26 Dr C. G. Ehrenberg on the Infusoria and other 



there are no characteristic 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 

 entomon is a characteristic form from Chili. In general cha- 

 racter, the species are like those of the Cape Verd and other 

 showers. 



IV. Sirocco dust of Genoa, May 16, 1846. — In this dust, 

 Ehrenberg found 22 species of Polygastrica, 21 of Phyto- 

 litharia, and 3 of parts of plants. The forms have much re- 

 semblance to those of the Malta and Atlantic showers. The 

 colour is yellowish or ochreous, from oxide of iron, and not 

 grey like the true African dust, and about one-sixth to one- 

 third of the mass is organic. None of the species are charac- 

 teristic African forms, and Synedra entomon is South Ame- 

 rican. 



It follows from the preceding results that the showers of 

 the Atlantic, of Malta and of Genoa, are in general alike, in 

 organic, as well as inorganic constitution, and in the absence 

 of characteristic African forms ; and this resemblance is the 

 more surprising, as the observations extend through the long 

 period of 16 years, from 1830 to 1846. They are alike, also, 

 in the brownish red colour of the dust. 



V. Sirocco dust of Lyons, Oct. 17, 1846. — The Lyons 

 shower afforded 39 species of Polygastrica, 25 of Phytolith- 

 aria, 3 of Polythalamia, besides minute portions of plants. 

 In this shower, the organic forms make up about one-eighth 

 of the mass. In general character, including colour, there 

 is a close resemblance to the products of the Atlantic showers 

 and the others above described. The species are nearly all 

 of fresh-water or land origin ; one-seventh only are marine 

 species. The most abundant forms of Polygastrica are Eu- 

 notia amphioxys, E. gibberula, E. longic6rnis, Gallionella 

 decitssata, G. granulata, and G. procera ; and those of Phyto- 

 litharia, Lithostylidium Amphiodon, L. ossiculum, and L. rude. 



There are two South American species, the Eunotia Pileus 

 and Himantidium Zygodon. 



The number of species brought to light from the dust of 

 nine showers thus far described, is as follows : — 



