196 KANSAS CITY REVIEW OF SCIENCE. 
is so slow and slight that it proves so little as to have scarcely any weight in the 
discussion. Let us notice a few in detail. 
Take one of the lowest, Pusulina Cylindrica, a small Rhizopod, in appear- 
ance like a grain of barley. It has a wide geographical as well as geological 
range. It is found in Europe, Asia and America,and from the Sub-carboniferous 
through the Permian, or in one-eighth of the /fossdsferous age of the globe. It 
has a series of coils, like the Nautilus, with septa, or partitions, extending part 
way across the chamber, instead of wholly, asin the Nautilus and Ammonite.* 
These chambered shells are far higher in rank than this little half chambered 
shell. Yet during all its long geological life of six million years, it never extend- 
ed its partition entirely from coil to coil, to take the first step toward a higher 
form. 
Take another characteristic species of the Carboniferous Age, of a higher 
order—Athyris Subtilita. It is exceedingly abundant in America, as well as in 
Europe, in all the carboniferous deposits. It also, unlike the Fusulima, has a 
tendency to sport under a variety of forms (hence its name), but always keeps 
within a prescribed boundary. Thus a quantity of specimens from the same 
locality, say the lowest, will vary so much, that the extremes being taken, without 
reference to the intermediate forms, two species would be recognized. Another 
quantity from a different region, and entirely different horizon, perhaps the 
highest, will disclose a like variable appearance, but in no greater degree. If the 
two collections are then placed side by side, one cannot be distinguished from the 
other. No two will be found alike, but all are Athyris Subtilita. ‘Though varia- 
bility is always a feature of this shell, it constantly retains its specific character_ 
istics, within a narrow circle of vitality, from the lowest Carboniferous through 
the Permian. 
In contrast, as far as versatility is concerned, and of persistence in details, 
we may take another common carboniferous species, viz., roductus semi-Retic- 
wlatus. It, like the others, runs through that entire geological age. It derives its 
name from the reticulation, or crossing lines, of the outer surface of the upper 
half of the ventral valve of the shell.{ So little change occurs in its structure, 
during all its existence, one-eighth of the geological history, that the simple small 
furrows did not disappear from one half, or extend over the other half, in millions 
of generations. Is evolution a law of natural history when it is so persistent in 
small things ? 
Passing to another order of Mollusks, let us examine the Os¢vea, or oysters. 
They date from the Paleozoic§ Age. Like the Athyris Subtiita, the whole genus 
is noted for its sporting variation of outline, and for an equal adherence to its 
original characteristic phases. Its peculiar foliated texture of shell, too well known 
to need description, the irregularity in shape and curvature of the valves, and the 
*See note on page 21. 
{See Fig. Dana’s Manual. 
*Paleozoic includes the three divisions, Silurian, Devonian, and Carboniferous. 
2See Fig. Dana’s Manual. 
