64 Notices of Memoirs — J. Deivitz — Colour of Lakes. 



being represented in the London Clay by two species of DromiliteSr 

 a very nearly allied form." 



The addition of another new species, apparently related to this 

 family in the Gault, is extremelj^ interesting as exemplifying the 

 close family similarity, but very clear specific and (I venture to 

 think) in this case even generic distinctness from its congeners. 

 It is hoped that before long other examples may be obtained, 

 offering fuller details of its structure ; meantime I publish thi.«y 

 interesting little Crustacean, giving it the name of Mesodromilites to 

 define its older geological position and also its probable relationship 

 to Dromilites of the London Clay, with the specific name of Birleyi, 

 in honour of Miss Caroline Birley, to whom I am indebted for th& 

 opportunity of describing this new Gault crab. 



I. — The Eed Colour of the Salt Lakes in the Wadi Natroun. 

 By J. Dewitz.^ 



IN an article published in the Zoolog. Anzeiger^ I have given 

 a report on the biology of the Natron Valley, the Wadi Natroun, 

 in the Libyan desert, about 170 kilometers from Cairo. It seems 

 that my remarks concerning the red colour of the water of the salt 

 lakes of the valley have interested readers of the article. I there- 

 fore wish to add here some researches I was able to make on the 

 same subject owing to the kindness of Mr. Prochaska, head of the 

 chemical survey of the soda company. 



"When I came to the Natron Valley the red water of the lakes 

 excited at once my curiosity, and I tried to ascertain the reason for 

 the redness of the liquid. Most people to whom I spoke about the 

 matter told me that Artemia lives in the lakes, and that the red 

 colour of this Crustacean is communicated to the water. During 

 my stay in the Wadi the Artemia salina was not to be seen, the 

 animal appearing only at certain periods of the year*. It is im- 

 possible to believe that the coloured mass of these small creatures 

 is sufiicient to stain such immense quantities of water as the Wadi 

 Natroun lakes. These lakes, about fourteen in number, lie rather 

 close to each other and extend over a space of about 40 kilometers. 



No number of Artemia salina would be screat enoug-h to give the 

 water the deep purple colour which it has. If there were frogs in 

 the lakes and those frogs were red, and someone should say that the 

 red colour of the water came from the red colour of the Amphibia, 

 this explanation, I think, would not be much inferior to the Artemia 

 theory. Besides Artemia, there are other red animals in the lakes. 

 I obtained, for example, a red culicid larva. This shows that 

 animals living in the water may take the colour from it, and not the 

 water from the red animals. Finally, Artemia salina disappears in 



1 Eeprinted from Science, s.s., vol. x (1899), Xo. 240, pp. 146, 147. 

 '^ "Das Wadi Natroun iu der libyschen \Yuste und seiae niedern Thiere," 

 Ed. xxii (1899), pp. 53-61. 



