th 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.

Exuviaella lima Ehr. Fig. 18.

Synonyms _Pyxidicula_ Ehr.; _Cryptomonas_ Ehr.; _Prorocentrum lima_
Kent; _Amphidinium_ Pouchet.

The shell is ovate, rounded and swollen posteriorly. The anterior
border of both shells is slightly indent