Flagellates with two flagella, of which one is directed forwards and
is concerned with the locomotion of the animal, while the other is
directed backwards and drags after the animal when in motion. Body
slightly compressed dorso-ventrally (fig. 17, section). An oral
furrow is present on the ventral side and the two flagella originate
in it (fig. 17, at left). The vacuole is on the left side. Food
vacuoles are present in the posterior part. The nucleus is central.
Movement creeping.
Fresh and salt water.
Anisonema vitrea (Duj.) Fig. 17.
Synonyms: _Tropidoscyphus octocostatus_ Stein '83; _Sphenomonas_ Kent
'81; _Ploeotia vitrea_ Senn 1900.
With the characteristics of the genus. It differs from freshwater
forms in having eight furrowed surfaces running somewhat spirally
from the posterior to the oral end. Length 50µ; width 23µ. This
attractive flagellate was quite common in decaying algæ at Woods
Hole; its shaking movement, its peculiar furrowed surfaces, and,
above all, its perfectly transparent, vitreous appearance, were well
described by Dujardin. Stein's _Tropidoscyphus octocostatus_ is a
fresh-water form which may possibly be a distinct species, especially
as it is described with both flagella directed forwards.
[Illustration: Fig. 17.--_Anisonema vitrea_.]
Genus DISTEPHANUS Stöhr.
An aberrant flagellate bearing a single flagellum and a silicious
skeleton resembling those of the Radiolaria. The skeleton consists
of two rings of different diameter parallel with one another and
connected by silicious bars. From the wider ring half a dozen bars
radiate outwards and a similar number of short thorn-like bars point
inwards obliquely. The color is yellow, and except for the flagellum
the form might easily be mistaken for a Radiolarian, as has been the
case repeatedly.
Distephanus speculum Stöhr.
_Dictyocha speculum_ Stöhr; _Dictyocha_ Auc.
With the characters of the genus.
A single specimen only of this very interesting form was seen at
Woods Hole. It occurred in a collection of tow made near the end of
the wharf during the evening.