Part 6 (1/2)

KEY TO FAMILIES OF DINOFLAGELLIDIA.

1. No crossfurrow; two free flagella Family _Prorocentridae_

2. One or more cross-furrows 3

3. Cross-furrow nearly central Family _Peridinidae_ (cf. _Oxytoxum_)

Cross-furrow close to Family _Dinophysidae_ anterior end

Several cross-furrows Family _Polydinidae_ and flagella (One genus, _Polykrikos_.)

KEY TO MARINE GENERA OF PROROCENTRIDae.

Diagnostic characters: The transverse furrow is absent and the two flagella arise from the anterior end of the body. The sh.e.l.l may be bivalved.

1. No tooth-like process dorsal Genus *_Exuviaella_ to the flagellum

2. With tooth-like process dorsal Genus _Prorocentrum_ to the flagellum

* Presence at Woods Hole indicated by asterisk.

KEY TO MARINE GENERA OF PERIDINIDae.

Diagnostic characters: The cross-furrow is nearly central (see, however, _Oxytoxum_); the body may or may not have a sh.e.l.l; the sh.e.l.l may or may not be composed of distinct plates; the plates are distinguished as _equatorial_ (_i.e._, bordering the cross-furrow), _apical_, and _antapical_, while still another, the ”rhombic plate”, may be present, extending from the cross-furrow to the apex.

1. Without distinct sh.e.l.l Genus *_Gymnodinium_

With a distinct sh.e.l.l 2

2. Sh.e.l.l not composed of definite 3 plates

Sh.e.l.l composed of definite plates 4

3. Cross-furrow replaced by Genus _Ptychodiscus_ thin-skinned band

Cross-furrow well defined; Genus _Protoceratium_ reticulate markings raised on sh.e.l.l-surface

Cross-furrow well defined; Genus *_Glenodinium_ no markings

4. Two parts of sh.e.l.l equal or 5 nearly equal

Two parts of sh.e.l.l very unequal 11

5. With transverse flagellum in 6 a distinct furrow

Transverse flagellum not in a 10 furrow

6. With horns, or with wing-like 7 processes