68 KANSAS ACADEMY OF SCIENCE. 
To give an idea of the rarity of Epithemia gibba at other places, I may say 
that, in the forty-four slides from which my catalogue of the Cincinnati Diato- 
maces was drawn up, representing about thirty different gatherings, this diatom 
is found in only twoof them. Ina very remarkable gathering I made from the 
Fox river, at Elgin, Ill., a half-inch mount of which contained ninety-four recog- 
nized species, only two Hpithemia gibba were observed, 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 Diatomacex of Lake Michigan, from which the city water- 
supply is derived. Two fine gatherings made in northeastern Ohio, near Ashta- 
bula, contained no Hpithemia gibba. A gathering 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 remarkable peculiarity of this locality, depending, 
perhaps, on some constituent of the water-supply unusually favorable 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, it is 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. The figure I give (fig. 30, pl. III) is 
not very satisfactory, but may serve to convey an idea of it. Of course, the deli- 
cate markings referred to below are not visible at 775 diameters, and the lines 
across the middle are merely a very coarse imitation of them, to show their direc- 
tion, etc. 
Mr. Patrick informed me that he very carefully examined the alga the 
Amphipleura was growing on and found it to be Cladaphora fracta Kg., 
which I believe only grew over a small space on the east and north walls, a fact 
very interesting, as showing that it is probably parasitic on this alga, and only 
found in connection with it, something not before observed, so far as known to 
me. This would account for its not being found under the lily-pads, or at the 
south end, where this alga did not grow. The rarity of this diatom may be due 
to the fact that this alga does not grow everywhere. 
As possessing possible interest, I may say that I once measured Amphipleura 
pellucida by a Rogers stage micrometer, and found it not quite one two-hun- 
dredths of an inch in length. The smallest grains of ordinary sand which can be 
picked up with a pair of watchmaker’s tweezers and arranged as close together 
as possible under a magnifying glass go only sixty-four to an inch, so that the 
length of this diatom is only a little over one-quarter of the diameter of one of 
the finest grains of sand; yet in this short length it is marked with 340 of the 
finest and most regular lines ever seen ruled across it, and each line apparently 
composed of rows of beads. I counted these lines on an excellent photograph of 
it, by Doctor Detmers. A list of the genera and species found at Gage’s pond is 
as follows: : . 
Achnanthes minutissima. Cocconema cistula. 
Amphipleura pellucida. Cocconema lanceolatum. 
Amphora libyca. Cocconema mexicanum. 
Ampbhora ovalis. Cocconema (a large unknown, perhaps 
Cocconema australicum. new). 
