1901] MICROSCOPICAL JOURNAL. 265 
could, without any crowding whatever, be placed in a cir- 
cle of that size. | 
To give an idea of the rarity of Hpithemia gibba at 
other places, I may say that, in the forty-four slides from 
which my catalogue of the Cincinnati Diatomaces was 
drawn up, representing about thirty different gatherings, 
this diatom is found in only two of them. In a very re- 
markable gathering I made from the Fox river, at Elgin, 
Ill., a half-inch mount of which contained ninety-four 
recognized species, only two Hpithemia gibba were ob- 
served, and in one from a pond in Oakwood park, Elgin, 
none ; nor were there any in fine gatherings made at 
places so widely scattered and generally representative 
of the West and South as Lake Geneva, Wis., Hailey’s 
Springs, Idaho, or Calera, Ala. There were none in a 
gathering I made from the Chicago water-supply, though 
it is catalogued in Thomas and Chase’s Diatomacea of 
Lake Michigan, from which the city water-supply is de- 
rived. Two fine gatherings made in northeastern Ohio, 
near Ashtabula, contained noH#pithemia gibba. A gather- 
ing made early in October from the fountain basin on 
Twelfth street, two or three blocks southwest of the capi- 
tol, in Topeka, contained hardly anything else but this 
Epithemia; so that its abundance here seems to be a re- 
markable peculiarity of this locality, depending, perhaps, 
on some constituent of the water-supply unusually favor- 
able to it. If so, it must, I imagine, be derived from 
the Republican branch of the river, as a gathering I made 
from the Blue at Beatrice, Neb., last year, contained none 
of this diatom. | 
In connection with Amphipleura pellucida, mentioned 
above, itis not only very rare, but is placed at the end of 
Moller’s test plate as the most difficult test object known 
to microscopists, and is stated in scientific text-books to 
be the smallest regularly organized thing known. Of 
course, the delicate markings referred to below are not 
