ON VAEIATION IX A JELLYFISH. 1 045 



47. On Variation in the Medusa o£ Moensla lyonsi. By 

 Charles L. Boulenger, M.A., F.Z.S., Lecturer ou 

 Zoology in the University of Birmingham. 



[Received May 23, 1911 : Read June 27, 1911.] 



(Plate LIX.* & Text-figuves 222-228.) 



In 1908 I published an account [1] f of a new lacustrine 

 Hydromerlusan, Moerisia lyonsi, obtained by Dr. Cunnington and 

 myself from the brackish Avaters of Lake Qurun in the Fayum 

 Province of Egypt. 



In my paper, whilst describing the anatomy of this interesting 

 form, I called attention to the fact that the number of tentacles 

 and radial canals in the medusa stage was subject to much 

 variation, and mentioned that in a series of 400 individuals 

 which I examined, 55, or nearly 14 per cent., differed fi-om the 

 normal. 



My descjiption of the abnormal specimens was very short, 

 and it has been suggested to me that it would be of interest to 

 furnish a more detailed account of the variation of this medusa, 

 as well as to figure some of the more peculiar abnormalities. 

 This I was all the more prepared to do, as further study of the 

 collection had revealed additional points of interest in connection 

 with this phenomenon. 



Variation is known to occur frequently in jelly-fishes J, and in 

 some species it has been very carefully studied ; although in many 

 cases the series dealt with were numerically far greater than the 

 one at my disposal, I know of no form in which such a variety of 

 abnormalities occur as in Moerisia. The interest of the series I 

 am about to describe is not diminished by the fact that all its 

 members were collected in one locality a,nd belong to the same 

 sex. 



As the greater part of my material had already been distributed 

 when I decided to take up this subject again, it was necessary to 

 re-examine the specimens in the Natural History Museum, 

 London, and in the Cambridge Museum of Zoology ; for permis- 

 sion to do this, I have to thank Mr. R. Kirkpatrick and Mr. L. 

 Doncaster, under whose charge the specimens are preserved in 

 these institutions. 



In my description of Moerisia lyonsi, I drew up the following 

 table to show the number and arrangement of the radial canals 



* For explanation of the Plate see p. 1056. 



f The figures in brackets refer to the List of References on p. 1055. 



J Cf. List of References on p. 1055. 



Peoc. Zool. Soc— 1911, 1^0. LXXT. 71 



