The chief features by which this species is distinguished from the
frequently described _M. pulex_ of Europe are the number of anterior
cirri and the ring of true cilia in place of the central girdle of
cirri. The European form is described with four anterior bristles;
the present form has from 28 to 32. The radial cilia differ decidedly
from the more powerful cirri and they are not in one plane, so that
counting is difficult; they are not closely set. The presence of
tentacles makes these forms of especial theoretical interest,
especially in the light of the origin of _Suctoria_.


[Illustration: Fig. 31.--Side and top views of _Mesodinium cinctum_.]


Genus TIARINA R. S. Bergh '79.

(Claparède & Lachmann '58.)

Body subcylindrical, pointed posteriorly, two and one-half times
as long as broad; encased in covering composed of separate pieces
arranged in five girdles. The pieces bear processes which rest
against neighboring pieces of the girdle. Mouth large, anus terminal
near contractile vacuole. The macronucleus is simple and round. Salt
water.


Tiarina fusus (Cl. & Lach.) emend R. S. Bergh.

Synonyms: _Coleps fusus_ Cl. & Lach. '58; Daday '86; Möbius '88,