82 THE MEDUSAE. 



development of Polyxenia, in which the gonads form, in addition to the ring, 

 interradial diverticula, as in Pegantha. Polyxenia presents a very puzzling 

 case of nomenclature, since it has been used in different senses by various 

 writers. Eschscholtz, who established the genus for P. cyanostyhs, makes 

 no reference in his notice to a canal system or to marginal sense organs, thus 

 failing to mention the only characters which would help us to locate the 

 species in the family. So far as the gonads are concerned (Eschscholtz, '29, 

 taf. 10, fig. 1), it might equally well belong to Solmoneta. The same is 

 likewise true of the Medusa mollicina of Forskal, since the original figures of 

 Forskal (1776, p. 109; tab. 33, fig. c) resemble in the form of the gonads 

 the well-known Solmoneta flavescens of the Mediterranean. Foveolia diadema 

 Peron et Le Sueur and P. cyanogramma Quoy et Gaimard are based on 

 even less recognizable notices. Therefore there is good room to doubt 

 whether Haeckel's identification of these early names, with specimens which 

 he himself observed, was of much value. Haeckel has described one new 

 species of Polyxenia, P. cyanolina, but very briefly and without figures. 

 Previous to Haeckel's work the name Polyxenia had been used in a very 

 different sense by Forbes ('48), who applied it to P. alderi, a form probably 

 not a craspedote Medusa at all ; and by Metschnikoff ('74), who has described 

 under the name Polyxenia leucostyla Will, specimens probably identical, 

 generically at least, with the long-known Solmoneta flavescens Kolliker. 



In view of the fact that the type species of Polyxenia (P. cyanostyla Esch- 

 scholtz), is unrecognizable generically, and to avoid further confusion, it 

 seems best to abandon the name Polyxenia altogether. If this be 

 done, Polycolpa, which is probably not distinguishable generically from 

 Polyxenia, might well be retained. 



Pegasia lias, it seems to me, a better claim to generic standing, if any 

 specimens normally exhibit the conformation of the gonads described by 

 Haeckel ('79). The only one of the four genera of which a satisfactory 

 account has appeared is Pegantha. 



Vanhdffen (:07), abandoning the conformation of the gonads as a taxo- 

 nomic character in this family, makes the number of tentacles the chief 

 generic character, distinguishing Pegantha with 10-13, Polyxenia with 

 L6-18, and Polycolpa with 25-30 tentacles. The series in the present 

 collection show that this character is so variable that, such slight differences 

 cannot be considered of much importance ; for, according to this scheme, 

 some specimens of Pegantha triloba would belong to Pegantha, others (p. 87), 



