Microscopic Forms in Dust-showers and Blood-rain. 25 



they presented. The showers, whose microscopic organisms 

 are here reported, are as follows : — 



I. In the Atlantic, latitude 17° 43' iV., 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 silicious shells 

 of fresh water and land infusoria, and silicious phytolites, — 

 eighteen species of the former, and as many of the latter. 

 The most of the forms are European, and none exclusively 

 African. - Among them there is the South American species 

 Himantidium papilio, which occurs at Cayenne, and also a 

 Surirella, probably from the same continent. The conclusion 

 follows, as Ehrenberg observes, that either the dust came in 

 part from South America, in the upper regions of the atmo- 

 sphere, or these two species are yet to be discovered elsewhere. 



II. Other Dust-shorcers in the Atlantic, from the Collections of 

 Mr Darrvin. — These collections were made between the years 

 1834 and 1838, in latitudes 15°, 17°, 19°, and 21°, part at San 

 Jago (Cape Verds),and part within 250 miles of the land, in the 

 open sea, between longitudes 22° and 2^°. They aiford thirty 

 new forms to those of the shower above noticed, and include 

 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 

 Guiana, together with the Amphidiscus obtusus, also South 

 American. Besides the others, there was one Polythalamium, 

 making in all 67 organic forms. The only new species was the 

 Eunotia longicornis, \w\)ic\\ is very similar to a Hungarian fossil 

 species. No species peculiarly African was found in the dust. 

 One, the Lithostylidium Bajula, occurs at the Isle of France. 



III. Dust which fell at Malta, Ibth of May 1830. — This 

 dust was obtained by Mr Darwin from purser R. G. Didham, 

 of the ship 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 43, of which 15 were Infusorial, 21 Phytolitharia, and 

 7 Polythalamia. Some of the species occm* in Africa, yet 



