MIOROHYDRA RYDERI. 623 



On the Medusa of Microhydra ryderi and on 



the Known Forms of Medusae inhabiting 



Fresh Water. 



By 

 Edward Potts, 



Of Philadelphia, U.S.A. 



With Plates 35 and 36. 



The three species of freshwater jellyfish as yet discovered 

 were announced during the years 1880, 1893, and 1897 re- 

 spectively. As the first of these dates was twenty-six years 

 ago, and as the paper reporting the North American form 

 was unaccompanied by illustrative figures, it has been sug- 

 gested to the writer that a general review of the subject, so 

 far as known, would be useful at this time, and the kind 

 assurance was given that if it included " good drawings and a 

 full account of the polyp and medusa" of Microhydra 

 ryderi, it would be gladly accepted and published by the 

 ' Quarterly Journal of Microscopical Science.' 



To make such a re-preseutation of value I propose first to 

 offer copies of the published figures of the earlier forms, viz. : 

 Limnocodium sowerbii, Allman and Lankester; found 

 in the Victoria Regia tanks of Regent's Park Gardens, 

 London, England (PI. 35, figs. 5, 6, 7, 8), and Limnocnida 

 tanganyicse. Dr. R. Bohm, Lake Tanganyika, Central 

 Africa (PL 35, fig. 12). Following these I give figures 

 showing the lateral and polar aspects of the medusa of 

 Microhydra ryderi. Potts (PI. 36, figs. 13 and 14). Both 



