moreover, 

 is in each case formed from the same structural elements, 

 only somewhat differently modified — while in the third group 

 the corbula is entirely absent, it seems evident that the first 

 two groups are much more nearly allied to each other than 

 either of them is to the third, and, consequently, if there is to 

 be any generic separation, this group must stand alone. I 

 propose, therefore, to modify the generic description of 

 Lytocarpus so as to make it include this section only — that 

 is to say, all the species in which the gonangia are borne on 

 pinnaB, the distal portions of which are modified by the 

 suppression of the hydrothecse, so as to form nematocladia. 

 It is to be observed that it is not the scattered position of 

 these nematocladia which so sharply distinguishes this section 

 from all the true corbula-bearing species (in fact, the 

 Lytocarpus raceriiiferus of Allman has the nematocladia 

 brought together in a special part of the branch, so as to form 

 what may be called a " pseudo-corbula") ; but the fact that 

 the true corbula is composed of nematocladia which are not 

 modified pinnae, but secondary structures springing from the 

 pinna3, and not represented at all in the species which I would 

 assign to Lytocarpus. 



