[Illustration:  Fig. 31.—­Side and top views of Mesodinium cinctum.]

Genus TIARINA R. S. Bergh ’79.

(Claparede & 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; Moebius ’88,
Lauterborn ’94; Shevyakov ’86.

This form, which resembles Coleps rather closely, was placed as a separate genus by R. S. Bergh.  The skeletal parts consist of five zones of needles composed of an organized substance and embedded in the cortical plasm, the last zone coming to a point at the posterior end.  The needles have lateral processes, which give a latticed appearance to the casing.  The cilia are long, with a specialized crown of still longer ones at the oral end; they arise outside of the skeletal elements and do not pass between them, as in Coleps.

KEY TO MARINE GENERA OF TRACHELINIDAE.

Diagnostic characters:  Body bilateral, or asymmetrical by local prolongations; usually compressed or flattened laterally, the left side more convex than the right.  The essential feature is the position and character of the mouth.  This is either a long slit extending from the anterior end well down the ventral surface, or the posterior part only of a ventral furrow remains open as a round or elongate mouth some distance from the anterior end.  The entire mouth region of the body is usually drawn out into an elongate tapering proboscis which is generally curved dorsally at the extremity.  An oesophagus is short or absent altogether; when present it is supported by a stiff buccal armature.  Cilia are uniform about entire body or limited to the flat right side.  Food is swallowed.

1. a.  Proboscis easily distinguished 2
      from the main body

   b.  Proboscis not marked off from Genus *_Loxophyllum_
      main body; body flat;
      both surfaces striated

2. a.  Mouth runs the entire length Genus Amphileptus
      of proboscis; entire body
      uniformly ciliated

   b.  Mouth runs the entire length Genus *_Lionotus_
      of proboscis; body flat; right
      side only is ciliated

   c.  Proboscis much drawn out, Genus Dileptus
      flexible; mouth at its base

   * Presence at Woods Hole indicated by asterisk.

Genus LOXOPHYLLUM Dujardin ’41.

(Duj. ’41; Wrzesniowski ’69; Quennerstedt ’65; ’67; Cohn ’66; Entz ’84; Gourret & Roeser ’88; Buetschli ’88; Shevyakov ’96.)