Ehrenberg on Infusoria in Igneous Rocks. 409 



6. There are at this time ninety-four different species of micros- 

 copic bodies recognised as forming an integral part of the Rhenish 

 volcanic tuff ; and of these seventy-two are Polygastrica and twenty- 

 two Phytolitharia, and all without exception consist of land or fresh- 

 water forms. Only four or five of the whole number are unknown 

 and peculiar. 



7. With regard to the particular species, the author remarks that 

 the toothed Eunotice, viz. Eunotia triodon (having three teeth) and 

 E. Diadema (with six teeth), have not hitherto been met with by 

 him in a living state in Germany, and are generally considered as 

 northern fossil forms in Sweden, Finland and North America. The 

 first of them was however found living near Salzburg by the late Dr. 

 Werneck, and has recently been recognised in atmospheric dust 

 from the Cape de Verd Islands. There are also three species of Bi~ 

 blaria not now known to exist in Europe. 



8. Among those whose remains form great masses in the Rhine 

 district may be enumerated Discoplea eomta and Pinnularia viridula. 

 The first is only at present known as an existing species on the 

 high lands of Koordistan, but the other is common in a living state 

 every where in the vicinity. The Discoplea occurs also in the pho- 

 nolitic incrustation of Hochsimmer and at Wistershan in Bohemia, 

 and is also present in the ashes which have buried the ancient city 

 of Pompeii ; and a very similar species is found in the tertiary tripoli 

 of Virginia ; it is closely allied to Gaillonella crenulata. 



The author mentions that he has seen and carefully avoided errors 

 of observation arising from the resemblance of some forms of infu- 

 sorial cases to fragments of crystalline bodies, such as sodalite and 

 leucite, which are often present, and might readily be the cause of 

 mistaken descriptions. 



9. If, after a further extension of our knowledge as to the circum- 

 stances of the case at Hochsimmer, it should appear possible that 

 this deposit might have been formed by a shower of ashes, or by 

 projectiles consisting of a fine dust fused together into a mass with- 

 out the presence of moisture, such showers occurring at intervals and 

 after the lapse of short periods of time ; or if the local conditions 

 should require that such ashes have been driven by a steady wind 

 into a dry crater-shaped hollow, where they have been received and 



