572 MICROSCOPY. 
Argus being composed of radiating bands of minute and closely 
packed spherules with intervening rows of clusters of larger 
spherules usually in fours, and Jsthmia enervis revealing, in the 
place of its familiar reticulated appearance, an aggregation of 
minute spherules at different levels but of, as yet, not well deter- 
mined arrangement. A Beck’s + objective will reveal this struct- 
ure, though a 4 is preferable; Powell and Lealand’s new pattern 
(dry front) giving it excellently. 
On the other hand, Mr. Samuel Wells of Boston, who has stud- 
ied Eupodiscus Argus without the reflex illuminator, perceives no 
spherules and explains the usual appearances without them. The 
outer or convex surface he finds clear and smooth, except that it 
is irregularly dotted with depressions about şọ%oinch in diameter 
and extending nearly through the thickness of the valve. This 
appearance is verified by the binocular microscope and by sec- 
tional views obtained from broken valves, and is not varied by any 
change of power or illumination. The concave surface, which 
Moller mounts upwards and which alone was probably studied by 
Mr. Slack, is nearly smooth, without ridges and probably without 
granulation. It is covered with irregularly radiating rows of 
round dots with intervening blank spaces. These dots are about 
sobos inch in diameter, and with a ;, or sẹ and Prof. H. L. 
Smith’s apparatus for opaque illumination, they appear to be slight 
depressions with the bottom slightly convex; the four or more 
which are over each of the depressions on the other side of the 
valve being naturally brighter than the others, and corresponding 
to the groups of larger spherules of Mr. Slack. 
Mr. Charles Stodder also combats the doctrine that the silicious 
matter in diatoms is always deposited in the spheroidal form. He 
still believes that the markings on ordinary diatoms are depres- 
sions and not elevations, and that the line of fracture is inclined 
to run through them instead of between them, and he therefore 
retains the terms “ cellules,” “ areolæ,” etc. His account of Eu- 
podiscus Argus is so much like that of Mr. Wells, though published 
independently, as to suggest the explanation that they have - 
worked at the subject together. He finds two silicious coats, the 
outer comparatively opaque and marked with large, thin apertures 
through which could be seen the inner coat with its much finer 
markings which vary according to focus and illumination from ® 
spherical to a cellular appearance, and from a radiated to an irreg- 
