Sketch of the Infusoria of the family Bocitlaria. 291 
There has been much discussion as to the real nature of the 
bodies in flint which so closely resemble the recent Xanthidia ; 
Turpin mistook theny for eggs of Cristatella, to which however 
they have but little resemblance. Ehrenberg gives figures in his 
small treatise, ‘die Fossilen Infusorien und die lebendige Dam- 
merde,” Pl. 1, figs. 2, 12 to 17, which show the closest resem- 
blance between the recent and the fossil species. It is remarka- 
ble however that the recent species are inhabitants of fresh water, 
while flint is undoubtedly of marine origin. I have not seen dis- 
tinct motion in any of our species. 
‘ ol. Xanthidium 2 ramosum. Corpuscles globular, separate or binary, 
spines scattered, terminated in three or more points 5/5 to sy line. Fos- 
sil in gun flints. 
2. Xanthidium (Fig. 15, Pl. 1.) Binary, each portion 
having numerous rather long arms terminating in three diverging points. 
_ This very beautiful American species is, when living, of a fine 
gteen color. Its carapace is hard and apparently siliceous, as it 
retains its form in spite of the action of fire and acids. _ Every 
living specimen of this species which I have seen, has been com- 
posed of two symmetrical portions, as shown in the figure. These 
bodies when in the position shown in the figure, have much re- 
semblance to Ehrenberg’s drawings illustrating the Spontaneous 
division of some of the species. When thrown into other posi- 
tions, so that the line of union of the two portions is not seen, it 
may easily be mistaken for a simple spherical body bristling with 
atms. The two portions often separate after death, and may 
then be mistaken for individuals resulting from spontaneous di- 
Vision, but by throwing them into various positions by means of 
@ compressor, the orifice corresponding to the line of separation 
of the two original parts may always be seen. The same re 
Will apply to the next species also. ; 
It ocenrs not unfrequently in a subalpine pond a few miles 
from West Point; it is also occasionally found in ditches, in peat 
3. -Kalthidten (Fig. 16,.a, 5, Pl. 1.) Binary, each por- 
tion somewhat triangular and terminating at each angle in three short, 
tiverging arms, each having three small diverging points. 
The smaller size and triangular form of these bodies, make me 
think them of a different species from the preceding. I have not 
Seen any intermediate forms, although they oceur together in 
about equal abundance at the above mentioned locality. 
