ALG^. l8l 



upper region of the atmosphere, or these two species 

 are yet to be discovered elsewhere. 

 ' Other Atlantic showers were examined from col- 

 lections made by Darwin between the years 1834 and 

 1838, part at San Jago, Cape de Verde, and part 

 within two hundred and fifty miles of the land in the 

 open sea. They afford thirty new forms to those of 

 the above shower, and include also the same South 

 American forms. In addition there are three species 

 of Ennoiia, which have been found only in Senegambia 

 and Guiana, together with Amphidiscus od/usus, also 

 South American. The only new species was Eicnotia 

 longicornzs, which is very similar to a Hungarian 

 fossil species. No species peculiarly African was 

 found in the dust ; one occurs in the Isle of France. 



Of a shower which fell at Malta, May 15, 1830, 

 the dust was obtained by Darwin, from the purser 

 of the Revenge. The wind at the time was east- 

 south-east, and a similar fall of dust took place at 

 the time in the bay of Palmas, in Sardinia. The 

 number of species afforded was forty-three. Some of 

 the species occur in Africa, yet there are no charac- 

 teristic African forms. And although such showers, 

 with the hot winds that attend them, are usually 

 referred to the Sahara desert, they appear to be quite 

 foreign to that region. Among the species Synedra 

 entovwn is a characteristic form from Chili. In 

 general character the species are like those of the 

 Cape Verde and other Atlantic showers. 



In the sirocco dust of Genoa, May 16, i8z|.6, 

 Ehrenberg found forty-six species. The forms have 

 much resemblance to those of the Malta and Atlantic 



