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