are merely growth stages of one and the same
form.

Cothurnia crystallina Ehr. Fig. 62.

Synonyms: _Vaginicolla crystallina_ Ehr., Perty, Eichwald; _V.
grandis_ Perty; _V. pedunculata_ Eichwald; _Cothurnia crystallina_
Claparede & Lachmann, D'Udek.; _C. gigantea_ D'Udek; _C. maritima_,
_C. crystallina_ Cohn; _C. grandis_ Meresch.

The form of the cup shows the greatest differences; sometimes it is
cylindrical, sometimes elongate thimble-shape, sometimes pouch-shape,
corrugated or smooth on the sides, and wavy or smooth on border.
Frequently the basal part becomes stalk-like, but this is very short.
When present, the stalk may or may not have a knob-like swelling. The
animal within the cup may or may not be borne on a stalk, and this
stalk may or may not be knobbed. The cups are colorless or brown. The
animal is very contractile and may stretch half its length out of the
cup or retract well into it. There is no operculum. The length of the
cup varies from 70 mu to 200 mu (_C. gigantea_; _Vag. grandis_, etc.).
From Entz.

There is nothing to add to Entz's characterization of this species,
which is found both in fresh and salt water. The variability of the
cup and stalk is quite noticeable in the Woods Hole forms.

[Illustration: Fig. 62.--_Cothurnia crystallina_.]

Cothurnia imberbis Ehrenberg, var. curvula Entz. Fig. 63.

Synonyms: _C. imberbis_ Kent et al.; _C. curvula_ Entz; _C. socialis_
Gruber?

The lorica is swollen posteriorly, narrowest at the oral margin, bent
on its axis and is supported on a short stalk. It is perfectly smooth
and without annulations. The animal itself has no definite stalk.
When fully expanded the animal emerges but slightly from the margin
of the cup. Fresh and salt water. On red algae. Dimensions of Woods
Hole form: Cup 50 to 55 mu long; greatest diameter 22 mu; length of stalk
4 to 5 mu.

[Illustration: Fig. 63.--_Cothurnia imberbis_.]

Cothurnia nodosa Claparede & Lachmann. Fig.64.

A. Smooth cup.--_Cothurnia maritima_ Ehr., Eichwald, Stein, Kent.

B. Cross-ringed cup.--_C. pupa_ Eichwald, Stein, Cohn; _C. nodosa_
Cl & L.; _V. crystallina_ Entz '78; _C. pontica_ Meresch.,
Kent; _C. cohnii_ and _pupa_ Kent; _C. longipes_ Kellicott '94.

The cup is elongated, swollen centrally, tapering at oral end
and conical at base or rounded. Oral opening either circular or
elliptical. Cross rings may or may not be present, and the cup is
either smooth or a