On Infusoria in Dust-showers and Blood-rain. 373 
lay under the field of his microscope, exhibiting to the eye the 
relative prevalence of different forms and the colors they present- 
e e showers, whose microscopic org@nisms are here report- 
ed, are as follows: : 
I. In the Atlantic, latitude 17° 43' N., and longitude 26° W., 
about 500 miles from the coast of Africa.—The dust was col- 
lected by Mr. Darwin, from the ship in which he was at the time. 
The direction of the wind was from the African coast. The 
dust resembled volcanic ashes, although evidently not of this 
origin, and about a sixth part of it was siliceous shells of fresh 
water and land infusoria and siliceous phytolites, eighteen species 
of the former, and as many of the latter: The most of the forms 
ers is given in a following table. 
ther dust-showers in the Atlantic, from the collections of 
Mr. Darwin.—These collections were made between the years 
1834 and 1838, in latitudes 15°, 17°, 19° and 21°, part at San 
Jazo, (Cape Verds) and part within 250 miles of the land in 
the open sea, between longitudes 22° and 26°. ‘They afford 
thirty new forms to those of the shower above noticed, and in- 
clude also the same South American forms, Himantidium papilio 
and Surirella peruviana. In addition, there are three species 
of Eunotia which have been found only in Senegambia and 
Besides the others, there was one Polythalamium, making 
Cs 
1830.—This 
