Colorless forms of medium size-in some cases they may be green by Zoochlorella. The general structure is similar to that of _Vorticella_, but the individuals are elongate and occupy houses. The macronucleus is invariably long and band-form. The distinguishing character is the colorless or brownish lorica of quite variable form but always attached. These houses may be finger-formed, with widened center, or widened mouth, or constricted mouth, and the like. Ring-formed swellings are frequently developed. Sometimes the mouth becomes twisted and the lorica is therefore bilateral. The houses are attached either directly to some foreign object or by means of a short stalk. The animals are similarly fastened to the lorica, sometimes directly, sometimes by means of a short stalk. When they contract they draw back to the bottom of the lorica; when expanded they usually stretch out of the mouth opening. In some forms there is an operculum, by means of which the opening of the shell can be closed when the animal is retracted. Fresh and salt water. The number of species of _Cothurnia_ has become so great that the difficulty in placing forms is almost sufficient to discourage the systematist; as Bütschli well remarks, the variations in the theca have been made the basis of new species so many times that the genus is almost as confused as _Difflugia_ among the rhizopods or _Campanularia_ among the hydroids. The length of cup, of stalk, the presence of annulations on stalk or cup, etc., have given rise to many specific names, the majority of which I believe can be discarded. According to such differentials the same branch of an alga holding a hundred specimens of _Cothurnia crystallina_ yield 10 or 12 species, whereas they 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_ Claparède & 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 70µ to 200µ (_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.