310 T. a. o'doxohoe on pin nul aria nobilis. 



must call the costae, broken up into three parts, with very fine 

 lines between them. It may be seen that the middle parts of 

 the costae are in the sharpest focus because they represent the 

 highest of three distinct planes. Now if this interpretation be 

 correct, the structure of this diatom is very complex, as there 

 would be three planes on each side of the raphe, and the planes 

 on the one side would coincide with those on the other only when 

 the diatom was perfectly flat on the cover-glass a very un- 

 likely case. 



I now tried to resolve the costae, with the result as shown 

 [here an image was projected on the screen], which reminds one 

 of the bones of a skeleton's hand. 



There remained the resolution of the very fine lines between 

 the costae, probably into dots. After trying to do this many 

 hours without any success I substituted Mr. Akehurst's dark- 

 ground condenser for the Holoscopic, with the result that, after 

 considerable manipulation I was able to get the photograph here 

 reproduced. (See PI. 22, fig. 2.) This shows at least partial 

 resolution on both sides of the raphe. 



Journ. Quekett Microscopical Club, Ser. 2, Vol. XII., No. 74, April 1914. 



