270 Mr. R. T. GUntlier on the 



catecl to the ' Gesellscliaft naturforschender Freunde zu 

 Berlin ' the substance of a letter from Dr. R. Bohm, then 

 travelling in Africa, relating to the discovery of a Craspe- 

 dote Medusa in Lake Tanganyika. The information to be 

 gathered from Bohm's account was restricted to the following- 

 points : — that the Medusa was provided with a velum ; that 

 it had a small short broad stomach, at the base of which the 

 genital organs are situated ; and, finally, that the tentacles 

 were very numerous and of unequal lengtli. On account of 

 the complete physical isolation of Lake Tanganyika from all 

 other localities from which Medusas are known, Bohm very 

 justly considered the newly discovered species to be unknown 

 to science, and accordingly proposed the specific name of 

 tanga7}jicce^ leaving tlie generic name, and at the same time 

 deploring that the absence of all necessary literature prevented 

 him from further determining the zoological position of the 

 species. 



Evidently the same animal has since been observed by 

 H. von Wissmann, who, when describing his passage 

 across the lake on the 13th of April, 1887*, says, " I was 

 greatly astonished to observe a number of sea-nettles surround 

 our boat for about half an hour. They were transparent, 

 of the shape of a disk, and like a mark-piece in size ; round 

 the edge was a milky circle, hanging down in fibres, by 

 means of which they swam," 



Such, then, are the sole facts which, so far as I know, have 

 been hitherto published concerning what is probably the most 

 aberrant of the very few freshwater Medusse at present known 

 to us. 



The specimens were preserved in strong alcohol and were 

 much blackened by the osmic acid which had been employed 

 as a fixing agent, and which had acted especially upon the 

 margin of the umbrella and the manubrium. In size the 

 individuals varied from 1 to 1*8 centimetre across the bell, 

 while the largest specimen was as much as 2*2 centim. in 

 diameter. 



The umbrella is characterized by its flattened shape, the 

 diameter being about four times as large as the greatest 

 thickness. The central portion of the umbrella, measuring 

 about two thirds of the whole diameter, is much thickened and 

 has the shape of a nearly hemispherical lens (PI. XIV. fig. 4), 

 while the peripheral portions are very , much thinner. The 

 margin of the umbrella is bent over and incurved towards the 

 mouth. The exumbrella is smooth and covered with an epitlie- 



* H. von Wissmann, ' Throug:!! Equatorial Africa' (English transla- 

 tion), p. 2.53. 



