BIOLOGY. ae 
solvable by a 1-4, central light—something very exceptional in that genus, which 
are usually so finely marked as to be among our most difficult test objects, and 
usually unresolvable by almost any power and central light. 
There was a great abundance of fine Surirell@, mostly tenera, splendida, 
or varieties, which are among the largest diatoms in that genus. Also, another 
much longer but narrow, like fig. 8 of Schmidt’s Atlas, pl. XXIII, one of the 
largest Surirelle, and a very unusual form, not found at Cincinnati, Gage’s 
pond, or Silver Lake. (See fig. 13, pl. II.) 
The smaller forms, too, were very numerous and interesting, and included 
many, especially several small, oval Navicul@, which could not be recognized 
from any of the authorities at hand, and were perhaps new. As is usual, 
Navicula was the most abundant form as to species, though by no means as to 
individuals. 
One of the features of these Medora slides was the almost entire absence of 
Gomphonema, as noticed also in eastern Kansas—one of the most abundant 
forms everywhere else, and so abundant at Cincinnati that many slides of the 
forty-four mounted there contain hardly anything else; but they were so scarce 
at Medora that I was inclined for some time to think them altogether absent; 
though I eventually succeeded in finding several in the five slides, almost all of 
different species. 
Melosira, a very abundant genus at Cincinnati, was altogether absent at 
Medora. Cocconeis, a very common form, especially pedicuius, was not ob- 
served in the Medora slides nor at Gage’s pond nor Silver Lake, though there 
was one in the stomach of the little fish caught at Belvidere. Only one indi- 
vidual of Meridion was met with, and only one Synedra, which at Cincinnati 
was the second most abundant form, Nitzschia being first. 
There are usually Plewrosigme in almost every gathering made anywhere; 
and there were plenty at Belvidere, not far away; but, very curiously, not a single 
one could be found in these Medora slides. 
Cymbella is usually a very abundant form everywhere, almost as much so as 
Gomphonema, it being present at Cincinnati in the proportion of eighty to 
eighty-eight of the latter; but it was so rare at Medora as to be seldom seen. 
Eunotie, common at Cincinnati, were entirely absent in Kansas, none having 
been found at Gage’s pond, Silver Lake, or Medora. 
I know not how to account for the almost entire absence of these forms so 
universally abundant in the Eastern states and the central West, unless we suppose 
it to be due to the only abnormal condition present, so far as known to me; that 
is, to salt or alkali, especially the latter, which whitens the surface around the 
marshes in that section whenever the water goes down. 
There are several curious unrecognizable pieces found in the five slides. One, 
of them resembled part of a shell, apparently. The central half rose up in a 
boss or swelling, surrounded by a flat surface covered with irregular wavy lines. 
There were a good many cylindrical pieces, appearing under a 1-10 to be about 
an inch or an inch and a quarter long, and an eighth of an inch or a little more 
in diameter; very rough outside. No fresh-water sponge spicules were seen, 
which I should otherwise have been inclined to connect them with, and it was 
impossible to tell just what they were. 
A second piece (fig. 11, plate II),a round, saucer-shaped disk, I at first thought 
a Coscinodiscus, common in salt water, but of which there is only one repre- 
sented in fresh water, C. lacustris, of which one individual was found in the 
forty-four Cincinnati slides; but which is very rare. The central part was re- 
ticulated in hexagons like honeycomb. It was so dishing I could not get enough 
