Anterior part with 3 equatorial Genus *_Ceratium_
      and no rhombic plates

   9.  Anterior part with 14 equatorial Genus Pyrophacus
      and 1 rhombic plates

      Anterior part with 7 equatorial Genus Goniodoma
      plates

      Anterior part with 4 equatorial Genus Amphidoma
      plates

  10.  Apical extremity drawn out Genus Podolampas
      into a tube

      Apical extremity not drawn out Genus Blepharocysta
      into a tube

  11.  Cross-furrow deep, with great Genus Ceratocorys
      ledge-like walls

      Cross-furrow wide, no ledge-like Genus Oxytoxum
      walls

   * Presence at Woods Hole indicated by asterisk.

KEY TO MARINE GENERA OF DINOPHYSIDAE.

Diagnostic characters:  The cross-furrow is above the center of the body, and its edges, as well as the left edge of the longitudinal furrow, are usually produced into characteristic ledges; those of the cross-furrow usually form great funnel-like anterior processes, while those of the longitudinal furrow usually form great, lateral, wing-like processes ornamented by ribs and other markings.

   1.  Without shell; longitudinal Genus *_Amphidinium_
      furrow may open & close

   2.  With shell; longitudinal furrow 3
      unchangeable

   3.  With distinct apical funnel 4

      No apical funnel Genus Phalacroma

   4.  With great wing-like ledge 5

      Ledges very small; body long, Genus Amphisolenia
      needle-like

   5.  Ledge of longitudinal furrow 6
      extends to posterior end

Ledge of longitudinal furrow Genus Dinophysis does not extend to posterior end (Recorded by Peck (’93-’95) as very abundant at Woods Hole and in Buzzards Bay.)

   6.  Ledge is continued dorsally to Genus Ornithocercus
      the cross-furrow

      Ledge is not continued dorsally 7

   7.  With deep dorsal cavity; Genus Citharistes
      secondary funnel not notched

      No dorsal cavity; secondary Genus Histioneis
      funnel deeply notched

   * Presence at Woods Hole indicated by asterisk.

Genus EXUVIAELLA Cienkowsky ’82.

(Klebs ’81; Pouchet ’83, ’86.)

The form varies from globular to ovoid, with occasionally a sharp posterior end.  Shells are usually somewhat compressed, and consist of two valves, which frequently slide one over the other in such a manner as to show the structure with great clearness.  The right shell may have a distinct indentation in the anterior edge.  There are two lateral, discoid, brown chromatophores, each of which possesses a central amylum granule.  The nucleus is posterior.  Salt water.