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. Sh.e.l.ls 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 sh.e.l.l may have a distinct indentation in the anterior edge. There are two lateral, discoid, brown chromatoph.o.r.es, 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 sh.e.l.l is ovate, rounded and swollen posteriorly. The anterior border of both sh.e.l.ls is slightly indented. The sh.e.l.l is quite thick.

The animal moves through the water very slowly. Dark brown in color.

Length 48; width 44.

[Ill.u.s.tration: Fig. 18.--_Exuviaella lima_.]

Exuviaella marina Cienkowsky. Fig. 19.

A smaller form than the preceding, more elliptical in outline, with a thinner sh.e.l.l and with large granules throughout the endoplasm.

The nucleus is spherical and subcentral in position and possesses a distinct central granule. This may be a small variety of _E. lima_.

[Ill.u.s.tration: Fig. 19.--_Exuviaella marina_.]

Genus GYMNODINIUM Stein '78.

(Bergh '81; Kent '81; Pouchet '83, '85; Entz '84; Schutt '95.)

The general structure of these forms is similar to that of _Glenodinium_; the most striking and positive difference is the absence of a sh.e.l.l. The animals are, as a rule, spherical, yet they may be pointed at the two ends or at one of them. They are also frequently flattened dorso-ventrally. The transverse furrow may be either circular and straight around the body or may describe a spiral course, pa.s.sing even twice around the body. The flagella arise near cross-furrow or, in some cases, in longitudinal furrow.

Chromatoph.o.r.es may or may not be present and food-taking is holozoic, in many cases at least. In some cases ectoplasm and endoplasm can be distinguished. Fresh and salt water.

Gymnodinium gracile Bergh '82, var. sphaerica, n. Fig. 20.

The body is divided by the transverse furrow into a shorter anterior and a longer posterior part. The longitudinal furrow is broader at the posterior extremity than at the cross-furrow. The structural feature upon which this new variety is made is the unvarying plumpness of the body, making it almost spherical, except for a slight flattening dorso-ventrally. The nucleus is large and ellipsoidal, with characteristic longitudinal markings of chromatin.

The endoplasm is evenly granular, with a number of large ingested food bodies. The color is brown, not rose-red as in Bergh's species, nor is the Woods Hole form as large as the latter. Length of body 68; width 55. Common.

[Ill.u.s.tration: Fig. 20.--_Gymnodinium gracile_, var. _sphaerica_.]

Genus GLENODINIUM (Ehr.), Stein '83.

(Bergh '82; Butschli '86; Pouchet '85; Daday '86.)

Small globular forms with two distinct furrows, one transverse around the body, the other longitudinal upon the face only. The sh.e.l.l is soft and structureless with a distinct aperture near the meeting point of the two furrows. The endoplasm usually, but not always, contains a bright red eye-spot.

Fresh and salt water.

Glenodinium compressa, n. sp. Fig. 21, a, b, c.

This species resembles _G. ac.u.minata_ of Ehrenberg except that it is strongly compressed laterally. The longitudinal furrow extends nearly to the extremity of the animal. It begins as a narrow slit and widens as it progresses upon the left side; it also becomes much deeper on this side and at the bottom of the depression the longitudinal flagellum is inserted. The transverse furrow runs evenly around the body near the upper pole, giving to the sh.e.l.l almost the aspect of an _Amphidinium_. Brown chromatoph.o.r.es may or may not be arranged radially about a central amylum granule. One striking characteristic is the depth of the two furrows. The nucleus is elongate and somewhat curved; it lies against the posterior wall of the rather thick sh.e.l.l.

Not uncommon.

Length 40; breadth 32; width 18.

The posterior end of the animal is often somewhat pointed and this point frequently becomes attached, so that the animal whirls around upon it as upon a pivot.

[Ill.u.s.tration: Fig. 21 a, b, c.--_Glenodinium compressa_, n. sp.]

Glenodinium cinctum Ehr. Fig. 22.

The body is globular, smooth, and h.o.m.ogeneous. Brown chromatoph.o.r.es arranged radially, each in the form of a cone, the base of which rests against the sh.e.l.l while the points turn inward. A bright-red eye-spot may or may not be present; when present it is placed near the junction of the two furrows. The longitudinal furrow is small.

Fresh water and salt.

Length and diameter the same, 21.

This species was observed by Peck '93.

[Ill.u.s.tration: Fig. 22.--_Glenodinium cinctum_.]

Genus PERIDINIUM Ehr. '32, Stein '83.

(Claparede & Lachmann '58; Bergh '81; Pouchet '83; '85; Gourret '88; Butschli '86.)

The form is globular, ovoid or elongate, the apex frequently drawn out into a long tube. The transverse and longitudinal furrows are quite distinct, the former having often a spiral course about the body. The two halves of the body are similar, the posterior being somewhat shorter; the anterior half has seven equatorial plates, an oral plate, two lateral apical plates, and one or two dorsal plates.

The two antapical plates frequently have a tooth-like process. The bodies are colorless, green or brown.