54 THE AMERICAN MONTHLY [Feb 



a very interesting earth. It is white, almost like chalk, 

 not calcareous but siliceous and found in Arizona. Un- 

 der the microscope, it appears made up entirely of frus- 

 tules of Bacillaria (an older word than Diatomacea). 

 Whether marine or fresh- water the microscope alone can 

 determine. It consists largely of rather large discs very 

 beautiful in form and which look like Actinocyclus, but 

 are Cyclotella. This genus contains both marine and 

 fresh-water forms. When examined closely I found it to 

 be the same as certain specimens from theN. W. Bound- 

 ary Survey (1870). See Am. Jour. Science, 1891, "On 

 the Infusorial Earths of the Pacific Coast." In my paper 

 on the DiatomacesB of the Geological Survey of Cali- 

 fornia, I called it Cyclotella pulcherima on account of its 

 beauty. I now consider it only a form of Cylcotella bero- 

 linensis, C. Gr. E. which was found in Berlin years ago. 

 Being found at Niagara it was called Stephanodiscus ni- 

 agarse C. G. E. I have living specimens of it from 

 Lake Erie. It shows how forms may be modified in pass- 

 ing from fresh-water to brackish and to salt where it be- 

 comes Actinocyclus. 



Species as commonly known do not exist in Nature but 

 forms do. Forms are changeable until they merge one 

 into another or fade out. As forms change so genera 

 change. One genus changes into another and one family 

 may merge in the next. Hence forms can be placed with 

 difficulty at times. They may be Bacillarian, Radiolarian 

 or Sponge. 



Actinocyclus is common in guano at Ichaboc, Africa, 

 and on every coast of the sea. It is found fossil in the 

 clay of Hatfield swamp, N. J., in the Pasaic river, and in 

 the drinking water of Paterson, N. J. There it is called 

 A. ralfsii. Ehrenberg first described it in 1845 (Bericht. 

 Berlin Akademie) as Stephanodiscus brolinensis. Found 

 in the Nile, it was called S. segyptiacus; at Canton, S. 

 sinensis; in the Ganges, S. bramaputrse and here as S. 



