The ventral surface is flat and has two excavations in the posterior
end. The right hollow is larger and contains 5 great cirri of unequal
size, the extreme right one being the largest. The left hollow
contains 2 cirri, also of dissimilar size. Dorsal to the 5 right
cirri are 3 sickle-formed cirri, which are usually fimbriated. These
are pointed and curve regularly to the left. The peristome is wide
and open, and a small pocket-like hollow on its left border indicates
the region of the mouth. The adoral zone runs into this pocket
and the mouth is located in its lower right-hand corner. In _U.
transfuga_ the right border is generally described as having a
membrane of extreme delicacy. I was unable to see such a membrane in
this form, but in its place there are 2 flagella-like cirri extending
from the margin of the mouth-opening into the peristome, and these
vibrate slowly. I do not believe these could be the moving edge of an
undulating membrane, for they are quite distinct. The macronucleus is
spherical instead of band-form, and a single micronucleus is closely
attached. This is unlike the European species _U. transfuga_, in
which the nucleus is elongate. The contractile vacuole lies between
the two sets of posterior cirri. There are no marginal folds like
those of the European species.

Length 40µ; width 25µ. Common.


[Illustration: Fig. 55.--_Uronychia setigera_.]


Genus ASPIDISCA Ehr. 1830.

(Perty '52; Cl & Lach. '58; Stein '59; Quennerstedt '65, '67, '69;