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HARVARD UNIVERSITY

LIBRARY

OK THE

Museum of Comparative Zoology

S^AY 2 6 1933

V7 i.^Y

/IDemotrs ot tF)e /BJuseum of Comparattvc Zoology

AT HARVARD COLLEGE.
Vol. LIV, No. 1.

REPORTS ON THE SCIENTIFIC RESULTS OF THE EXPEDITION TO THE EAST-
ERN TROPICAL PACIFIC, IN CHARGE OF ALEXANDER AGASSIZ, BY THE
U. S. FISH COMMISSION STEAMER "ALBATROSS," FROM OCTOBER, 1904,
TO MARCH, 1905, LIEUT.-COMMANDER L. M. GARRETT, U. S. N., COM-
MANDING.

XXXVI.

THE DINOFLAGELLATA: THE FAMILY
HETERODINKDAE OF THE PERIDINIOJi>AE.

By CHARLES ATWOOD KOFOID AND AL AST AIR MARTIN ADAMSON.

WITH TWENTY-TWO PLATES.
[Published by permission of Henry O'Malley, U. S. Fish Commissioner]

CAMBRIDGE, U. S. A.

printeD for tbe flDuseum.

1933.

/IDemotrs of tbe /iDuseum ot Comparattve ZooloGt»

AT HARVARD COLLEGE.
Vol. LIV, No. 1.

REPORTS ON THE SCIENTIFIC RESULTS OF THE EXPEDITION TO THE EAST-
ERN TROPICAL PACIFIC, IN CHARGE OF ALEXANDER AGASSIZ, BY THE
U. S. FISH COMMISSION STEAMER " ALBATROSS," FROM OCTOBER, 1904,
TO MARCH, 1905, LIEUT. -COMMANDER L. M. GARRETT, U. S. N., COM-
MANDING.

XXXVI.

THE DINOFLAGELLATA: THE FAMILY
HETERODINHDAE OF THE PERIDINIOH^AE.

By CHARLES ATWOOD KOFOID AND ALASTAIR MARTIN ADAMSON.

WITH TWENTY-TWO PLATES.
[Published by permission of Henry O'Mallev, U. S. Fish Commissioner]

CAMBRIDGE, U. S. A.

printeD tor tbe /Duseum.

1933.

CONTENTS

REPORTS on the scientific results of the Expedition to the Eastern Tropical Pacific, in charge
of Alexander Agassiz, by the U. S. Fish Commission Steamer "Albatross," from
October, 1904, to March, 1905, Lieut. -Commander L. M. Garrett, U.S. N., commanding.
XXXVI. The Dinoflagellata: the family Heterodiniidae of the Peridinioidae. By
Charles Atwood Kofoid and Alastair Martin Adamson. With 22 plates.

CONTENTS

PART I. Introduction and Collections
Acknowledgments .....

PART II. Systematic Account
The family Heterodiniidae
Place of Heterodinium in the Peridinioidae
Heterodiniuni Kofoid ....

Diagnosis .....

Organology ...

Reproduction .....

Occurrence . . ...

Historical discussion ...
Valid species of Heterodiniidae with known
stations ......

Adaptive characters ...
Relationships among the species
Comparisons ....

Key to the subgenera of Heterodinium Kofoid
Subgenus Sphaerodinium Kofoid
Key to the species of the subgenus Sphaerodinium
The kofoidi group . .

Heterodinium doma (Murray & Whitting)
H. calvum Kofoid ....

The minutum group

H. minutum Kofoid & Michener

H. obesum Kofoid ....

H. murrayi Kofoid
H. milneri (Murray & \Vhitting)
H. superbum Kofoid
H. gloliosum Kofoid .
Subgenus Heterodinium nom. subgen. nov.
Key to the species of the subgenus Heterodinium
The expansum group ....

H. expansum Kofoid ....

H. angulatum Kofoid & Michener
H. spiniferuni Kofoid & Michener
H. fenestratum Kofoid
H. praetextum Kofoid
The dispar group ....

H. dispar sp. nov. ....

H. elongatum Kofoid & Michener

H. leiorhynchum (Murray & Whitting)

H. hindmarchii (Murray & Whitting)

Status of H. hindmarchii forma maculatum

H. curvatum Kofoid

H. blackmani (Murray & Whitting)

istnl

ution

Kofoid

and

number of

record

Page

11
II
II
12
12
12
16
16
20

22
24
25
28
29
29
30
30
30
32
34
34
36
38
41
43
45
47
48
48
49
51
52
54
56
58
59
61
64
66
68
70
74

CONTENTS

The rigdenae group

H. rigdenae Kofoid

H. scrippsi Kofoid
Subgenus Platydinium Kofoid
Key to the species of the subgenus Platydinium Kofoid
The pavillardi group

H. agassizi Kofoid

H. fides Kofoid

H. whittingae Kofoid

H. laticinctum Kofoid

H. asymnietricum sp. nov.

H. laeve Kofoid & Miehener
The gesticulatum group

H. mediocre (Kofoid)

H. sinistrum sp. nov.

H. deformatum (Kofoid)

H. gesticulatum (Kofoid)

H. extremum (Kofoid)

H. varicator sp. nov.

H. scotti sp. nov.
Dolichodinium gen. nov.
Diagnosis
Description
Comparisons
Synonymy
Distribution
Reproduction

D. lineatum (Kofoid & Miehener)

PART III. Distribution ok the Heterodiniidae at the Stations of the
Expedition ......

Bibliography
Index

Page

100

102

105

107

109

113

116

118

120

121

122

125
133
135

I. INTRODUCTION AND COLLECTIONS

The family Heterodiniidae comprises a number of relatively rare species of
the Peridinioidae restricted to warm temperate and tropical seas. They are
seemingly a depauperate group occurring mainly in the deeper levels of the il-
luminated zone. This is illustrated by the fact that only 17, or 7.1%, of our 240
station records of species of this family are from surface hauls. It was the cus-
tom on the Expedition to the Eastern Tropical Pacific to make subsurface hauls
with No. 12 and No. 25 silk nets. The nets were lowered with the ship at slow
speed to an estimated depth of 300 fathoms, towed for 20 minutes, and then
brought to the surface with the ship still at slow speed. The catch was thus
taken mainly at 300 fathoms, but intermingled with the plankton from 300-0
fathoms. It was this method of collection which gave the extraordinary repre-
sentation of this family in the collections of this Expedition, as compared with
their seeming paucity in the plankton collected by expeditions using vertical
hauls for the collection of the microplankton.

This monograph includes only the family Heterodiniidae containing the two
genera Heterodinium and Dolichodinium; the former with the three subgenera
Sphaerodinium, Heterodinium, and Platydinium, and thirty-four species, of
which thirty-three are from the collections of the Expedition ; and the latter with
one species only. Of the thirty-five species, five are new, as is also the genus
Dolichodinium. Four of the five are from the plankton of the Expedition, and
the fifth, Heterodinium scotti, was figured in the account of Scott's Antarctic Ex-
pedition, but taken in tropical waters "on the way out."

A full account of the route of the Agassiz Expedition to the Eastern Tropical
Pacific in 1904-1905 will be found in the report of its Director, Alexander Agassiz
(1906), together with maps and lists of collecting stations referred to in this
monograph. A discussion of the methods of collection and examination of the
microplankton will be found in the earlier monograph on the Dinophysoidae
(Kofoid and Skogsberg, 1928). The principles followed in the treatment of the
morphology, comparisons, variation, distribution, and frequency of occurrence,
in this monograph, are essentially similar to those utilized in the monograph on
the Dinophysoidae.

10 INTRODUCTION

Acknowledgments

The authors are under deep obligations to Mrs. Josephine Rigden Michener
for her aid in searching out these rare and elusive organisms, and to her skill in
analyzing and drawing their complicated finer structure. The transfer to Ross-
board was made by Mr. A. B. Streedain. The delicacy of detail and contour in
the finished plates are due to his technical skill. For grants in aid, we are in-
debted to the late Alexander Agassiz, to the Carnegie Institution, through the
late Alfred G. Mayor, and especially to the University of California, which has
continuously aided this enterprise through grants by its Board of Research.

Acknowledgments are made to the Council of the National Academy of
Sciences and to its Committee on Funds for Publication of Research for a grant
in aid of the publication of this Memoir.

II. SYSTEMATIC ACCOUNT

The Family Heterodiniidae Lindemann

Helerodiniaccae Lindemann, 1928, pp. 95, 96, fig. 82.

These are Dinoflagellata of the Tribe Peridinioidae with the postcingular
list reduced or lacking, but in which the anterior list is always present, is usually
well developed, and is often supplemented by an angular projection of the body
wall itself. In addition to the apical pore, which is usually deflected to the right
asymmetrically, there is always present a peculiar, reniform or lobed, bordered pit
or opening, located about midway between the apex and the girdle, to the right
of, or in, the midventral suture of the epitheca. The type genus is Heterodinium
Kofoid (1906a). The distribution of the family is in warm temperate and
tropical seas.

Place of Heterodinium in the Peridinioidae

Lindemann (1928), in his " Pflanzenfamilien " monographic account of the
genera of the Peridineae, established a separate family for the single genus
Heterodinium, the Heterodiniaceae( = Heterodiniidae). He placed it in juxtaposi-
tion to his Ceratiaceae ( = Ceratiidae) and Goniodomaceae ( = Goniodomidae).
The relations of the Heterodiniidae are obviously not very close to any other
family. It is nearest, perhaps, to the Ceratiidae. It is linked to that family by
the four apical plates of Dolichodinium, and its ventral pore is homologous to
that of the subgenus Poroceratium in position, though not in relation to apical
suture. On the other hand, the three apicals link it with the Goniodomidae. In
the general forms of the body, the Heterodiniidae resemble those of the Peridin-
iidae more than those of any other family.

It differs from the Ceratiidae in having 6 precingulars instead of 5, and 6 or 7
postcingulars instead of 5 ; from the Peridiniidae in having 3 antapicals instead of
2 or 1 ; and from the Goniodomidae in having 6 or 7 postcingulars instead of 5.
None of these families has the left anterior intercalary plate, and in none of them
is the postcingular list degenerate.

The family Heterodiniidae contains two genera, Heterodinium Kofoid
(1906a,) with 40 species, and Dohchodinium gen. nov., with 1 species. They
differ in plate formula. Heterodinium has 3 apicals (l'-3'), 1 anterior inter-

12 THE DINOFLAGELLATA

calary (1"), 6 precingulars (l"-6"), 6 (?) girdle plates (1-6), 7 postcingulars
(l"'-7"'), and 3 antapicals (l""-3""). Dolichodinium has the formula 4', 0% 6",
6 (?), 6" ', and 3" ".

Heterodinium Kofoid

Peridiniiim Mdrray & Whittinq, 1899, parlim, p. 326-328; pi. 29, 30, see also Heterodinium; Hensen,
1911, parlim, p. 174, fig. C, see also Heterodinium.; Lindemann, 1928, p. 95-96, fig. 82.

Heterodinium. Kofoid, 1906a, p. 341-368, pi. 17-19; 1907, p. 177 185, pi. 6 8; Kofoid & Michener, 1911,
parlim, p. 284-286, for //. linealum see Dolichodinium: Jorgensen, 1911, p. 148.

Diagnosis: — Body usually slightly asymmetrical, strongly flattened dor-
sovent rally (subgenera Heterodinium and Platydinium), or sphaeroidal (sub-
genus Sphaerodinium), with two large antapical horns or spines (except in some
species of Sphaerodinium); girdle submedian, lacking the post-cingular ridge
entirely or in part ; without lists ; sulcus a short and very nairow groove ; a reni-
form or circular pore present in a characteristic ventral area at the meeting of the
mid- ventral and apical-precingular sutures of the epitheca; plate formula, 3', P,
6", 6, or 7?, 7" ', 3" ", constant; theca hyaline, characteristically reticulated and
porulate, rarely only porulate.

Widely distributed but rare in tropical and subtropical seas, a few only
in warm temperate seas.

The type species is H. scrippsi Kofoid from the California Current off South-
ern California.

Organology: — Within the genus, defined as it is by definite and fixed charac-
ters of the thecal plates, there is a very wide range of modification of the general
form of the body from almost perfectly spherical species like H. sphaeroideum
(Plate 15, fig. 2), to the flattened and highly modified species like H. gesliculalum
(Plate 16, fig. 37), the plate-like body of H. imquale (Plate 16, fig. 32), and the
elongated tapering form of H. hlachmani (Plate 15, fig. 25). The first tj'pifies the
subgenus Sphaerodinium (Plate 15, fig. I-IO) in that the body, though variously
modified, is always circular at the girdle. In all the others there is a dorsoventral
flattening, and, in most of them, a very characteristic flattening or excavation
in the midventral region, almost always to be observed on the hypotheca. In
the subgenus Platydinium (Plate 16, fig. 26-40) the epitheca is similarly modified
to such an extent that it assumes a scoop-like form. Even in most of the spheroi-
dal species the same character is suggested, and there is always some indication
of torsion of the body in a clockwise direction manifested by the distal displace-
ment, and in a few species by the overlap, of the girdle, an asymmetry possibly
connected with the course followed in swimming. The body is almost always

SYSTEMATIC ACCOUNT 13

widest at the girdle, H. agassizi (Plate 16, fig. 27) and several species of the H.
gesticulatum (Plate 16, fig. 34-40) group being exceptions, and divided by it
more or less equally.

The epitheca and hypotheca are thus subequal, and the girdle tends to be
quite oblique, except in Sphaerodinium, with its ventral arcs dipping posteriorly.

The epitheca is usually i-ather less than the transdiameter in altitude, though
exceeding it somewhat in some species, for example, in H. blackmani (Plate 15,
fig. 25). Its apex is contracted into a definite apical horn only in the expansum
group (Plate 15, fig. 11-15). It is usually very broadly and evenly rounded in all
the species of the subgenus Platydinium, except in H. fides, where a deep pre-
cingular constriction sets off an expanded apical region. A differentiated apical
horn, when present, is usually asymmetrical; in H. spiniferum (Plate 15, fig. 13)
it attains a length of only 0.5 transdiametcrs. In H. curvatum and //. blackmani
(Plate 15, fig. 24, 25) it is deflected to the right and the apical pore in Platydinium
is often so deflected.

The hypotheca narrows behind the girdle more than the epitheca, and is
characteristically asymmetrically bifurcated at the antapex into two large stout
horns, somewhat after the manner of most species of Peridinium. However, in
a few species, in fact in all of the subgenus Sphaerodinium (Plate 15, fig. 1-10),
the antapex is rounded, evenly in H. kofoidi, H. sphaeroideum, and H. dorna
(Plate 15, fig. 1-3), asymmetrically in H. calmim (Plate 15, fig. 4). It bears
spines instead of hollow horns in H. 7ninutum, H. obeswm, and H. murrayi (Plate
15, fig. 5-7).

The antapicals are much deflected to the left in H. asymmetricum (Plate 16,
fig. 31) and to the right in H. varicator (Plate 16, fig. 39). The aberrant and
unusual condition of the suppression of one of the antapicals, with compensatory
adjustments elsewhere, occurs in two species. In //. defornialum (Plate 16,
fig 35) it is the right horn thus deficient; in H. sinistrum (Plate 16, fig. 36) it is
the left. A character unique in the Peridinioidae is found in the sinistral lobe of
the H. gesticulaium group (Plate 16, fig. 34-40). This is the lateral extension on
the left margin of the hypotheca at the level of the postcingular-antapical suture,
and is accompanied by a compensatory reduction in volume on the right side of
the hypotheca. Lateral denticles on one or both sides of the suture appear on
the sinistral lobe in H. mediocre (Plate 16, fig. 36). With this sinistral extension
on the hypotheca, there is often a dextial shifting of the apical pore of the
epitheca.

The girdle which encircles the body at its widest part and is usually located

14 THE DINOFLAGELLATA

in the middle equatorial region is remarkable in being almost invariably de-
ficient, wholly or in part, in its postcingular rim. This rim is sometimes de-
veloped only in the proximal part and fades away distally. The precingular rim,
in contrast, is unusually prominent and steeply overhangs the shallow furrow
which, if indented, is deepest anteriorly against the precingular rim. In extreme
cases, for example in H. gesticulatum (Plate 16, fig. 37), the whole girdle is incom-
plete distally. Outstanding fists are never developed in the margins of the
girdle, though the rim may be a much thickened lidge. The girdle is sometimes
perfectly horizontal, without displacement, but more usually it is a descending
right spiral displaced distally by its width only. In only a few species, such as H.
murrayi and H. glohosuvi (Plate 15, fig. 7, 10), is it widely displaced with its
proximal end overlapping the distal. In many highly modified species the
girdle is oblique, tilting ventrally; in H. laticinctum (Plate 16, fig. 30) it is in-
clined at 45° to the horizontal.

The sulcus is invariably a very narrow groove, beginning in a small circular
depression at the proximal end of the girdle, in which lies the flagellai- pore, and
extending with little or no expansion to the end, usually little more tlian half way
to the antapex. The constancy of its form is rather remarkable. Its latera
margins are usually thickened ridges, but spreading fins are never well developed.
The sulcus lies in the deep midventral depression of the hypotheca. It never
extends upon the epitheca.

The theca is definitely divided into plates which, by reason of the fineness of
the suture lines in some cases, and in others of the heavy reticulation of the entire
surface, are not always easily analyzed; but which prove to be constant in number
in all cases of complete analysis, and to vary less in relative sizes than in most
genera with species so diversified as in Heterodinium.

The plate formula is 3', 1% 6", 6 [or 7?], 7" ', 3" ".

At the apex is a small closing platelet, or perhaps more generally, a small
open pore. Around it are three apical plates, l'-3', a large dorsal (2'), and two
ventrals (1' and 3'), separated by the prominent midventral suture attached to
which is the platelet of the ventral area containing the ventral pore. There are
six precingulars; two large ventral plates (1" and 6"), two smaller dorsals (3" and
4"), and two dorsolaterals (1" and 5"). On the left shoulder is the characteristic,
small, anterior intercalary plate (P), usually of nearly the same size as pre-
cingular 2".

The number of girdle plates is uncertain. The sutures separating them are
not clearly defined as in other genera. Their presence is sometimes suggested by

SYSTEMATIC ACCOUNT 15

faint suture ribs and by the distribution of pores, as in H. calvum (Plate 1, fig.
1-3). Seven girdle plates (1-7) were found in H. laticinctum. The unusually
large number of seven postcingulars occurs in this genus. Of these, 1 " ' is small
like the same plate in Gonyaulax and Amphidoma, 4" ' is usually middorsal, and
6" ' is larger than the others, reaching the antapex and forming part of the left
horn in species in which antapical horns are present. In species with antapical
horns, postcingular 7" ' seems to be more or less pushed up into the girdle in con-
tact with the precingular 6". Of the three antapicals, 3" " is large, forming the
doisal side of the antapical region, while 1" " and 2" " are small and pushed to the
right of the downward extension of postcingular 7" '.

At the meeting place of the four suture lines visible on the ventral face of the
epitheca there is developed a characteristic ventral area, sometimes separable as
a platelet, and usually distinguished from the rest of the theca by the absence
of surface markings. It is circular, squarish, or elongated obliquely antero-
posteriorly. It invariably contains a ventral pore which is circular or reniform,
and located somewhere near the middle of the ventral area. The concavity of
the reniform structure is usually directed more or less to the right. The function
of both of these structures is entirely unknown. In H. fenestratum (Plate 7, fig. 5)
a small canal runs from the pore posteriorly to a vacuole in the cytoplasm. This
area is a very distinctive generic character.

The thecal wall is delicate in structure, thin, generally very hyaline, and in
most cases has a very characteristic, beautifully reticulated structure. With few
exceptions it is composed, apparently on both sides, inside and out, of a reticula-
tion of large polygons, sometimes formed of rather fine lines, but usually of
heavier bars which in some species with large reticulations are correspondingly
heavier. It is, however, characteristic of this genus that the theca, because of its
transparency, has a delicacy of structure unusual among armored dinoflagellates.
There is something characteristic of the genus in the pattern of the reticulations.
The polygons are mostly hexagons, not infrequently quadrilateral near suture
lines ; but the reticulations are never quite uniform and the sizes and shapes of the
polygons therefore vary from one part to another. In almost all cases each has a
single minute central pit or pore. Several pits in each polygon occur only in H.
fenestratum (Plate 7, fig. 1). In a few species, for example in H. calvum, the only
surface markings are the somewhat evenly distributed pores. It is possible,
though hardly probable, that the few specimens which have been observed of
these rather exceptional species were all young with the sculpturing incomplete.
In others, notably H. globosum and H. hlackmani (Plate 9, fig. 1-3) and in the

16 THE DINOFLAGELLATA

gesticulatum (Plate 12, fig. 1-5) group, the sculpturing is characteristically irregu-
larly and incompletely developed, being absent on some plates, and only partially
covering others. This may be the result either of the recent formation of the
theca or of resorbtion for hydrostatic adjustment. It is rather a curious phenom-
enon in that it is usually the right side (see H. hlachnani, Plate 9, fig. 1, and Mur-
ray and Whitting, 1899, pi. 29, fig. 6a, b, c) which is deficient. This is the same
region as that in which the girdle also is less developed than in its left or proximal
region. Fine reticulations, apparently secondary, may develop along the suture
lines and on intercalary bands prior to ecdysis. These apparently proceed in de-
velopment from the edges of the coarser primary reticulum into the widening,
smooth intercalary zones.

Few observations have been made on the cell contents of living specimens
belonging to this genus, which is not surprising, for the individuals are rare and do
not often occur in surface collections in neritic plankton. The plasma is hyaline
and colorless, vacuolated, and does not often completely fill the theca. The
nucleus is of the usual dinoflagellate type, but often small and difficult to ob-
serve. Chromatophores are sometimes absent, and when present, their size is
always small and number few. They are usually pale green or greenish yellow,
irregularly spheroidal, and distributed at the periphery, or often aggregated into
spheroidal, centrally located chromospheres. It is impossible with the few data
at hand to say anything more definite about the cell contents of the living or-
ganisms and nothing whatever is known about their movements, reproduction,
and other activities.

The absence of, or small number of, chromatophores, and the extreme
hyalinity of the whole organism may be correlated with its habitat in the lower
levels of the fight zone of the sea.

Reproduction: — Nothing is known of fission or encystment in this genus.
The development of intercalary zones, as in H. praetextuvi (Plate 7, fig. 3), H.
hlackmani (Plate 9, fig. I), H. curvatum (Plate 9, fig. 5, 6), and H. doma (Plate 1,
fig. 1-3), is suggestive of asexual reproduction by binary or multiple fission after
ecdysis, as in Peridinium, rather than by binary fission accompanied by skeletal
fission, as in Ceratium. The occurrence of intercalary zones, though rare in our
material, renders this hypothesis quite probable and its probability is increased
by the purely negative evidence of the entire absence of any trace whatsoever of
a fission line in all specimens thus far examined.

Occurrence: — The occurrence (Plates 13, 14, and 17, fig. 41) of the many and
varied members of this large genus is very remarkable in that all of them, without

SYSTEMATIC ACCOUNT 17

exception, are relatively extremely rare and very meagerly represented, as far as
is known, in all seas, except those explored by this Expedition. Indeed, of the
thirty-nine species, only twelve have been found outside the Pacific. All but
seven of the known species, namely, Heterodinium crassipes, H. inaequale, H.
kofoidi, H. pavillardi, H. scotti, H. sphaeroideum, and H. trirostre, are present in
our collections. This seeming limitation is, however, probably only a function of
the degree of exploration rather than a regional predilection or limitation.

The genus is represented (Plates 13, 14, Plate 17, fig. 41) at sLxty-one (48%)
of the 127 stations (Plates 13, 14), with 10, 12, 12, 13, 12, and 2 stations on the six
hues of the Expedition. These are distributed over the following regions: two
(4580, 4583) are in the California Current; seven (4587, 4590, 4594, 4596, 4604,
4605, 4609) in the Mexican Current; four (4613, 4634, 4637, 4638) in the Panamic
Area; ten (4647, 4648, 4650, 4657, 4659, 4664, 4667, 4669, 4670, 4676) in the Peru-
vian Current; twenty-seven (4679, 4680, 4681, 4683, 4685, 4686, 4687, 4688,
4701, 4705, 4706, 4707, 4709, 4711, 4717, 4719, 4721, 4722, 4724, 4728, 4730,
4732, 4734, 4736, 4737, 4739, 4740) in the South Equatorial Drift; eight (4689,
4691, 4692, 4695, 4697, 4698, 4699, 4700) in the Easter Island Eddy; two (4713,
4715) in the Galapagos Eddy; and one (4742) in the South Equatorial Current.

The great majority (223 of 247) of the station records, including those at
Station 4580 two species, 4583 three species, 4587 one species, 4590 one species,
4594 three species, 4605 one species, 4609 one species, 4613 one species, 4634 two
species, 4637 five species, 4638 four species, 4648 one species, 4650 two species,
4657 one species, 4659 two species, 4664 one species, 4667 one species, 4676 three
species, 4679 eight species, 4681 four species, 4683 four species, 4685 two species,
4687 three species, 4689 three species, 4691 sixteen species, 4695 nine species,
4697 thirteen species, 4699 sixteen species, 4701 nineteen species, 4705 seven
species, 4707 four species, 4709 three species, 4711 two species, 4713 two species,
4715 four species, 4717 two species, 4719 one species, 4721 two species, 4722 four
species, 4724 eleven species, 4728 one species, 4730 five species, 4732 ten species,
4734 eight species, 4736 three species, 4737 five species, 4739 seven species, 4740
four species, 4742 four species, were in hauls from 300-0 fathoms; only seventeen
records, viz.: — at Stations 4583 two species, 4590 two species, 4596 one species,
4604 one species, 4669 one species, 4680 two species, 4686 one species, 4688 one
species, 4692 three species, 4698 one species, 4700 one species, 4706 one species,
are from surface hauls, or at 21% of the total number of stations at which dino-
flagellates were taken at the surface. At Station 4737 the genus was repre-
sented by three species from 100-0 fathoms, and atone station (4587) one species

18 THE DINOFLAGELLATA

was recorded at this depth. At seven stations, inchiding records at Stations
4647 one species, 4670 two species, 4681 five species, 4689 four species, 4701 three
species, 4724 three species, 4732 two species, it was taken in catches made by
vertical hauls from 800-0 fathoms.

The range in surface temperatures at the 61 stations was from 66° F. in the
Peruvian Current to 85° F. in the Mexican, and the average over all was 75.6° F.

The frequency for each species was almost always less than 1%. The
records of frequency exceeding that amount are as follows: 3% H. curvalum
(4692); 2% H. curvatum (4698); 1% H. agassizi (4657), H. blackmani (4707,
4739), H. curvatum (4739), H. mediocre (4715, 4742), H. gesticulatum (4689 two
hauls, 4697), H. globosum (4691, 4692), H. dispar (4683, 4685, 4692, 4695, 4701),
H. viilneri (4676, 4724), H. obesum (4681), H. rigdenae (4695, 4732, 4737, 4742),
H. scrippsi (4580), and H. whillingae (4691, 4715). In the remaining 236 station
records of the various species, the frequency is less than 1%; that is, the speci-
mens were found only after 100 other dinoflagellates had been met with in the
course of the search by means of the mechanical stage of microscopical prepara-
tions of the plankton catch in formalin.

The data summarized above show, first, that the horizontal distribution of
the genus Heterodinium in the Eastern Tropical Pacific is of the same general
type as that of most other tropical genera, with the records few and scattered to
the north, but reaching a very marked maximum to the north of Easter Island
and where the route of the "Albatross" again crossed the South Equatorial
Drift to the west towards Manga Reva and the Paumotu Archipelago. The
rarity of the genus in the Peruvian Current is rather more decided than in the
case of most other genera, there being records at only ten stations (4647, 4648,
4650, 4657, 4659, 4664, 4667, 4669, 4670, 4676) in the sixty stations in that cur-
rent. Probably connected with this is its comparative scarcity in the Gala-
pagos Eddy, part of the waters of which take their origin from the Peruvian Cur-
rent. The predominance of occurrences and of speciation in the warmest regions
of the tropics is quite marked in this genus.

The data regarding the vertical distribution in the case of most of the in-
dividual species is too meager for the drawing of detailed conclusions, but in most
of the species, and for the genus as a whole, they show quite clearly that the
optimum depth is not near the surface but somewhere in the deeper levels of the
light zone. Kofoid (1906) states that, off the California coast near San Diego,
no individuals were taken at the surface in many hauls over a period of several
years, but only in vertical catches from between 165 and 40 fathoms to the sur-

SYSTEMATIC ACCOUNT 19

face. He states that the absence of chromatophores, or their aggregation into
chromospheres, is suggestive of occurrence in deep water with diminished hght,
as is also the extreme hyahnity of many of the species. It is perhaps because of
their scarcity at the surface that so few species have been recorded from other
tropical seas in other investigations. Collections on many of the earlier expedi-
tions were made only at or near the surface ; or with nets of coarser mesh, which
permitted the escape of these relatively small organisms through the silk ; or by
vertical rather than intermediate hauls, such as were made on this expedition.

Evidence in the records of the Expedition is insufficient to demonstrate the
restriction of any of the species to particular regions, or of any very significant
differences in distribution, except in numbers, between one species and another.
The restrictions of significance are of a more general type, such as the absence
from the Peruvian Current.

The data with regard to coincident distribution are as follows: there were 19
species taken in the same haul at 1 station, 16 at 2, 13 at 1, 11 at 1, 10 at 1, 9 at 1,
8 at 2, 7 at 2, 5 at 4, 4 at 9, 3 at 11, 2 at 14, and 1 at 20. In the Eastern Tropical
Pacific, the least rare of the species are H. rigdenae (23 records), H. milneri (19
records), H. curvatum (17 records), H. gesticulatum (16 records), and H. globosum
(14 records). Seven are extremely rare, occurring only once: H. angulatum
(4691), H. leiorhynchum (4697), H. praetextum (4740), H. spiniferum (4695),
H. sinistrum (4638), and H. superbum (4699); or twice: H. deformatum (4724,
4736) in our records, and nowhere else with the exception of H. leiorhynchum,
recorded twice by Murray and Whitting (1899) in the Tropical Atlantic.

The genus is seemingly even more rare in other seas, in number of species
as well as in individuals, except for Hensen's (1911) computed numbers, and
Schiller's (1916) reports of the abundance of H. kofoidi in surface waters of the
Adriatic. Most of the few records are from tropical seas; from the Atlantic be-
tween 20° N. and 20° S., a total of eleven (excluding duplicates) species has been
recorded, seven by Murray and Whitting (1899), four by Hensen (1911), and one
by Karsten (1906). In the Indian Ocean, Karsten (1906) recorded but three
species. From warm temperate seas, the only records are from the Mediter-
ranean, H. inequale and H. paviUardi (as kofoidi) from the Gulf of Lyons (Pavil-
lard, 1916), H. kofoidi and H. crassipes from the Adriatic (Schiller, 1916), and
H. leiorhynchum from Naples (Entz, 1907, 1909). In the Pacific, in addition to
the records here given, are those of Kofoid (1906), who found five species in the
summer plankton off San Diego, California. One of these, H. sphaeroideum, has
not been found elsewhere.

20 THE DINOFLAGELLATA

These records from other seas are too few to allow of a comparison with
regard to the relative abundance of different species, between the Pacific and
other oceans. But it may be noted that the majority of the most abundant
species in our collections are among the widely distributed species elsewhere.
For example, H. gesticulatum, one of the commonest in the Pacific, occurs also
in the Atlantic, and H. rigdenae in both the Indian Ocean and Mediterranean.
The relatively greater scarcity of species of this genus in other seas is doubtless
in part only a function of the small number of collections made with fine siUc
nets from deeper waters, and of less complete searching of the catch of plankton.

To sum up, the numerous species of Heterodinium are eupelagic without
exception; they are extremely rare; many appear to be stenobathmic in lower
levels of the light zone; a few have been found to be very widely distributed, but
probably aU are essentially species of tropical and subtropical seas. As far as
Umited data go, their habitat is at least a fair distance below the surface, except
for H. kofoidi, which was found by Schiller (1916) in abundance near the surface
in the Adriatic.

Historical discussion: — The first species of Heterodmium to be figured is
the one which we describe as H. scotii, presumably from the Tropical Atlantic,
which Wilson (1905) sketched among the "Peridineans taken on the voyage
out" of the "Discovery," on Capt. Scott's Expedition to the Antarctic. The
genus was estabUshed by Kofoid (1906a) with thirteen species including H. black-
mani, H. doma, H. hindmarchii, H. trirostre, H. leiorhynchum, and H. viilneri,
previously described by Murray and Whitting (1899) as species of Peridinium
from the Tropical Atlantic, and also their P. tripos to which the new name H.
murrayi was given. Five new species from the plankton of deeper waters of
southern origin off San Diego, namely H. sphaeroideum, H. rigdenae, H. scrippsi,
H. whiltingae, and H. inaequale were added, H. scrippsi being designated as the
type of the new genus. H. triacantha, founded on Gonyaulax triacantha Jorgen-
sen (1899), and also on Ceratium hyperhoreum Cleve (1900), was incorrectly re-
moved to Heterodinium from Gonyaulax where it properly belongs, by Kofoid
(1906), who later (1911) restored it to Gonyaulax. Since then, nineteen more
species and five forms have been described from the collections of this Expedition.
In 1907a Kofoid described and figured as new H. agassizi, H. calvum, H. curva-
tum, H. expansum, H. fenestratum, H. fides, H. gesticulatum (with forma typica,
deformata, extrema, and mediocris), H. globosum, forma maculata (of hindrnarchi
(Murray and Whitting) Kofoid), H. laticinctum, H. longum, H. obcsum, H. prae-
lextum, and H. superhum. In 1911 Kofoid and Michener added descriptions, but

SYSTEMATIC ACCOUNT 21

no figures, of H. angulafum, H. elongatwn, H. laeve, H. lineatum, H. viinutum, and
H. spiniferum.

The division into three subgenera, Euheterodinium (=Heterodinium),
Sphaerodinium, and Platydinium, by Kofoid (1906) for the species then known,
has proved to be suitable for the larger number now known and is adopted
here.

In accordance with the Rules of Nomenclature (Blanchard, 1905) the name
of the subgenus Euheterodinium proposed by Kofoid (January 6, 1906) must be
abandoned and the subgeneric name Heterodinium utilized for the typical sec-
tion of the genus in lieu of Euheterodinium. Owing to the differences in the
plate formula and to the occurrence of fission of the theca in the species described
by Kofoid (1911) as Heterodinium lineatum, we have removed this species from
Heterodinium and established for it a new genus Dohchodinium (p. 00). In
shape of theca, type of porulation, occurrence of fission, and plate formula, this
species is difficult to allocate in Heterodinium which it resembles in girdle, sulcus,
and plate 2' which looks much like the intercalary plate 1* pushed anteriorly so
as to crowd a narrow extension to the apex.

Both references to, and additions to, the genus Heterodinium by other in-
vestigators are few in the literature subsequent to its establishment in 1906.
Jorgensen (1911) cites its occurrence in plankton from the margin of the Gulf
Stream at the Tortugas Station but did not designate the species observed.
Hensen (1911, p. 174, fig. C) names some very crude and often inverted sketches
of a miscellaneous array of species of various genera, all as species of Peridinium.
Included in this incoherent jumble are several which recognizably belong in
Heterodinium, namely his Peridinium venter (his fig. C, 7) which is H. agassizi, as
he conjectures; his P. pulchrum (his fig. C, 8) which is H. curvatuvi; his P. tristy-
luni which is H. gesticulatum, as he conjectures; and his P. dentaturn (his fig. C, 16)
which is H. laticijictum, or close to it. In 1916 (Jan. 8) Schiller described two
new species from the Adriatic, H. crassipes (as H. orassipes in the description of
his figure 1) and H. kofoidi, the smallest (20 ju) known species of the genus.
Shortly afterwards, March 17, 1916, Pavillard (his pi. 2, figs. 1, 2) described from
the Gulf of Lyon a species which he designated also as H. Kofoidi. Since Schiller
had previously utiUzed this specific name a new name is necessary. Pavillard's
species is accordingly here designated as H. pavillardi. In this same paper
Schiller (1916, footnote, p. 209) quotes as Heterodinium tripos the species described
by Murray and Whitting (1899) and later cited by Ostenfeld and Paulsen (1904)
as Peridinium tripos. But this specific name is preoccupied in Peridinium,

22 THE DINOFLAGELLATA

thereby becomes a synonym, and the new name murrayi was assigned to it in
Heterodinium by Kofoid (1906), as shown in the discussion of that species.

The nomenclatural changes introduced or utiHzed in this monograph are the
return of Heterodinium triacantha (Jorgensen, 1899b) Kofoid to Gonyaulax (see
Kofoid, 1911b); the renaming of Peridiniuvi tripos Murray and Whitting (1899)
as H. murrayi (see Kofoid, 1906a); the reduction of Hensen's (1911) Peridinium
dentatum to a synonym of H. laticinctum, his P. pulchrum to H. blackmani, his
P. tristylum to H. gesticulatum, and his P. venter to H. agassizi; the renaming of
Pavillard's (1916) H. Kofoidi as H. pavillardi; and the reduction of H. longum
Kofoid (1907a) to a synonym of H. rigdenae Kofoid (1906a) because the former is
apparently only a form of the latter with wide intercalary bands.

In this monograph the following new species have been described : Heterodin-
ium dispar, H. asymmetricwn , H. varicator, and H. sinistrum. In addition H.
kofoidi Pavillard (1916), preoccupied by H. kofoidi Schiller (1916), is renamed
H. pavillardi, and H. gesticulatum forma mediocris, forma extrcma, and forma
defonnata are raised to specific rank as H. mediocre, H. extremum, and H. de-
formatum. H. scotti is described from Wilson's (1905) unnamed figure.

A few scattered records of occurrences by Karsten (1906, 1907), Entz, Jr.
(1907, 1909), and Pavillard (1915, 1916) constitute the remaining references in
literature to the species of this interesting, but relatively very rare, genus.

The number of valid species in the genus Heterodinium, recognized in this
monograph, is forty. Six of these, namely, Heterodinium crassipes Schiller
(1916) and H. kofoidi Schiller (1916) from the Adriatic, H. inaequale Kofoid
(1906a) and H. sphaeroideum Kofoid (1906a) from the California Current, H.
pavillardi Kofoid (nom. sp. nov.) from the Gulf of Lyon, and H. trirostre (Murray
and Whitting, 1899) Kofoid (1906a) from the Tropical Atlantic, were not found
in the collections of this Expedition, leaving thirty-four here reported for the
Tropical Pacific. In the following hst of the forty species recognized by us as
valid, the author and date for each is given, and the oceanic regions from which
they have thus far been reported is also stated.

Valid Species of Heterodiniidae, with known Distribution
AND Number of Record Stations

Genus Heterodinium.

H. n<7ossiZJ Kofoid (1907a). Tropical Atlantic (49) and Pacific (7).
H. angulalum Kofoid & Michbner (1911). Tropical Pacific (1).
H. asymmciricum sp. nov. Tropical Pacific (4).

SYSTEMATIC ACCOUNT 23

H. hlnckinnni (Murray & Whitting, 1899) Kofoid (1906a). Tropical Atlantic (11), Indian (5), and

Pacific (11).
H. calrum Kofoid (1907a). Tropical Pacific (8).
H. crassipcs Schiller (1916). Adriatic (1).

H. curvaium Kofoid (1907a). Tropical .\tlantic (20) and Pacific (17).
H. deformaium (Kofoid) (1907a). Tropical Pacific (2).
H. dispar sp. nov. Tropical Pacific (13).

H. doma (Murray & Whitting, 1899) Kofoid (1906a). Tropical Atlantic (1) and Pacific (5).
H. elongatum Kofoid & Michener (1911). Tropical Pacific (7).
H. expansum Kofoid (1907a). Tropical Pacific (3).
H. exlremum (Kofoid) (1907a). Tropical Pacific (6).
H.fenestralum Kofoid (1907a). Tropical Pacific (15).
H. fides Kofoid (1907a). Tropical Pacific (5).

H. gesticulatum Kofoid (1907a). Tropical Atlantic (16) and Pacific (16).
H. globosum Kofoid (1907a). Tropical Pacific (14).

H. hindmarchii (Murray & Whitting, 1899) Kofoid (1906a). Tropical Atlantic (12) and Pacific (10).
H. inaequale Kofoid (1906a). California Current (1).
H. kofoidi Schiller (1916). Adriatic (1).
H. laeue Kofoid & Michener (1911). Tropical Pacific (9).
H. lalicinctum Kofoid (1907a). Tropical Atlantic (11) and Pacific (5).
H. leiorhynchum (Murray & Whitting, 1899) Kofold (1906a). Tropical Atlantic (2), Pacific (1), and

Mediterranean (1).
H. mediocre (Kofoid) (1907a). Tropical Pacific (7).

H. milneri. (Murray & Whitting, 1899) Kofoid (1906a). Tropical Atlantic (11) and Pacific (19).
H. minutum Kofoid & Michener (1911). Tropical Atlantic (3).
H. murrnyi (Murray & Whitting, 1899 as Perulinium tripos) Kofoid (1906a). Tropical Atlantic (4)

and Pacific (6).
H. obesuin Kofoid (1907a). Tropical Pacific (6).

H. parillardi nom. sp. nov. Pavillard (1916) as H. kofoidi. Gulf of Lyons (1).
H. praeleitum Kofoid (1907a). Tropical Pacific (1).

H. rigdenae Kofoid (1906a). California Current (1), Tropical Indian (1) and Pacific (23).
H. scotii sp. nov. Wilson (1905, as "Peridinean"). Tropical Atlantic (1?).

H. scrippsi Kofoid (1906a). California Current (1), Tropical Atlantic (2), Indian (1), and Pacific (10).
H. sinistrum sp. nov. Tropical Pacific (1).
H. sphaeroideum Kofoid (1906a). California Current (1).
H. spiniferum Kofoid & Michener (19111. Tropical Pacific (1).
H. superbum Kofoid (1907a). Tropical Pacific (1).

H. trirostre (Murray & Whitting, 1899) Kofoid (1906a). Tropical Atlantic (1).
H. raricalor sp. nov. Tropical Pacific (5).

H. whiUingae Kofoid (1906a). California Current (1) and Tropical Pacific (11).
Dolichodinium lineatum (Kofoid & Michener) (1911). Tropical Pacific (2).

Species from other genera have been inckided in Heterodinium either as
valid species or as synonyms. These, with their authors, dates, and status in
this monograph, are distributed below in their other genera as follows.

Ceratium hyperboreum Cleve (1900c) =Goii;/»h/(7j- Irincantha Jorgensen (\S^%h) =Hclerodi)num tri-

acanlha (Joroen.sen) Kofoid (1906a).
Gonyaidax triacantha Jorgensen (lS99h) = HelrrodiniHm Iriacanlha (Jorgensen) Kofoid (1906a) =

Gornjaulax triacantha Jorgensen, Kofoid (1911b).
Peridiniutn areolaium Karsten (1906, p. ISO, pi. 23, fig. 18a, h) = Heterodinium scrippsi Kofoid

(1906a).
P. blackmani Murray & Whitting (1899) =H. blnckmani (Murray & Whitting) Kofoid (1906a).
P. dentatiim Hensen (1911)=//. laticinctum Kofoid (1907a).

P. doma Murray & Whitting (1899)=//. damn (Murray & Whitting) Kofoid (1906a).
P. hindmarchii Murray & Whitting (1899)=//. hindmarchii (Murray & Whitting) Kofoid (1906a).
P. leiorhynchum Murray & Whitting (1899) = //. leiorhyrwhum (Murray & Whitting) Kofoid

(1906a).

24 THE DINOFLAGELLATA

P. milneri Murray & Whittino (1899)=//. milneri (Murray & Whitting) Kofoid (1906a).

P. pnlchrwn Hensen (1911)=//. cnrmtum Kofoid (1907:i).

P. tripos Murray & Whitting (1899) non Ehrenberg (1834)=-=//. murrayi Kofoid (1906a).

P. trirostre Murray & Whitting (1899) = //. Irirostre (Murray & Whitting) Kofoid (190(Ja).

P. Iristj/lum Hensen (1911)=//. geslicidatum Kofoid (1907a).

P. renter Hensen (1911)=//. a^issizi Kofoid (1907a).

The following specific or other names have been used in the literatui'e of the
genus Heterodinium though the species in question may not have been assigned
by its author to Heterodinium. These names have been discarded in this mono-
graph for the reasons indicated. In so far as we can ascertain, none of them has
been disposed of in any prior publication.

dentntiiin (Hensen, 1911, in Peridinium) =//. laticinctum Kofoid.

longum (Kofoid, 1907a, in Heterodinium) = synonym of //. rigrletme Kofoid.

nrassipes (Schiller, 1916, in Heterodinium) =faps?(s for crassipes.

pvlchrum (Hensen, 1911, in Heterodinium) =//. curvatum Kofoid.

rigdunae (Karsten, 1907, p. 473, in Heterodinium) =/o7)sms for rigdenae.

typica (Kofoid, 1907a, in Heterodinium a,9 forma of H. geslicidatum) =//. gcsticidatnin (Kofoid).

Synonyms were created by Karsten (1906) who published Peridinium areola-
lum, though at the same time stating its identity with H. scrippsi, and by Hensen
(1911), when he published his Peridinium tristylum and P. venter and at the same
time stated that they were probably identical with Heterodinium gesticulatu7n
Kofoid and H. agassizi, respectively. Murray and "Whitting also erred in using
Peridinium tripos for a species when Ehrenberg (1834) had previously applied
the same name in the same genus to a dinoflagellate now known as Ceratium
tripos. Murray and Whitting's P. tripos is renamed Heterodinium murrayi by
Kofoid (1906a). Pavillard (1916) described H. Kofoidi from the Gulf of Lyons,
not knowing that Schiller (1915) had shortly before used the same name for a
different species. On page 86 we designate in this monograph Pavillard's species
as H. pavillardi.

Two names introduced into Heterodinium have been referred to other
genera. Kofoid, in his original account (1906a) of the genus, included Jorgen-
sen's (1899b) Gonyaulax triacantha, which Cleve (1900c) later described as
Ceratium hyperboreum, in Heterodinium. In his later revision of the genus
Gonyaulax, Kofoid (1911b) returned the species triacantha to Gonyaulax. In
this monograph the species Heterodinium lineatum described by Kofoid and
Michener (1911) is made the type species of a new genus, Dolichodinium.

Adaptive characters: — The more primitive species such as the H. kofoidi
group retain the small size along witli the spherical form, and thus maintain a
high specific surface for flotation and do not develop the horns or marked
reticulations. In the larger species such as the terminal members of the ortho-

SYSTEMATIC ACCOUNT 25

genetic series (Plates 15, 16, fig. 1-39) the loss of specific surface due to the
larger size is compensated for by the outgrowth of the apical and antapical horns,
by the flattening of the expanded epitheca as in Platydinium, and by the de-
velopment of rugose reticulations. There is also a considerable development of
vacuoles in the cytoplasm of some of the larger species, such as H. laeve, (Plate 16,
fig. 32) in the absence of surface rugosities. The larger species and the more
highly specialized ones show a tendency towards asymmetry by curvature of the
apical and antapical horns and by the scoop-shaped depression of the epitheca.
These various modifications are devices to assist in flotation by increase of specific
surface (horns and reticulations), by reduction of overweight (hydrostatic
vacuoles), and by producing a wavering motion in sinking (curvature of out-
growths).

The characters of greatest systematic significance within the genus are the
shape of the body, especially of the epitheca and apical horn, the length, shape
and curvature of the antapicals, the structure of the girdle, the surface reticula-
tions, the shape of plates 1^ and 7" ', and the outline of the postmargin.

Relationships among the species: — In the speciation within the genus
Heterodinium a wide range of diversity in form has occurred with at the same
time a retention of the more fundamental generic characters, so constant that its
members form a very well-defined and natural generic group. These characters
are the plate formula and arrangement, especially the presence of I'', the anterior
intercalary, the suppression of the postcingular ridge, the short sulcus, the ven-
tral area on the epitheca with the included ventral pore, and the reticulate struc-
ture of the thecal wall, all of which features, except the last, are clearly expressed
in all of the species. As a result, a subdivision of this genus into subgenera must
deal mainly with form and proportions, must utiUze characters which tend to
intergrade, and must be of sUght value except for convenience in treating so
large a group.

The three subdivisions, proposed by Kofoid (1906a), are here recognized
and the species are divided among these in the keys. They are, however, of un-
equal value, only one of them, the subgenus Platydinium, being a sharply set-off,
natural group, its members being united by having a characteristically scoop-
shaped epitheca, with the apex broadly rounded in ventral view, and by the
agreement in other less striking characters such as antapical horns, asymmetry
of midventral epithecal suture, and prominent ventral pore. This is probably
the most specialized group, all its members being highly modified from the
typical Peridinium-hke form of body. The other two subgenera are also sepa-

26 THE DINOFLAGELLATA

rated on the basis of the form of the body, Sphaerodinium containing the rotund
forms with circular cross-section, and Heterodinium those with more flattened
form and tapering epitheca. Since these characters tend to intergrade among
the species, their separation into the two subgenera is artificial, more or less arbi-
trary in some cases, and is made mainly for convenience in bringing out relation-
ships.

In (Plate 15, fig. 1-25, Plate 16, fig. 26-40) outline sketches of all the known
species have been arranged in the main according to increasing size and growing
complexity of structure. All of the figures have been drawn to the same mag-
nification. The groups conform to the three subgenera: (Plate 15, fig. 1-10)
belong to Sphaerodinium, (Plate 15, fig. 11-25) represent Heterodinium, and
(Plate 16, fig. 26-40) Platydinium. Within the genus as a whole the species can
be seriated in several sequences of orthogenetic type, each beginning with smaller
and simpler species and culminating in ones of larger size, with more complex
surface structure, and more extension of apical or antapical horns, or of both.

We recognize seven such series: in the subgenus Sphaerodinium, the kofoidi
and the minutum groups; in the subgenus Heterodinium, the cxpansum, leiorhyn-
chum, and rigdenae groups, and in the subgenus Platydinium, the pavillardi and
the gesticulatum groups.

The subgenus Sphaerodinium is characterized by the spheroidal form of
the body and no antapicals, or only small ones.

Within Sphaerodinium two orthogenetic series occur. The first, the kofoidi
group (Plate 15, fig. 1-4), contains but four species and is the most primitive one
in the genus, starting with the minute sphaeroidal H. kofoidi (20 n) (Plate 16,
fig. 1) and including H. sphaeroideum, H. doma, and H. calvum (75 m) (Plate 15,
fig. 2-4), all of sphaeroidal shape. No apical or antapical spines or horns occur
in this primitive series, though the highest representative, H. calvum, has an
angular postmargin.

The second series, the minulum group (Plate 15, fig. 5-10), is characterized
by the presence of antapical spines or horns upon a spherical or spheroidal type
of body with an apical horn also emerging in the species above the lowest repre-
sentative. It includes six species, beginning with the small (40 y) spheroidal H.
minutum with minute solid spinules and no trace of an apical horn, and including
H. obesum, H. murrayi, H. milneri, H. superbum, and terminating in the large
H. globosum (117 m) with stout hollow antapicals and well developed apical horn.

The subgenus Heterodinium (Plate 15, fig. 11-25) is characterized by the
tapering conical epitheca and well developed antapicals. Three series of species

SYSTEMATIC ACCOUNT 27

occur in this subgenus; the expansum group (Plate 15, fig. 11-15) with rotund
body and emergent apical horn; the dispar series (Plate 15, fig. 16-21) with elon-
gated body and tapering but not constricted epitheca; and the rigdenae group
(Plate 15, fig. 22-25) with stout flattened epitheca with straight or rotund sides
and no apical horn.

The expansum group (Plate 15, fig. 11-15) contains five species, beginning
with the medium-sized (105 *<) H. expansum with very rotund body and minute
apical and antapicals, including H. angulatum, H. spiniferum, H. fenesirahim,
and terminating in the very large (240 u), heavily reticulated, and much elon-
gated H. praetexhmi, the largest species of the genus. This series represents the
highest degree of Peridinium-like differentiation developed in the genus Hetero-
dinium.

The dispar group (Plate 15, fig. 20-25) contains six species, beginning with
the small (72 m) H. dispar with short epitheca, weakly developed antapicals, and
slight reticulations; it includes in the ascending scale of differentiation H. elonga-
tum, H.leiorhynchum, H. hindmarchii, and H. curvatum; and terminates with the
large (240 m) H. hlackmani, all Peridinium-like in form and proportions. In this
series occur some of the most elaborate developments of surface markings and
suture difTerentiations in the whole genus.

The rigdenae group (Plate 15, fig. 16-19) within the subgenus Heterodinium
leads off in the direction of the subgenus Platydinium. In this group the epitheca
develops from the conical to the inflated type with convex sides in ventral view.
It begins with H. rigdenae, with a low epitheca, subconical in lateral view, and
includes H. crassipes and H. scrippsi, terminating in H. irirostre with straight
lateral margins and spreading antapical horns. In this latter respect it leads off
towards the subgenus Platydinium. The accessory left antapical horn is found
also in H. milneri of the minutum group.

The subgenus Platydinium (Plate 16, fig. 26-40) has a very much flattened
epitheca with convex sides and broadly rounded or expanded apex. It falls into
two groups, the paviUardi group without sinistral lobe and the gesticulatum
group with the lobe. The paviUardi group (Plate 16, fig. 26-33) begins with the
small (90 m) H. paviUardi with low rounded epitheca and short asymmetrical
antapicals and continues through H. asymmetricum, H. inaequale, and H. laeve.
The last species is rather close to H. mediocre, the initial member of the gesticula-
tum group. A side line of species of increasing size, but with widely expanded,
broadly rounded epitheca, and short, more closely approximated antapicals,
includes H. agassizi, H. whittingae, and H. laticinctum. The tendency towards

28 THE DINOFLAGELLATA

lateral constriction of the epitheca, slightly evolved in H. agassizi, reaches a
maximum in H. fides.

The most unique, grotesque, and most asymmetrical group is the H. gesticu-
laium series (Plate 16, fig. 34-40) of six species, characterized by the asymmetrical
hypotheca with projecting sinistral lobe and broadly rounded epitheca. The
series begins with H. mediocre (Plate 16, fig. 36) with only a slight sinistral lobe.
There does not appear to be in the paviUardi series (Plate 16, fig. 26-33) of the sub-
genus Platydinium any indication of this lobe. The nearest approach to it else-
where is seen in the rather divergent H. scrippsi (Plate 15, fig. 18) of the rigdenae
series in the subgenus Heterodinium. H. scrippsi has an angular projection at
the suture where the lobe develops in the gesticulatum series (Plate 16, fig. 34-40),
and fuller shoulders on the epitheca than in any species in the subgenus Hetero-
dinium. The postmargin of H. scrippsi is also asyrmnetrical and broadly angled
as in H. mediocre. The two series in Platydinium are thus rather independent,
except for the similarity in the epitheca.

The gesticulatum group (Plate 16, fig. 34-40) includes H. ryiediocre, H. vari-
cator, H. extremum, H. gesticulatum, H. scotti, H. deformatum, and H. sinisirxim.
The first four form a series of increasing emergence of the sinistral lobe, and the
last two are divergent, perhaps degenerate, types in which the right and left
antapicals, respectively, are suppressed in development with compensatory ad-
justments in the shape of the epitheca and the shifting of the surviving antapical
towards the median fine.

Certain general tendencies appear in all of the seriated groups, as they have
been arranged, as follows: (1) towards increase in volume; (2) towards increase in
length; (3) towards development of apical and antapical horns; (4) towards in-
creasing curvature of the horns; and (5) towards development of reticulations.
Each series progresses from a small spherical, or more or less rotund tjT^e with
less development of outgrowths and, in most cases, less reticulation, towards
those with peripheral enlargements and differentiations.

Comparisons: — A near relationship of Heterodinium to Peridinium is
suggested by the superficial resemblance of its species to those of that genus,
especially of many species of the subgenus Heterodinium which have the same
deep bifurcation into two antapical horns and tapering epitheca, for example in
H. blackmani, as is found in P. grande. On this basis it would appear that
Heterodinium is more nearly aUied to Peridinium than to any other genus; but
the thecal plates, especially on the epitheca, are of an entirely different type.
Peridinium has its intercalary plates symmetrically placed middorsally, while in

SYSTEMATIC ACCOUNT 29

Heterodinium the intercalary plate is always on the left shoulder. It is separated
from Peridinium by many other well defined characters, such as the incomplete-
ness of the girdle, the sculpturing, and the ventral pore, which is a much more con-
stant and definite structure than it is even in Gonyaulax. Some species of
Heterodinium such as H. spiniferum and H. murrayi approach some species of
Gonyaulax, for example, G. triacantha, in superficial appearance, but the girdle
and plate formula are quite different.

In many ways this is one of the more specialized and highly evolved genera
in the Peridinioidae. Its extreme rarity of individuals, the delicate hyaline theca,
the feeble development of chromatophores, the incompleteness of the girdle,
suggest that degeneration has to some extent accompanied this speciaUzation
which may be correlated with the tendency of many of its species to live in the
deeper, less illuminated levels of the tropical seas.

Heterodinium differs from DoUchodinium in lacking the anterior inter-
calary plate 1*, in having 4 instead of 3 apicals, and in having 6 instead of 7
postcingulars.

Key to the subgenera of Heterodinium Kofoid

1. Body spheroidal or rotund; antapical horns absent or feebly developed as spines Sphaerodinium.

1. Body elongated, flattened dorsoventrally with strong antapical horns 2

2. Epitheca narrowed towards the truncated apex Heterodinium.

2. Epitheca expanded, scoop-like with rounded apex Platydinium.

Subgenus Sphaerodinium Kofoid
Plate 13; Plate 15, fig. 1-10

Sphaerodinium Kofoid, 1906a, p. 350; Lindemann, 1928, p. 96.

The body is spheroidal or rotund, always circular at the girdle. Antapical
horns, when present, are always small, in the form either of small spines or short
hollow horns, less than 0.25 transdiameter in length.

Ten species (Plate 15, fig. 1-10) are included in the subgenus: H. kofoidi
Schiller {iion H. Kofoidi Pavillard = H. pavillardi nom. sp. \\oy.),H. sphaeroideum
Kofoid, H. doma Kofoid, and H. calvmn Kofoid, constituting the kofoidi group;
H. minutum Kofoid and Michener, H.obesum Kofoid, H. murrayi Kofoid, H.
milneri (Murray and Whitting), H. superbum Kofoid, and H. globosuvi Kofoid,
constituting the minutum group.

30 THE DINOFLAGELLATA

The type species is H. sphaeroideum Kofoid (1906a).

Key to the species of the subgenus Sphaerodinium Kofoid

1 . Girdle without overlap 2.

1 . Girdle with overlap 3.

2. Without antapical spines or horns 4.

2. With antapical spines or horns 5.

4. Distal end of girdle displaced posteriorly 6.

4. Girdle horizontal, not distally displaced sphaeroideum Kofoid.

6. Body small, length, 20m kofoidi Schiller.

6. Body larger, length, 70m 7.

7. Antapex rounded, postcingular rim not protuberant iloma (Murray & Whittinq).

7. Antapex flattened, postcingular rim protuberant calrum Kofoid.

5. Antapicals subequal superbum Kofoid.

5. Antapicals very unequal globosum Kofoid.

3. No apical horn, body globose, acicular spines minvium Kofoid & Michener.

3. Apical horn more developed, spines finned 8.

8. Apical horn well developed, 2 or 3 antapicals 9.

8. Apical horn scarcely emergent, 4 antapicals milneri (Murray & Whittino).

9. With 2 left antapicals on projecting lobe obesuiii Kofoid.

9. With 1 left antapical and no lobe murrayi Kofoid.

The kofoidi group
Plate 1, fig. 1-3, 8, 9; Plate 13; Plate 15, fig. 1-4

No apical horn, and no antapical spines or horns.

This group contains four species, H. kofoidi Schiller, H. sphaeroideum Kofoid,
H. doma (Murray and Whitting) and H. calvum Kofoid. The last two only,
occur in collections of the Expedition.

Heterodinium DOMA (Murray and Whitting)
Plate 1, fig. 8, 9; Plate 15, fig. 3

Peridinium doma Murray & Whitting, 1899, p. 327, pi. 30, fig. 3.
Heterodinium doma Kofoid, 1906a, p. 352.

Diagnosis: — A medium-sized, spheroidal species without horns or spines;
length 1.07 transdiameters; epitheca flattened ventrally; hypotheca hemispheri-
cal with trace of flattening at the antapex; girdle wide, without posterior rim,
furrow scarcely indented; surface reticulate, spinous. Length, 80 m- Rare in
the Eastern Tropical Pacific, in the Mexican Current, Easter Island Eddy, and
South Equatorial Drift.

Description: — This is a medium-sized species, spherical except for a slight
flare of the epitheca as it passes into the prominent precingular rim of the girdle,
and for the flattening of the ventral face of the epitheca and a very slight flatten-
ing of the antapical region of the hypotheca. There is only a suggestion of

SYSTEMATIC ACCOUNT 31

angularity in the outline of the body. The epitheca is a bit asymmetrical with
its right shoulder thrown up apically and the left with a slight angle at the apical-
precingular suture. The ventral face is flattened and the dorsal symmetrically
rotund. The epitheca is a trifle larger than the hjrpotheca by about 0.5 girdle
width. The apex, marked by the apical pore, is tilted ventrally about 10°.

The hypotheca is a little less than a hemisphere, flattened on the ventral
face but not much excavated, and contracted distally a little more on the right
than on the left side. The antapex in lateral view is broadly rounded and in
the ventral somewhat flattened.

The girdle is submedian, wide, being 0.12 transdiameter across, has a very
wide (0.6 its width) overhanging anterior rim, and only a trace of a posterior
ridge. It is displaced distally its width. The furrow is only slightly and un-
evenly indented, more dorsally than ventrally.

The sulcus is very short, narrow, deep, and sinuous and it does not extend
into the epitheca. Its total length is 0.25 transdiameter. The flagellar pore is
large, irregularly circular.

The plates are normal, and sometimes separated by wide, smooth intercalary
bands. The ventral pore is broadly reniform and its concavity is directed antero-
dextrally. The surface of the plates is everywhere covered by a heavily marked,
fairly regular reticulation except on the intercalary bands. There are about 25
polygons along the precingular ridge. Each polygon has a central pit and here
and there the theca is spinose, along the suture lines, the spines arising at the
junctions of the ridges forming the reticulation.

The cell contents were seen in only one individual in which they were col-
lapsed in a granular mass less then 0.5 the transdiameter in longest diameter. In
this mass there was a yellowish brown, eUipsoidal chromosphere, 0.35 trans-
diameter in longest diameter and a nucleus with minute moniliform granules.
It was ellipsoidal and about 0.16 transdiameter in its longest axis.

Dimensions: — Length, 80 m! diameter at the girdle, 78 /x. An individual
figured by Murray and Whitting (1899) was only 58 m long.

Comparisons: — The heavy reticulate and spinose surface markings dis-
tinguish this from all species of similar form in the .subgenus Sphaerodinium. The
angularity of the hypotheca is much less than in H. calvum, the apical pore is
more deflected ventrally, and the ventral surface less deeply excavated than in
that species. Since the spherical form is better preserved than in H. calvum, we
regard it as less differentiated than that species, although the latter species has
progressed further in surface markings.

32 THE DINOFLAGELLATA

Murray and Wliitting's (1899, pi. 30, fig. 3) figure of this species resembles
the specimens from the Expedition in the pattern and completeness of the reticu-
lation, the general form of body, ventral suture, and location of ventral pore. It
differs from those of the Expedition in smaller size (58 ^ as compared with 80 n),
and in a more emergent postcingular ridge. One of our specimens (Plate 1, fig. 8)
has a sUghtly emergent ridge, but not as much as in their figure.

The type locahty is 34°-39° N., 32°-39° W. in the Atlantic west of the
Azores (Murray and Whitting, 1899).

Occurrence: — Heterodinium doma is recorded (Plate 13) at five of the 127
stations. There are 1, 0, 0, 4, 0, and 0 stations on the six Unes of the Expedition.
Of these five stations, one (4590) is in the Mexican Current, three (4695, 4697,
4699) are in the Easter Island Eddy, and one (4701) is in the South Equatorial
Diift. No specimens were taken in surface hauls. All five records are from
hauls from 300-0 fathoms.

The temperature range of these five stations at the surface was 72°-83° and
the average was 75.8°.

The frequency in all cases was less than 1%.

It was reported by Murray and Whitting (1899) from two stations in the
warm temperate Atlantic between 34°-39° N. and 32°-39° W. in surface waters
at 60°-66° in March.

In the Pacific all records but one (4590) in the Mexican Current are grouped
in and near the Easter Island Eddy. In conjunction with the Atlantic records
this species is eupelagic, confined to deeper levels, and rather widely eurythermal
within tropical and warm temperate waters, though the evidence from the Ex-
pedition material by itself supports a restriction to warm-tropical deeper waters.
The specimens from the two regions are so similar as to justify inclusion in one
species.

Heterodinium calvum Kofoid
Plate 1, fig. 1-3; Plate 15, fig. 4

H. calvum Kofoid, 1907a, p. 177, pi. 7, fig. 43.

Diagnosis: — A medium-sized subspheroidal, somewhat angular species
without horns or spines; length equals transdiameter; epitheca hemispherical;
hypotheca with obliquely flattened antapex; furrow indented; surface smooth,
porulate. Length, 75 ix. Rare in the Eastern Tropical Pacific, in the California
Current, Easter Island Eddy, and the South Equatorial Drift.

SYSTEMATIC ACCOUNT 33

Descriptio)i: — In this rather small species the body is almost spheroidal;
the length almost exactly equals each of the diameters at the girdle, which divides
it equally. The epitheca is a low dome, flattened and excavated a little on its
ventral face, evenly rounded at the apex, and with only a slight flare at the girdle.
The ventral area is small with a large, reniform pore with the concavity facing
right.

The h3T)otheca is rather angular; being excavated ventrally, a little com-
pressed laterally, and obliquely flattened dorsoposteriorly.

The girdle is very wide and the furrow fairly deeply impressed (0.5 its width),
with exceptionally well developed cingular ridges, the anterior one overhanging,
and the posterior less developed than the anterior. Its postcingular lim is
angled at the postcingular sutures on the dorsal side, but the precingular one is a
continuous spiral. It is displaced its width or more.

The sulcus is a very narrow, deep groove and extends only a little way behind
the posterior rim of the distal end of the girdle from which it is parted by plate 7".

The plates are quite normal in arrangement. Postcingular 7" ' extends to
the precingular ridge and lies at the right of the sulcus in the ventral trough.
The spacing of the pores and traces of sutures in the furrow indicate seven girdle
plates. The plates are marked in the hypotheca by the clearly defined ridges at
the sutures, serrated around antapical 1" " only. On the dorsal side of the epi-
theca the sutures are less distinctly ridged but are outUned by light bands. The
thecal wall is sparsely and uniformly porulate, but has no surface reticulations.
There are 32 pores across the dorsal precingular ridge and a single row in the
furrow.

Dimensions: — Length, 75 n; diameter at the girdle, 75 m; girdle width, 10 n.

Comparisons: — Heterodinium calvum is the largest species in the subgenus
Sphaerodinium. It has developed the angles on the postmargin at points where
antapical spines or horns emerge in the subgenus Heterodinium. It is distin-
guished from the other spheroidal and hornless species by this angularity of the
postmargin of the hypotheca, a character which is less evident in H. doma.
These two species are very much alike in form, but H. calvum differs from H.
doma in the entire absence of reticulations and in the much greater development
of the postcingular rim of the girdle, and greater angulation.

The type locality is Station 4691 in the Easter Island Eddy.

Occurrence: — H. calvum is recorded (Plate 13) at eight widely separated
stations of the 127 stations. There are 1, 0, 0, 1, 1, 5, and 0 stations respectively
on the six Unes of the Expedition. Of these eight stations, one (4583) is in the

34 THE DINOFLAGELLATA

California Current, two (4691, 4695) are in the Easter Island Eddy, and five
(4721, 4724, 4730, 4734, 4739) are in the South Equatorial Drift.

It was taken at one station only (4583) in a surface haul. All others are
from hauls from 300-0 fathoms.

The temperature range at these eight stations at the surface was 72°-83°,
and the average was 77°, a relatively high average.

The frequency at all the eight stations is less than 1%. This species has
thus far not been found elsewhere.

It is a rare, eupelagic, stenothermal species of the Eastern Tropical Pacific,
but is not limited to the deeper levels.

The minutum group
Plate 1, fig. 4-7; Plate 2; Plate 3, fig. 1, 2, 4-6; Plate 4; Plate 13; Plate 15, fig. 5-10

Apical horn more or less developed ; antapical spines or horns present.

This group contains six species (Plate 15, fig. 5-10), He.terodinium minutum
Kofoid, H. obesum Kofoid, H. murrayi Kofoid, H. milneri (Murray and
Whitting) H. superhum Kofoid, and H. globosum Kofoid, all of which occur in
the collections of the Expedition.

Heterodinium minutum Kofoid and Michener
Plate 1, fig. 4-7; Plate 15, fig. 5

Heterodinium minuhmi Kofoid & Michener, 1911, p. 285.

Diagnosis: — A minute spheroidal species; length of body without spines
1.0 transdiameter, with premedian (at 0.3 total length) overlapping girdle, dis-
placed 2 girdle widths; no postcingular list, furrow slight; two equal, oblique,
acicular antapical spines and one similar ventral spine; surface smooth, sparsely
porulate. Length, 40 ii. Rare in the Eastern Tropical Pacific in the Easter
Island Eddy and South Equatorial Drift.

Description: — In this minute and rather unusual species the body is an al-
most perfect sphere, modified only by the precingular ridge and sulcal furrow.
The epitheca is a flat dome of 0.4 transdiameter in altitude, flaring sUghtly in the
precingular ridge at the girdle.

SYSTEMATIC ACCOUNT 35

The h^-potheca is large and rotund, 0.6-0.7 transdiameter long, with sym-
metrically rounded antapex. Below the sulcus is an excavation bounded by
curved lateral ridges; the posterior end of each is continued into a short, acicular
antapical spine, deflected ventrally 30° from the major axis and about 2 girdle
widths in length. Further up on the left ridge at the end of the sulcus is a similar
ventral spine.

The girdle is horizontal except in its displaced distal fourth. Its anterior
rim is widely overlapping, but not curved downward. The postcirigular rim is
wholly lacking. The girdle is displaced 2.0 its width, being uniformly deflected
in its distal quarter, and has an overlap of about its width. The furrow is but
feebly impressed into the body wall, somewhat less distally than in its pi'oximal
region, and more distinctly anteriorly.

The sulcus is well developed, having a total length of 0.3 the length of the
body. It is bounded by thickened ridges, raised into hyaline fins below the girdle,
and continued on each side of the excavation towards the antapex. Below its
posterior end a spreading, curved ventral excavation extends nearly to the anta-
pex. Its distal width is 0.28 transdiameter.

No suture lines have been observed but the plating is indicated by the ar-
rangement of the poi'es which are minute and few on each plate and only 12-13
across the dorsal side at the girdle. Faint reticulations mark the girdle plates
and a short linear series runs down the right side of the posterior half of the sulcus.
A low rim surrounds the apical and ventral pores. The latter is ellipsoidal and
connected by a rib with the precingular rim.

The plasma is coarsely granular, and in one individual (Plate 1, fig. 7) a
large, brown, spherical chromosphere was seen in the posterior end. Its spheri-
cal nucleus, 0.28 transdiameter in diameter, was centrally located. Highly re-
fractive, spherical amyloid bodies smaller than the nucleus lay adjacent to the
chromosphere and a very large pusule filled the left central region. The wall is
noticeably thick.

Dimensions: — Length, 40 m; transdiameter, 40 m; antapical spines, 5 m-

Variation: — One specimen from Station 4724 had no antapical spines
though otherwise quite typical. The proportions and surface of the three speci-
mens seen were uniformly similar.

Comparisons: — Heterodinium minutum is closely related to H. sphaeroideum,
H. kofoidi, and other spheroidal species. This one differs in the possession of
spines, in the overlapping and displaced girdle, as well as in the pattern of the
thecal wall. It is a transition form between the kofoidi and minutum groups.

36 THE DINOFLAGELLATA

The type locality is Station 4697 in the Eastern Island Eddy.

Occurrence: — Heterodinium minutum was taken (Plate 13) at only three of
the 127 stations. There are 0, 0, 0, 2, 1, and 0 stations on the six lines of the Ex-
pedition. Of these three stations, one (4697) is in the Easter Island Eddy, and
two (4701 and 4724) are in the South Equatorial Drift. All records are from
hauls from 300-0 fathoms.

The frequency was always less than 1%.

The surface temperatures were 72°, 75°, and 79° respectively at the three
stations.

This species is eupelagic in the Eastern Tropical Pacific and was not taken
in surface collections.

Heterodinium obesum Kofoid
Plate 2, fig. 4-6; Plate 15, fig. 6

Heterodinium ohesum Kofoid, 1907a, p. 1S3, pi. 8, fig. 50.

Diagnosis: — A minute obese species with globose midbody; its length, ex-
cluding spines, 1.2 transdiameters; short, prominent apical horn; two antapical
spines with a large protuberance at the base of the left one; girdle overhanging,
displaced 2.0 its width; surface sparsely and coarsely reticulate and porulate.
Length, 55 (50-60) m- Rare in the Eastern Tropical Pacific in the Panamic Area
and the South Equatorial Drift.

Description: — This is a very small .species with a rotund, obese body, 1.3
transdiameters in length, and circular at the girdle. The epitheca is a low cone
of about 80° with concave sides laterally and ventrally, and convex locally dor-
sally. It is produced into a stout apical horn displaced ventrally from the major
axis 0.18 transdiameter, making its total altitude 0.6 transdiameter. The apex
is obliquely truncated, sloping ventrally. The horn is 0.5 the total altitude in
length and is itself a truncated cone of 22°. A ventral area is scarcely defined but
the pore is present as usual. It is ellipsoidal witli the long axis subvertical and
in Une with the major axis. It is 0.33 of the altitude above the precingular ridge.

The hypotheca is larger than the epitheca, 0.8 transdiameter long, rotund,
and with a rather deep ventral excavation. It is widest about the middle of the
postcingular plates. The left side is protuberant below the girdle, the right is
symmetrical, and the dorsal and ventral subhemispherical, but the ventral has
a shorter radius than the dorsal.

SYSTEMATIC ACCOUNT 37

The most striking development in this species is the prolongation of the body
in a stout, left, antapical protuberance, so stout as to suggest the avoidance of the
word "horn" as its designation. Morphologically it has the location of a left
antapical horn, but structurally it is imlike the horn in any other species in the
genus in that it is a broad, blunt process instead of a tapering one. It is a low
subhemispherical dome, asymmetrically flattened, longer distally on the inner
ventral region, and merging with the body more within a shorter distance dor-
sally than ventrally. Another reason for refraining from using the designation
"horn" is the fact that it bears on its distal inner face a pair of antapical spines,
the larger one of which is the homologue of the right spine. It is a rule in the
genus for either spines or horns to be present when there are any antapical
extensions. No other species has a spine on one side and a horn on the
other.

The left antapical region has two oblique spines united by a common fin ; the
right has a single with a narrow fin.

The girdle is horizontal except in its distal fourth, which is so deflected pos-
teriorly that its displacement is twice its width. There is considerable overlap at
the ends, in fact nearly two girdle widths. The anterior rim is heavy, forming a
sharp, projecting shelf which in one individual had a very low ribbed fin. The
posterior rim is wholly wanting. The furrow also is completely lacking.

The sulcus is normal except for its great obliquity (45°), and is continued into
the ventral excavation of the hypotheca which is also, by reason of the overhang
of the girdle, much curved. It reaches the squarish postmargin where its width
is 0.18 transdiameter.

The plates are normal. The left intercalary is rather large. Precingular
7 " is very narrow and crowded against the sulcus. The reticulations of the
theca are imperfectly and unequally developed in all six specimens seen, being
continuous only in the plates of the epitheca, posteingulars 1' " and 2' ", antapical
2" ", and the girdle plates. The reticulations are relatively very coarse, about 16
across the dorsal side at the girdle. The wall is porulate, some polygons of the
reticulum are without pores, many have one pore each, and the larger ones may
have two or three. The suture lines are bordered by wide, smooth, hyaline
bands of the intercalary type, especially on the epitheca.

Dimensions: — Length, 50 (55-60) m; transdiameter, 40 m; spines, 5 /z.

Variation: — One of our specimens taken at the same station (4734) as the
one figured in Plate 2, figures 4-6, had a wider girdle, with a slight furrow and a
more tapering antapical prolongation with the reticulations much less developed,

38 THE DINOFLAGELLATA

except in the girdle region. A specimen from Station 4638 had an apical horn
proportionately 25% longer than the one figured on Plate 2.

Comparisons: — This species is marked off from all others in the genus by the
posterior prolongation. It otherwise has marked resemblances to H. globosum
and H. murrayi. H. minulum and H. milneri share with this species the dis-
placed overhanging girdle.

The type locality is Station 4734 in the South E(iuatorial Drift.

Occurrence: — Heierodiniwn obesum is recorded (Plate 13) at six of the 127 sta-
tions with a total of seven specimens. There were 0, 0, 2, 1, 3, and 0 record
stations respectively, on the six lines of the Expedition. Of these six stations, one
(4638) is in the Pananric Area and the other five (4681, 4701, 4730, 4732, 4734) are
in the South Equatorial Drift. They were taken only in hauls from 300-0
fathoms, except for one at Station 4681 from 800-0 fathoms.

At Station 4681 the frequency reached 1%. At this, and all other sta-
tions, single specimens only wei'e found, except at Station 4734, where two were
ultimately discovered.

The temperature range of these five stations at the surface was from 68°
to 84° and the average was 76.7° F.

Its absence from the Peruvian Cvu-rent and from surface collections is alike
noteworthy. The limited data suggest a stenothermal limitation of this eupe-
lagic species to the deeper waters of the tropical currents.

Heterodinium murrayi Kofoid
Plate 2, fig. 1-3; Plate 3, fig. 3; Plate 15, fig. 7

Pcriilinium Iri/jos Murray & Whitting, 1899, p. 327, pi. 30, fig. 4a, b; Ostenfeld & Paulsen, 1904,

p. 167.
non Peridinium tripos Ehrenberg, 1834, p. 272.
Heterodinium murrayi Kofoid, 1906a, p. 343, 353.

Diagnosis: — A minute, top-shaped, symmetrical species, length, excluding
spines, 1.16 transdiameters, with a short, stout apical horn; hypotheca hemi-
spherical, with 3 aciculate spines; girdle overhanging, displaced 2.0 its width;
surface fully reticulated. Length, 58 p. Rare in the tropical Atlantic and
in the Mexican and Peruvian Currents and the South Equatorial Drift of the
Pacific.

Description: — In this small species the body apart from the apical horn is
very rotund, but this structure gives it the form of a stout top. It is circular at
the girdle which divides the midbody subequally. Its total length is 1.2 trans-

SYSTEMATIC ACCOUNT 39

diameters. The epitheca is conical (70°) and drawn out into a stout, asynxmetri-
cally conical (30°) horn, squarely truncated at the apex, 0.2 transdiameter long,
tilted to the left slightly, and more concave dorsally than ventrally. The right
outline is sigmoid, the left straight to concave. The ventral area is a subtrian-
gular hyaline region just above the proximal end of the girdle, irregularly shaped,
with the pore near the anterior end. The ventral pore is broadly ellipsoidal and
quite minute.

The hypotheca is subhemispherical, slightly inflated to the right. The post-
margin is broadly rounded and bears three aciculate, finned spines, 0.2 trans-
diameter long, two of them symmetrically placed 0.35 transdiameter apart on
the antapex, and the third ventrally and to the left some distance from the edge
of the postsulcal excavation.

The girdle is median, horizontal in dorsal view, and displaced 2.0 its width
with an overlap of a girdle width. The furrow is not impressed but the pre-
cingular rim forms a steeply overhanging shelf with arched lower surface. The
posterior rim is wanting entirely.

The sulcus is normal, 0.43 of the transdiameter in length, with a slight sig-
moid curve, tilted to the right 20° from the axis and guarded by a low sinistral
list. The postsulcal excavation is not differentiated.

The plates conform closely to type; the anterior intercalary (Plate 3, fig. 3)
is a quadrilateral and postcingular 7" ' laterally expanded. The suture lines are
in some places "marked by rows of small polygonal reticulations, and elsewhere by
hyahne, plain intercalary zones between the coarse-meshed markings which
cover the body generally including the girdle. There are 18 polygons across the
dorsal side at the girdle. Generally there is a single pore in the center of each
polygon.

The plasma is finely granular. In one specimen there were three brownish
chromospheres which stain deeply in Ehrlich's haematoxyUn. The nucleus is
subcentral, elUpsoidal, 0.16 transdiameter in longest diameter and resists staining
(fixed in formahn) in the Ehrlich's stain. In this specimen (Plate 2, fig. 3) there
was a cluster of fine filamentous rhabdosomes in the apical plasma and in the
space between theca and plasma. Some of them were escaping with plasma
through the apical pore.

Dimensions: — Length, 58 fi; diameter, 48 m; major antapical spines, 10 m-

Variation: — The individual figiu-ed by Murray and Whit ting (1899) has
the apical horn and the spines much shorter than in our material. The reticula-
tion is much more heavily marked, and the overhang of the girdle is a Uttle

40 THE DINOFLAGELLATA

greater, and the postsulcal excavation more marked. These differences may be
more than mere intraspecific variations. However, they occur in well known
variable features and there is a sufficient similarity between their figure and ours
in girdle, spines, and general habitus, so that we hesitate to regard our material as
specifically distinct from theirs.

Comparisons: — This is a species of the same type as H. obesum but has more
development of apical horn and surface markings. It differs from H. milneri in
being less rotund, in having longer apical and antapicals, and also in more numer-
ous, smaller reticulations. From the higher members of the series, H. superbum
and H. globosum, it differs notably in having finned, aciculate antapical spines,
instead of hollow antapical horns formed as extensions of the theca and its
cavity.

Synonymy: — This species was first described by Murray and Whitting
(1899) as Peridinium tripos. This specific name is preoccupied in Peridinium by
P. tripos Ehrenberg (1834). Kofoid (1906a) therefore replaced it by murrayi
and transferred the species to his new genus Heterodinium. Schiller (1916, p.
209) restores the specific name tripos in Heterodinium for Murray and Whitting's
species but without stating the grounds.

The type locahty is 14°-31° N., 38°-58° W. in the Atlantic (Murray and
Whitting, 1899).

Occurrence: — Heterodinium murrayi is recorded (Plate 13) at six very widely
scattered stations of the 127 stations of the Expedition. There were 1, 2, 1, 0, 2
and 0 stations respectively on the six lines of the Expedition. Of these six, one
(4594) is in the Mexican Current, two (4667, 4670) are in the Peruvian, and three
(4679, 4722, 4724) are in the South Equatorial Drift. At Station 4670 it was
taken in a haul from 800-0 fathoms, elsewhere only in hauls from 300-0 fathoms.

It is very rare, the frequency always being less than 1%.

The temperature range at these six stations at the surface was from 68°-84°,
and the average was 73.6°.

Murray and Whitting (1899) record the species from the tropical Atlantic
between 14° and 31° N. and 38° and 58° W. at four different stations in March
and April from surface collections at 67° and 78°. Ostenfeld and Paulsen (1904,
p. 167) report it as ^'Peridinium tripos Murray and Whitting" as very rare in
the North Atlantic at 59° N. 16° W. in surface temperature of 48° F. These
records indicate a northward extension in Gulf Stream water.

This species is eupelagic and eurythermal. It evidently has a wide distribu-
tion, is either more abundant or occurs more freely near the surface than most of

SYSTEMATIC ACCOUNT 41

the species in the genus, and has a more northerty range. It was, however, not
found in the colder Peruvian Current in the collections of the Expedition, an ad-
ditional reason for the suspicion that the form from the Eastern Tropical Pacific
may be specifically distinct from that in the Atlantic. The matter can be de-
cided when more material from the Atlantic can be examined.

Heterodinium milneri (Murray and Whitting)
Plate 3, fig. 1, 2, 4-6; Plate 15, fig. 8

Peridinium milneri Murrat & Whitting, 1899, p. 327, pi. 29, fig. 3a, b.
Heterodinium milneri Kofoid, 1906a, p. 353.

Diagnosis: — A stout subspheroidal species, with a low, stout apical horn
and four stout, finned antapical spines; girdle displaced 2.0 its width with 2 girdle
widths overhang; theca very coarsely reticulated. Length, 65 ix. Rare in the
tropical Atlantic and Pacific in the Mexican and Peruvian Currents and the South
Equatorial Drift.

Description: — This is a small, very stout, subspheroidal species, subcircular
in section at the girdle, length including the spines 1.22 transdiameters, with
epitheca and hypotheca subequal. The epitheca is dome shaped, a low cone of
100° with almost straight sides in dorsal or ventral view, except towards the apex
which is drawn out into a low stout horn with a cupped apical pore. The ventral
face is slightly concave and the dorsal slope is 1 .35 greater than the ventral.

The hypotheca is more rotund, with evenly rounded antapex except when
tilted ventrally. The antapical region has a ventral tilt which deflects the antapi-
cal spines about 20° from the axis of the hjT^otheca as a whole. Because of the
absence of the postcingular ridge, the hj'potheca appears to exceed the epitheca,
but, if the girdle plates are excluded, their equality is more evident. It bears the
four stout antapical spines each a girdle width long. The right accessory is small
in our specimen (Plate 3, fig. 4). The relations of these spines are not clearly
shown in Murray and Whitting's (1899, pi. 29, fig. 3b) figure. There are two
proximal, more dorsally located spines, the homologues of the two antapicals in
H. minutum, and two slightly smaller, more ventrolaterally placed, accessory
spines.

The girdle is premedian in its proximal 0.25, median dorsally, and slightly
postmedian in its distal 0.25. It forms a descending spiral, displaced 2.0 its
width, with an overlap of at least 2 girdle widths. The precingular ridge is
prominent, the postcingular wholly undeveloped. The precingular ridge is

42 THE DINOFLAGELLATA

relatively low, less than 0.5 girdle width wide, is almost horizontal below, and has
a very narrow ribbed list.

The sulcus is a deep, sinuous groove with thickened edges forming a sigmoid
curve with enlarged ends, 0.4 of the total length, without a distinct postsulcal
trough.

The anterior intercalary plate is peculiar in being very small and marked
only by two tiny pores or pits (Plate 3, fig. 2, 4).

The thecal wall has a very coarse reticulation of polygons, each with a central
pit, which fills the central area of each plate, being absent in the wide smooth
intercalary border along the suture lines. The thickenings forming the pattern
are continued as short ribs on the precingular ridge. The ventral pore in the
epitheca is located unusually far anterior, at the base of the small apical horn. It
is but little larger than the pores in the adjacent polygons.

The cell contents of one specimen (Plate 3, fig. 1) consisted of a finely granu-
lar cytoplasm crowded with hyaline, radially arranged, homogeneous, stout, rod-
like bodies of unknown nature. There were seven spheroidal or ellipsoidal
chromospheres of various sizes clustered in the center and an ellipsoidal nucleus
with moniliform chromatin threads.

Dimensions: — Length, 65 ix; transdiameter, 55 m; spines 8 m.

Comparisons: — Heterodinium milneri shares many characters with H.
murrayi, the rotund midbody, the displaced overhanging girdle, and the presence
of finned spines. But the apical horn is here less developed and there are four
instead of three antapical spines, the svu'face markings of H. murrayi iorm a
complete network over the whole surface, and its antapical spines are longer and
more slender. Furthermore the apical pore is much farther anterior in H. milneri
than in H. murrayi.

Synonomy: — Murray and Whitting (1899) described this as Peridinium
milneri and Kofoid (1906a) transferred it to Heterodinium.

The type locality is 29°-31° N., 42°-44° W., in the Sargasso Sea (Murray
and Whitting, 1899).

Occurrence: — Heterodinium milneri (Plate 13) is recorded at nineteen of the
127 stations. There are 1, 0, 8, 5, 4, and 1 station respectively on the six lines of
the Expedition. Of these nineteen stations, one (4583) is in the Mexican fur-
rent, one (4676) in the Peruvian Current, fifteen (4679, 4680, 4681, 4683, 4685,
4686, 4689, 4705, 4707, 4711, 4722, 4724, 4732, 4734, 4740) are in the South
Equatorial Drift, and two (4697, 4699) are in the Easter Island Eddy. At only
three stations (4583, 4680, 4686) is the species recorded in surface collections.

SYSTEMATIC ACCOUNT 43

All other records are from 300-0 fathoms except those at 4681 and 4689 which
are from 800-0 fathoms only. There is also a record at 800-0 fathoms at Station
4724.

The temperature range was 68°-83° and the average 74.1°.

The frequency was 1% or less at all record stations, a total of 20 specimens
having been seen.

The aggregation of 17 of the 19 record stations in the South Equatorial Drift
(15) and adjacent Easter Island Eddy (2), the presence of only a single record in
the Peruvian Current, and its absence from the Panamic Area, is indicative that
this is a tropical species with its center of distribution in the large central area of
the Eastern Tropical Pacific occupied by the South Equatorial Drift. In fre-
quency of record (19) it is approached in the genus only by H. curvatum (17) and
H. (jesliculatuin (16), and surpassed only by H. rigdenae (23), all of which have
their centers of record in the South Equatorial Drift along with H. milneri, but
unlike it, both H. rigdenae and H. gesticulatum occur also in the cooler Peruvian
Current and Panamic Area more widely, and are to this degree less typically
tropical than H. milneri.

Murray and Whitting (1899) reported this species from the tropical Atlantic
between 29° and 31° N. and 42° to 44° W. at eleven record stations in November,
December, and March, in temperatures of 67° to 81°.

This species is eupelagic, eubathmic and stenothermal, with a limitation to
the warmer tropical seas, and is only occasionally taken in surface waters, three
times by this Expedition and four times by Murray and Whitting. It is rare,
though widely distributed.

Heterodinium superbum Kofoid
Plate 4, fig. 5-7; Plate 15, fig. 9

Heterodiiiiwn superbum Kofoid, 1907a, p. 185, pi. 8, fig. 49.

Diagnosis: — A small species of robust habit; with dorsoventrally flattened
apical horn scarcely developed; hypotheca angular; small, subequal, acute,
antapical horns; girdle 0.12 transdiameter in width, displaced its width but no
overhang, with very low postcingular rim; sulcus nearly straight ; surface reticulate
throughout. Length, 75 m- Rare in the Eastern Tropical Pacific in the Easter
Island Eddy.

Description: — This is a small robust species, subglobose and but sHghtly
elongated, its length 1.3 the transdiameter, 1.4 the dorsoventral, divided equally

44 THE DINOFLAGPXLATA

by the girdle. The epitheca is subconical (80°-90°), dorsoveuti-ally compressed
towards the truncated apex and flaring sUghtly at the girdle. Its outlines are
convex except distally on all faces. There is only an indication of an apical horn,
except in lateral view (Plate 4, fig. 6) in which it is asymmetrically conical (30°)
and less than a girdle width in length with squarely truncate apex. The ventral
area is a small rectangle displaced to the left with a reniform pit or ventral pore
at the center with the concavity at the right.

The more rotund h>'potheca is rather angular at the postcingular and antapi-
cal sutures. Its ventral face is flattened and excavated, its dorsal side broadly
rounded and flattened dorsal to the ventrally deflected antapical horns.

There are two short, stout, conical antapical horns, acutely pointed, the left
stouter (35°) than the right (25°), and a girdle width in length. The right horn
is a bit the shorter. They are deflected ventrally 25° from the vertical axis of the
body. They are hollow extensions of the body, not solid spines as in H. milneri.

The girdle is very wide, 0.12 transdiameter in width, median in location, and
displaced distally its width. Its precingular rim is heavy and overhanging with
a very narrow ribbed list on its edge. The lower surface of this ledge is flattened,
rather than curved, with its slope exposed to view. The postcingular ridge is
developed as a shghtly protuberant angle marked by a row of small reticulations.
The ends of the girdle scarcely meet, overhang being wholly absent. The furrow
is indented as an angular trough nearer the precingular than the postcingular
rim.

The sulcus is quite straight, almost vertical, and very narrow except for a
small expansion at the proximal end of the girdle where the flagellar pore opens.
A low list borders the right side of the posterior sulcus below the pore. There is
a wide straight, very deep, postsulcal trough, 0.25 transdiameter in width, with a
convex postmargin between the antapical horns.

The plates are normal. The anterior intercalary 1^ is very large and is ex-
tended almost to the apex. Postcingular 7" ' is long and narrow and crowded
into the ventral excavation. Strong, ridged sutui'e lines separate the plates.
The lines on the hypotheca contain a row of small quadrilateral reticulations.
The surface generally is uniformly and rather coarsely reticulate. Each polygon
has a small pore at the center. A double row of quadrilateral polygons fills the
entire girdle.

Dimensions: — Length, 75 m; transdiameter, (30 m; dorsoventral diameter,
56 ti; length of left antapical horn, 12 ix.

Comparisons: — This species is the first of the minulum series to have antapi-

SYSTEMATIC ACCOUNT 45

cal horns instead of spines. The shape of body is more rotund posteriorly than in
H. milneri. In this respect it closely resembles H. globosum, but differs in the
well developed surface markings and in the slight emergence of a definite apical
horn. Its antapicals are also more nearly equal. In some characters, such as the
flattening of the apical region, the bifurcated form of the antapex, and develop-
ment of reticulations, it approaches the subgenus Heterodinium, but on account
of its globose body, it belongs more naturally to the subgenus Sphaerodinium.

The type locality is Station 4699 in the Easter Island Eddy.

Occurrence: — There is only a single record (Plate 13) of Heterodinium
siiperbum at Station 4699 on the fourth line of the Expedition, in the Easter
Island Eddy in a haul from 300-0 fathoms. The surface temperature there was
75° F. Only a single specimen has been seen.

Heterodinium globosum Kofoid
Plate 4, fig. 1-4; Plate 15, fig. 10

Heterodiuiwii globosum Kofoid, 1907a, p. 181, pi. S, fig. 51.

Diagnosis: — A large species with a globose midbody; length 1.5 trans-
diameters, small apical horn; stout unequal antapical horns and asymmetrical
postmargin; surface incompletely and very irregularly reticulated. Length,
110 (100-120) ju- Rare but widely distributed in the Eastern Tropical Pacific
in the Mexican and Peruvian Currents, Easter Island Eddy, and South Equa-
torial Drift.

Description: — The body of this rather large, rotund species is, apart from
the horns and sulcal depression, spheroidal, or shghtly elongated, and divided
equally by the girdle. Its length is 1.45 transdiameters. The epitheca is
broadly campanulate, with hemisj^herical base with flaring rim. It is produced
into a short, stout, asynmietrically conical (40°) apical horn with obliquely trun-
cated apex drawn out in a point in the dextroventral quadrant, which increases
its total altitude to 0.7 transdiameter. It flares abruptly at the girdle in the pre-
cingular rim and has only an indication of ventral flattening. A ventral area is
not defined in the surface markings but the usual ventral pore is present. It lies
as usual at the junction of the apical-precingular suture with the midventral
suture which is very considerably deflected to the left. It is broadly ellipsoidal
with its long axis in the oblique suture line.

The hj-potheca is more perfectly hemispherical than the epitheca except for
the deep ventral excavation and the two horns.

46 THE DINOFLAGELLATA

It bears the two short, stout, sharply pointed, unequal antapical horns.
Both are tilted ventrally about 30° and the tip of the left is curved ventrally.
The left is about 0.25 transdiameter long, and the right but half as much or less,
and somewhat more laterally deflected. The postmargin is asymmetricallj^ con-
cave and the distance between the bases of the horns is 0.35 transdiameter.

The sulcus is relatively smaller than in most species, slightly expanded about
the flagellar pore, and guarded laterally on each side by a low, hyaline list. Its
length is 0.3 transdiameter and the postsulcal trough is lost in the general ventral
excavation of the hypotheca. The svu-face is marked here and there by a verj'
irregular mesh work consisting of incompletely developed reticulations, some large
and marked with a central pit, some very small without a pit. The suture lines
are bounded by very wide, smooth intercalary bands. The locations and pattern
of the developing reticulations are noteworthy. In all specimens seen the mesh
is only in the earliest phase of emergence. It is uniformly best developed on the
ventral face and nearest the flagellar pore, in the girdle, on the ventral pro- and
postcingular plates, and especially on precingular 1". The mesh on the left side
is better developed than on the right, and on the left horn more than on the light.
The mesh starts about the periphery of each plate marking off the intercalary
zone and the polygons converge centripetally from this marginal ridge. Small
pitless polygons spread centrifugally from the marginal ribs into the intercalary
zones.

The cell contents in one individual observed in life consisted of fine homo-
geneous, very hyaline cytoplasm containing a large spheroidal, pale yellowish
green chromosphere, 0.5 transdiameter in diameter, and centrally located. At
its left was an ellipsoidal nucleus whose long diameter was 0.35 transdiameter
containing finely beaded chromatin (chromosomes). A large number of small,
subuniform oil droplets covered the anterior surface of the chromosphere. No
pusule was seen. A specimen stained in haematoxylin revealed finely granular
cytoplasm, no pusule, the nucleus and deeply stained chromosphere located as in
life, and, in addition, a bundle of subparallel, acicular rhabdosomes in the cyto-
plasm near the flagellar pore and two other stained bodies, possibly accessory
chromospheres adjacent to the major chromosphere. The whole cell is unusually
hyaline in life.

Dimensions: — Length, 110 (100-120) //; transdiameter, 85 m; right antapi-
cal, 14-22 M, and left, 3-6 m-

Comparisons: — This species shares with H. superbmn the presence of antapi-
cal horns, but differs from it in incomplete reticulations and lack of angularity.

SYSTEMATIC ACCOUNT 47

In shape it is nearly related to H. obesum; the two are remarkably similar in form
and surface markings, but H. obesum has antapical spines instead of horns, is
much larger, while H. globosum lacks entirely the characteiistic antapical pro-
tuberance and overhang and displacement of the girdle of //. obesum.

The type locality is Station 4699 in the Easter Island Eddy.

Occurrence: — Heterodinium globosum is recorded (Plate 13) at fourteen of
the 127 stations with a total of 14 specimens seen. There are 3, 0, 5, 3, 2, and 1
stations respectively on the six lines of the Expedition. Of these fourteen sta-
tions, three (4587, 4590, 4604) are in the Mexican Current, one (4676) in the
Peruvian Current, seven (4679, 4689, 4691, 4701, 4724, 4737, 4740) in the South
Equatorial Drift, and three (4692, 4697, 4699) in the Easter Island Eddy. The
species was taken at only three stations (4590, 4604, 4692) in surface hauls. It
was taken once (Station 4587) in a haul from 100-0 fathoms and once (Station
4689) from 800-0 fathoms, all other records being from 300-0 fathoms.

The temperature range at the fourteen stations was 69°-84° and the average
76.5°.

Only at two adjacent stations (4691, 4692) is the frequency 1%, at the other
twelve it is less.

This species is the largest in the minul'mn group, and in j^art for this reason is
retained more readily by the mesh of the silk net. It is surpassed in frequency by
H. milneri (19 records) in the minutum group, and by H. curvatum (17), H.fenes-
tratum (15), H. gesticulatum (16), and H. rigdenae (23) in the rest of the genus.
Its absence in the Panamic Area, the single record in the Peruvian Current, and
the high average temperature (76.5°), all indicate a stenothermal limitation to
warm tropical waters. It has a marked center of occurrence in the South
Equatorial Drift and is typically eupelagic with a preference for deeper waters.

Subgenus Heterodiniitm nom. subgen. nov.
Plate 15, fig. 11-25
Euheterodinnim Kofoid, 1906, p. 351; Lindbmann, 1928, p. 96.

The body is more or less elongated and flattened dorsoventrally. The
epitheca narrows towards the truncated apex and sometimes has a well defined
apical horn, the hypotheca is bifurcated into large, subequal antapical horns giv-
ing a superficial resemblance to the genus Peridinium. Type species Heterodin-
ium, scrippsi Kofoid (1906a).

48 THE DINOFLAGELLATA

This subgenus consists of three groups, the expansum group with contracted
apical horn ; the dispar group with no lateral contraction in the apical region into
a distinct horn in ventral view and with elongated epitheca and antapicals, and
the rigdrnae grouji with shorter epitheca and antapicals.

Key to the species of the stibgenus Heterodinium

1. With npiciil liorn set off from epitheca in ventral view. .2.

1. Apical horn not set off, ejntheca conical in ventral view .3.

2. Large species, length 240 ix, midventral suture very abruptly angled ... praetextum Kofoitl.

2. Smaller species, midventral suture nearly straight and vertical 4.

4. Lateral outlines of epitheca abruptly angled (ingulalum Kofoid and Michener.

4. Lateral outlines without abrupt angles 5.

5. Epitheca broadly and equally convex laterally, antapicals subvertical expansum Kofoid.

5. Epitheca unequal laterally, the right side slightly convex, the left less or concave 6.

(). Antapicals slender, tapering, spreading spiniferiim Kofoid and Michener.

G. Antapicals stout, incurved distally fencstmtuin Kofoid.

3. Lateral margins of epitheca with angled shoulders, antapicals spreading unequally . . scnppsi Kofoid

3. Lateral maigins of epitheca not angled, generally straight or concave 7.

7. With three antapicals, two on the left triroslre (Murray and Whitting).

7. With two antapicals . . 8.

8. Antapicals quite unequal .9.

8. Antapicals equal or subequal .10.

9. Completely reticulated, suture between 1' and 1" very oblique . . crassipes Schiller.
9. Partly reticulated, suture between 1' and 1" horizontal . , 11.

n. No spinules on distal end of antapicals dispiir sji. nov.

11. With spinules on distal end of antapicals . Iciorlnjnchiim (Murray and Whitting).

10. Antapicals not incurved distally 12.

10. Antapicals incurved distally 13.

12. Antapicals subvertical, distance between tips not over two gii-dle widths

diinydliiin Kofoid and Michener.

12. Antapicals spreading, chstance between tips over throe girdle widths rigilcnae Kofoid.

13. Antapicals tapering, slender hlackmani (Murray and W'hitting).

13. Antapicals stout, abruptly pointed ... 14.

14. Length, 118-128 ^ ■ Idndmarchii (Murray and Wliitting).

14. Length, 200-235 n. - curmtain Kofoid.

The expansum grotip
Plate 5, fig. 5-7; Plates 6, 7, 13; Plate 15, fig. 11-15

The epitheca is contracted into a distinct apical horn. Antapical horns
tend to be ecjual.

This group contains five species, H. expansum Kofoid, H. angulatum Kofoid
and Michener, H. spinijerum Kofoid and Michener, H. fenestratum Kofoid, and
H. praetextum Kofoid, all described from the collections of the Expedition.

SYSTEMATIC ACCOUNT 49

Heterodinium expansum Kofoid
Plate 5, fig. 5-7; Plate 15, fig. 11

H. expansum Kofoid, 1907a, p. 178, pi. 6, fig. 36.

Diagnosis: — A medium-sized, stout species, much flattened dorsoventrally ;
dorsoventral diameter, 0.35 transdiameter; length, 1.3 transdiameters ; apical
horn small, with rounded apex, tilted ventrally; antapical horns short, slender,
acute, widely set, straight; girdle very oblique (40°) not overhanging; surface
completely and irregularly reticulated. Length, 117 (110-130) //• Rare in the
Eastern Tropical Pacific in the Panamic Area, Peruvian Current, and South
Equatorial Drift.

Description: — This is a medium-sized species with a body almost circular in
outUne in ventral view, except for horns and girdle, and strongly flattened dorso-
ventrally, the transdiameter being about 3.0 the dorsoventral. The epitheca and
hypotheca are about equal and both apex and antapex are tilted ventrally. The
epitheca has a broadly rounded outline in the ventral view with high shoulders.
It exceeds a semicircle in ventral view and is less in dorsal. It forms 0.56 of the
total length in ventral view and 0.35 in the dorsal. It is drawn out abruptly into
a short, conical (40°) apical horn, tilted ventrally almost 40°, and nearly vertical
to the plane of the girdle. It is nearly two girdle widths long with rounded apex
and small, horizontally truncate apical pore. The ventral area is an elongated,
vertical, smooth tract, two girdle widths in length midway between girdle and
apical pore. The ventral pore is broadly reniform with the concavity facing
anterodextrally. It is located at the anterior end of the ventral area.

The broad hypotheca is a little narrower than the epitheca, with its outline
less evenly rounded. Its lateral outhne, owing to the spreading antapicals,
forms sigmoid curves. Its dorsal face is flat and the ventral concave and deeply
excavated.

The two stout, conical, finned antapical horns are wide-set, divergent not
over 18°, each about 2.0-2.5 girdle widths in length, and with acute or slightly
blunt ends. The right is a trifle stouter and a bit shorter than the left. The
postmargin between them is horizontal and almost straight with a toothed edge.

The very oblique (40°) girdle is displaced distally its own width. It is un-
usually narrow, being only 0.12 transdiameter wide on the ventral face and wider
dorsally. The precingular ridge scarcely flares from the epitheca. It lower sur-
face is angled rather than arched. The furrow is not impressed and there is only
a faint trace of rise at the postcingular margin. There is no overhang.

50 THE DINOFLAGELLATA

The sulcus is much reduced, being very narrow, and ending a girdle width
below the postcingular edge. It is vertical, straight, without lists, and has only
a slight expansion at the pore. A broad postsulcal trough is deeply excavated
below it with a postmargin 0.38 transdiameter wide.

The plates are normal. The anterior intercalary l"* lies low on the left
shoulder, its upper margin being scarcely half way to the apex. Postcingular
7' " is short, broad, and smooth. The entire surface is closely, completely, and
rather uniformly reticulate, the polygons being larger in the girdle and on the
dorsal side of the hjrpotheca. The only smooth surfaces are the ventral area,
postcingular 7' ", and, in one specimen, the intercalary zones. A secondary,
finer, more porulate mesh occurred around the periphery of the plates next to the
intercalary zone in one specimen. There are 25 polygons across the dorsal face
along the precingular rim.

In an individual observed alive, the plasma was very hyaline, and did not
fill the theca. The nucleus was ellipsoidal and centrally placed. Minute chrom-
atophores of a very pale yellowish gieen color were ii'i-egularly disti'ibuted on the
right side of the body.

Dimensions: — Length, 117 (110-130) n; transdiameter, 93 (85-100) m;
dorsoventral diameter, 27 //; antapical horns, 16 m-

Comparisons: — Heterodinium expansum finds its nearest relative in H.
angulatum; except for the flattening of the body and rounded shoulders in con-
trast to the rotundity and squarish shoulders of the latter, the two species are
somewhat alike.

The type locality is Station 4G37 in the South Equatorial Drift.

Occurrence: — Heterodinium expansum is recorded (Plate 13) at only three
of the 127 stations. There are 0, 1, 2, 0, 0 and 0 stations on the six lines of the
Expedition. Of these three stations, one (4637) is in the Panamic Area, one
(4713) in the area assigned to the Galapagos Eddy, and one (4701) in the South
Equatorial Drift. All three were in hauls from 300-0 fathoms with only a single
specimen in each haul.

The temperature at the surface ranged from 72° to 76° and averaged 73.7°.

This species is rare, eupelagic, and seemingly stenothermal in the cooler
tropical regions in deeper levels.

SYSTEMATIC ACCOUNT 51

Heterodinium angulatum Kofoid and Michener
Plate 6, fig. 1, 2; Plate 15, fig. 12
Heterodinium angulatum Kofoid & Michener, 1911, p. 284.

Diagnosis: — A small stout species; length, 1.3 transdiameters, with short
apical horn arising abruptly from the angular shoulders of the epitheca; antapical
horns equal, tapering, bluntish, incurved and ventrally deflected; postcingular
rim wholly undeveloped; surface coarsely and unevenly reticulated. Length,
85 M- Rare in the Eastern Tropical Pacific in the Easter Island Eddy.

Description: — In this robust species the body is very angular in ventral
view, elongated to a length of 1.3 transdiameters, and obese dorsally in lateral
view. The midbody is globose, scarcely compressed, but excavated midventrally,
the dorsoventral diameter being 0.9 the transverse. The antapex is tilted ven-
trally nearly 45° from the axis of the epitheca. The epitheca flares widely at the
girdle and has abruptly squared shoulders in ventral view above which it is drawn
out into a short, conical (30°) apical horn, 0.3 of its height with squarely truncate
apical pore. In lateral view it has the outline of a cone of about 80°. The alti-
tude of the epitheca is 0.7, and of the horn 0.35 transdiameter, and in lateral view
the lower part is a cone of 90° with some midventral excavation.

The hypotheca is of about the same size as the epitheca, rather less angular
dorsally; it narrows only slightly towards the antapex. Its length to the tip of
the horns is 0.8, and to the middle of the postmargin, 0.5 transdiameter.

It bears two equal, tapering, incurved, conical (25°) horns, stout, and rather
bluntly pointed, with a subsemicircular, serrated postmargin between them.
Their length is 0.25 the transdiameter and the distance between their tips is 0.55
transdiameter.

The girdle is median, very wide, with strong, overhanging precingular rim,
arched beneath. There is no trace of the postcingular ridge. Its distal end is
displaced posteriorly about 0.5 girdle width. The sulcus and ventral face are
unknown.

The plates are separated by narrow intercalary bands covered with a minute
nonporulate reticulation. The entire surface except in the part of the intercalary
zones is heavily and coarsely reticulated with a pattern of fairly regular polygons
each with a central pore across the dorsal side of the epitheca, and 15 at the post-
margin of the precingular plate. The intercalary plate 1^ had dropped out of the
wall in our specimen. It lies about midway between apex and girdle on the
dorsal face.

52 THE DINOFLAGELLATA

The plasma is coarsely vacuolated, the nucleus spherical, about 0.3 trans-
diameter across, and located at the left of the major axis at the girdle level.
Nothing else is known of the living cell.

Dimensions: — Length, 85 m; transdiameter, GO n; dorsoventral diameter,
55 n; length of antapical horns, 15 /j-

Comparisons: — Heterodinimn angulatum forms a bridge between the sub-
genera Heterodinium and Sphaerodinium. It has the globose body, little com-
pressed, of the latter, but the form of the body in a ventral view so much recalls
that of a typical Heterodinium that it is placed in that subgenus. It serves to
show that the distinction between the two groups is not a sharp one.

The type locality is Station 4691 in the Easter Island Eddy.

Occurrence: — Heterodinium angulatum is one of the rarest species of the
genus, being reported (Plate 13) only at Station 4691 in the third line in the Easter
Island Eddy in a haul from 300-0 fathoms at the surface temperature of 73° F.
It is eupelagic from the deeper levels in tropical seas.

Heterodinium spiniferum Kofoid and Michener
Plate 6, fig. 4-6; Plate 15, fig. 13
Heterodinium spiniferum Kofoid & Michener, 1911, p. 286.

Diagnosis: — A small species; length, 1.3 transdiameters, with tapering
apical horn and long, slender, spinulate antapical horns; precingular rim widely
overarching, the postcingular wholly wanting in the distal 0.25, feebly developed
elsewhere, girdle not overhanging; surface coarsely reticulate. Length, 85 m-
Rare in the Eastern Tropical Pacific in the Easter Island Eddy.

Description: — In this rather peculiar species there is a wide midbody, only
slightly compressed at the girdle, but drawn out into very long apical and antapi-
cal horns, all shghtly inclined ventrally. The total length is 1.3 transdiameters,
1.8 the dorsoventral. The epitheca is nearly a girdle width longer than the
hypotheca, and has rounded shoulders, fuller and somewhat angled on the right
side, and concave with median swelling on the left. Both dorsal and ventral
faces are concave, the latter more than the former. The epitheca is drawn out
into a tall slender horn, straight in lateral view, conical (20°) in ventral, almost
0.5 transdiameter in length, and with a truncated apex with a dorsally enlarged
lip. The ventral area is much elongated, 0.3 of the length of the epitheca, de-
flected 20° to the left, pointed at each end, and with the broadly ellipsoidal ven-
tral pore at its anterior end. The hypotheca is narrower and shorter than the
epitheca, rotund at the right, and angled ventrally and at the left. Its dorsal

SYSTEMATIC ACCOUNT 53

surface is concave and widely overhanging. At each corner is a slender, conical
(15°) horn, 0.4 transdiameter long and tapering evenly to the end in a very slen-
der, aciculate tip.

The horns are wide-set and divergent to the right, the right horn 25°, and
the left 20°. The postmargin between them is concave but very shallow, and the
serrated fin is provided with long teeth. The length of the postmargin is 0.40
and the distance between the tips of the antapicals, 0.66 transdiameter.

The girdle is submedian, tilted ventrally 10°, and displaced distally 0.5 its
width. The precingular rim is very prominent, almost horizontal, slightly arched
below, and has a narrow, hyaline, ribbed list. The postcingular rim is scarcely
developed and quite wanting in the distal quarter. The furrow is a shallow
asymmetrical trough, scarcely indented.

The sulcus is reduced to a small narrow slit, deflected distally to the left 20°,
with the flagellar pore at its anterior end about the middle of the girdle, with very
little enlargement. Its total length is only 0.16 transdiameter. The postsulcal
excavation is very wide, 2-3 girdle widths across.

The plates are not sharply outlined by differential ridges except on the dorsal
side of the hypotheca. The anterior intercalary 1^ is nearly triangular and lies
midway between the girdle and apex, mainly on the dorsal side. Postcingular
7" ' is subtriangular and lies in the side of the ventral depression.

The entire theca, including the girdle, is covered by subregular porulate
reticulations, wide-meshed in the midbody, and becoming finer towards the
apices. There are 23 polygons across the dorsal side at the precingular rim.
Secondary reticulations appear only in one dorsal suture line. The postmargin
has a narrow, serrated, ribbed list.

Dimensions: — Length, 85 n; transdiameter, 60 m; dorsoventral diameter,
50 m; antapical horns, 20 m-

Co?nparisons: — Heterodinium spiniferum has close relations with H. angu-
latuvi in the expanded girdle and in the deflection of the horns but it is much less
globose, its hypotheca being concave dorsally instead of convex as in H. angula-
tum, and it has less angulation in the shoulders. It differs from H. feneslratum
in the much finer reticulations. The antapicals are more slender than in other
species of the genus.

The type locality is Station 4695 in the Easter Island Eddy.

Occurrence: — Heterodiniurn spiniferum was taken (Plate 13) only once in a
haul from 300-0 fathoms on the fifth line at Station 4695 in the Easter Island
Eddy where the surface temperature was 74° F. Only one specimen has been
seen. It is eupelagic in tropical waters.

54 THE DINOFLAGELLATA

Heterodinium fenestratum Kofoid
Plate 7, fig. 1, 4, 5, 6; Plate 15, fig. 14
Heterodinium fenestratum Kofoid, 1907a, p. 179, pi. 8, fig. 47.

Diagnosis: — A medium-sized, symmetrical species; 1.4 transdiameters in
length, with a tapering apical horn and equal, sharply pointed antapicals with
incurved tips ; girdle overhanging ; no furrow or postcingular ridge ; surface reticu-
lations very coarse, 8 behind the girdle on the dorsal side, each polygon with
several pits. Length, 100 (80-120) fi. Rare in the Tropical Pacific in the Peru-
vian Current, the South Equatorial Drift, and the South Equatorial Current.

Description: — This is a stout, robust species of medium size, and generalized
form. The body is quite symmetrical, only slightly elongated, its length 1.4
transverse and 1.8 the dorsoventral diameters. The epitheca slightly exceeds
the hypotheca. Basally the epitheca is a low cone of 95°, symmetrical except
for a slight ventral flattening and a slight concavity on the left shoulder, the right
being straight. As a whole its dorsal side is less concave than the ventral. It is
produced into a large stout apical horn, tilted 10° to the left, conical (22°) in
shape, with slightly oblique apical pore. Its length is nearly 0.5 of the epitheca.
The ventral area appears simply as a wide part of the smooth intercalary band
between the plates at the level of the apical-precingular suture. The ventral
pore is elongate ovoidal with its axis vertical and a reniform depression at the
right. It is located 0.27 of the length of the epitheca above the girdle.

The hyptheca is almost as large as the epitheca at the girdle, almost sym-
metrical, with its right lateral margin somewhat more convex than the left. In
its distal third its sides become parallel as they pass into the stout antapicals.
Basally it is almost hemispherical, except for the relatively shallow ventral de-
pression about the sulcus.

The antapicals are stout, subconical (25°), equal, tapering horns of the same
length, about 0.20-0.25 transdiametcr in length, with sharp, incurved tooth-
like points. The postmargin between them is recessed 0.28 and the distance
between the tips is a little less than 0.5 transdiameter. The postmargin bears a
wide ribbed list.

The girdle is almost median, horizontally displaced 3 girdle widths, with an
overlap of almost twice its width. The precingular rim is very narrow and is
formed largely by a hyaline ribbed hst with sloping surface below. The post-
cingular rim is entirely lacking and the furrow is indicated only by a slight de-
pression.

SYSTEMATIC ACCOUNT 55

The sulcus is very oblique (40°) in its anterior 0.66, then turns sharply into
a vertical course, and continues to within 0.33 of the distance from the proximal
end of the girdle to the postmargin. High hyaline lists with sinuous margins
are formed on either side of it and the right one continues beyond its posterior
end. There is no clearly defined postsulcal trough but only a general depression
without definite margins.

The plates depart from the normal only in the small size of the anterior in-
tercalary which is a small equilateral triangle on the lower half of the left shoulder
mainly on the dorsal side. Postcingular 7" ' is elongated. The ventral suture of
the epitheca is vertical.

The polygons of the reticulation of the theca are exceptionally large and
unequal. They are smaller distally on the horns, in the girdle, and at the end of
the sulcus. A single row of rectangular areas of smaller size lies in the narrow
girdle. Each of the larger polygons is marked by several (3 9) small pores, in-
stead of by a single central one as in almost all other species of the genus. A few
spinules project from the angles of the mesh on the dorsal side of the apical horn.
The distal ends of the antapical horns bear a resemblance to spines.

The cell contents (Plate 7, fig. 5) were found intact in one specimen. The
cytoplasm was coarsely and uniformly vacuolated. Small homogeneous spher-
ules were scattered through the central mass of cytoplasm. A most unusual
feature was a large vacuole in the center of the epithecal region which contracted
to a conical opening at the apical pore. On its sides were small scattered rod-
lets. Another small narrow canal goes from the ventral pore up the ventral side
of the vacuole. A small spherical nucleus and a spherical chromosphere lie near
the center of the body adjacent to the flagellar pore.

Dimensiojis: — Length, 102 (80-120) m; transdiameter, 93 (85-100) m;
horns, 18 m-

Variation: — The specimens examined were remarkably uniform in form
of body and pattern of reticulations. The antapicals were more flaring and less
incurved in two individuals and the ventral depression more pronounced in one.
There is a little variation in the length of the apical and antapical horns which
is reflected in the range in length of the body (80-120 m).

Comparisons: — Like H. expansum and H. spiniferum, Heterodinium fenes-
Iratum has affinities with the subgenus Sphaerodinium in its rather stout build,
somewhat globose body, and even more in the spine-hke ends of the antapical
horns. H . fenestratum is, however, placed in the subgenus Heterodinium because
of the development of the apical and antapical horns. The incurvature of the

56 THE DINOFLAGELLATA

antapicals is like that in H. fcnestratum. The peculiar type of surface markings
with large polygons with several pores distinguishes it at once from any other
species in the genus.

The type locality is Station 4730 in the South Equatorial Drift.

Occurrence: — Heterodinium fenesiratum is recorded (Plate 13) at fifteen of
the 127 stations. There are 0, 4, 3, 3, 3, and 2 on the six lines of the Expedition
respectively. Of these fifteen stations, five (4650, 4659, 4669, 4670, 4676) are in
the Peruvian Current, nine (4679, 4681, 4705, 4709,4711, 4721, 4722, 4730,4740)
are in the South Equatorial Drift, and one (4742) is in the South Equatorial Cur-
rent. At one station only (4669) this species was taken in a surface haul and at
one station (4670) in a haul from 800-0 fathoms only. All other records are from
hauls from 300-0 fathoms.

The temperature range at these fifteen stations was 66°-81° and the average
was 72.3°. This is lower than the average for any other species of the genus.
There are but thice records above 75°, and six are below 70°.

The freciuency at all the record stations was less than 1%.

The distribution of the record stations and temperature records is sugges-
tive that H. fenesiratum is not prevalent in the warmest parts of the tropical
Pacific, but has a preference for the cooler Peruvian Current, and is carried far
to the west in the South Equatoiial Drift. It is absent from the Easter Island
Eddy, where the genus is best represented, and from the warm Mexican Current.
All record stations lie between the equator and 20° S.

It is eupelagic, stenothermal in the cooler tropical currents in the deeper
levels.

Heterodinium praetextum Kofoid
Plate 7, fig. 2, 3; Plate 15, fig. 15

Heterodinium prneUxtum Kofoid, 1907a, p. 1S4, pi. 7, fig. 41.

Diagnosis: — A very large species of irregular elongated form; length, 1.3
transdiameters, with long slender apical horn; flaring at the narrow girdle, with
impressed furrow; antapical horns stout, subequal, incurved; surface finely
reticulated, 43 polygons on the ventral face at the girdle. Length, 240 m- Rare
in the South Equatorial Drift of the Eastern Tropical Pacific.

Description: — This is the largest species known in Heterodinium. Its very
asymmetrical body is elongated and much compressed, its length being 1.3 trans-
verse and 1.7 dorsoventral diameters. The girdle is postmedian, located at 0.6
total length from the apex. The epitheca is much larger than the hypotheca.

SYSTEMATIC ACCOUNT 57

The epitheca is large and irregularly shaped, with a total altitude of 0.7 trans-
diameter. It is subconical (60° flaring basally to 90°), convex in the middle of
each shoulder, but concave on the dorsal and ventral faces and rather deeply
excavated midventrally. The right side protrudes more than the left. It is
drawn out into a long, slender, conical (20°) apical horn, inclined 10° to the right,
with a squarely truncate apex.

The ventral suture is deflected to the left and is almost right angled at the
ventral area. This area is an oblique (20°) subrectangular region, 0.2 of the height
of the epitheca above the girdle. The ventral pore is cordate with the indenta-
tion directed anterosinistrally and is located at the left end of the area.

The hypotheca is smaller than the epitheca, is subconical (55°), has less flare
at the girdle, is concave on the right and convex on the left, is dorsally very ab-
ruptly and deeply recessed, and is widely and deeply excavated ventrally.

The antapex is prolonged in two short, stout, conical (50°-60°) horns of less
than 0.2 transdiameter in length. Their tips are blunt, their ventral faces angu-
lar, and their inner faces quite concave, especially that of the left horn. The
left horn is curved ventrally. The postmargin between them is asymmetrically
concave, deepest at the right, with a reticulate hyaline fin. The depth is 0.14 and
width between tips 0.23 transdiameter, respectively.

The girdle is very narrow, 0.4-0.5 transdiameter wide, and runs almost
horizontally round the body in a sinuous course. It is displaced distally its own
width. Both precingular and postcingular rims are well developed in the proxi-
mal part, but the posterior fades away distally. The precingular is a thin hori-
zontal shelf but the postcingular a much thicker projection. The furrow is
deeply and symmetrically impressed, its depth at the left margin being half of
its width. The trough fades out dorsally.

The sulcus is a sinuous, or slightly sigmoid, narrow, deep groove, extending
0.8 of the distance from the girdle to the postmargin. It expands anteriorly
about the flagellar pore which is large, elliptical, and lies across the proximal end
of the girdle. There are no sulcal lists. The posterior end of the sulcus invades
the postsulcal area which is deeply concave and 0.28 transdiameter across at its
middle and widest part. It merges anteriorly in the general ventral excavation
of the hypotheca and is bounded laterally by the angled ventral edges of the
antapical horns.

The thecal plates are normal and clearly bordered by wide intercalary bands
except in the girdle. The anterior intercalary 1^ is a small triangular plate on the
dorsal face only a short distance above the girdle. Postcingular 7" ' is an asym-

58 THE DINOFLAGELLATA

metrical, triangular, mainly smooth plate. The thecal wall is covered with fine-
meshed, somewhat irregular reticulations, each marked by a central pore. They
are somewhat smaller distally on the horns and at the edge of the girdle. Be-
tween the plates along one side of the intercalary band, or completely filling it,
is a narrow row of minute, often rectangular, secondary polygons. There are
43 polygons along the precingular edge of the girdle. Only four polygons occur
on plate 7" '.

The cell contents were made out in the one specimen seen which was stained
in haematoxyUn. The nucleus was remarkably small for so large a cell body.
It was ellipsoidal, 0.08 transdiameter in longest diameter with the long axis sub-
vertical, centrally located, and had a faint network of chromatin threads. A
large faintly staining mass with coarser granules about 0.5 transdiameter across,
lay adjacent to the nucleus, possibly a modified chromoplast. There were two
deeply staining, rather small chromoplasts, a small vacuole filled with rodlets,
and deeply staining rounded structures adjacent to the flagellar pore (blepharo-
plasts?) and below the ventral pore. The two were connected by a deeply stained
fiber. Coarse granules in the otherwise finely granular cytoplasm were clustered
near the apical pore and along the right side. They did not blacken in osmic acid.

Dimensions: — Length, 240 n; transdiameter, 175 n; dorsoventral diameter,
130 m; antapical horns, 20 m-

Comparisons: — Heterodinium praetextum is by far the largest member of
the genus and has the best developed apical horn. In the inclination of the
apical, incurvature of the antapicals, outline of sulcus, and general form it re-
sembles H. hlackmayii, but dilTcrs from it in its narrower apical horn, stouter
antapicals, wider postmargin, and surface markings. In general shape it is more
like other members of the expansum group, especially H. fenestratum.

The type locality is Station 4740 in the South Equatorial Drift.

Occurrence: — The only record (Plate 13) of H. praetextum was in a haul from
300-0 fathoms at Station 4740 in the South Equatorial Drift on the sixth line of
the Expedition. The surface temperature there was 81° F.

It is a eupelagic tropical species.

The dispar group

Plate 5, fig. 2, 3; Plates 8, 9, 13; Plate 15, fig. 20-25

No apical horn (in ventral view); epitheca tapering uniformly; length, 0.8
transdiameter or more ; antapicals generally long and spreading.

SYSTEMATIC ACCOUNT 59

This group contains six species including H. dispar sp. nov., H. elongatum
Kofoid and Michener, H. leiorhynchum (Murray and Whitting), H. hindmarchii
(Murray and Whitting), H. curvatum Kofoid, and H. hlackmani (Murray and
Whitting) all of which occur in the collections of the Expedition.

Heterodinium dispar sp. nov.
Plate 5, fig. 2, 3; Plate 15, fig. 20

Diagnosis: — A small stout species, with globose midbody; length, 1.5 trans-
diameters; epitheca 0.82 transdiameter high; midventral suture very angled,
ventral pore large; antapicals very unequal, right sometimes hardly developed;
postmargin obliquely asymmetrical; surface sparsely porulate, sutures faint,
with a loose reticulation only on the left ventral face of the epitheca. Length,
72 (70-73) fi. Rare in Eastern Tropical Pacific in the Galapagos and Easter
Island Eddies and the South Equatorial Drift.

Description: — The midbody is globose, with only slight dorsoventral com-
pression, and divided equally by the horizontal girdle into epitheca and hypo-
theca. The epitheca is somewhat dorsoventrally compressed and slightly flat-
tened on its ventral face. The apex does not form a horn, and, seen in ventral
view, is shghtly deflected to the right with a truncate apical pore. It is sub-
conical (70-75°) in ventral view with uniformly slightly concave sides, rarely
with a slight bulge at the middle.

The hypotheca is similar in form to the epitheca, but narrower (60°), with
slightly concave lateral contour, or even shghtly convex below the girdle.

The antapex is very asymmetrical, with the antapical horns very unequal,
the left about 0.25 transdiameter long, stout, conical (20° basally contracting to
20° distally), and sometimes with a minute terminal spinule. The right horn is
very variable, sometimes scarcely developed, appearing as a blunt angle (90°), or
as a short stout cone (60°), less than a girdle width in length, or as a sharper
(20°-30°) acute cone. It is deflected to the right from 20° to 45°. The postmar-
gin is obliquely arched, scarcely indented, and measures about 0.5 transdiameter
between antapical tips.

The girdle is median on the midbody, horizontal, displaced distally its width,
with an overlap of less than 0.5 girdle width. The precingular rim forms a hori-
zontal shelf below, with an overhang of 0.5 girdle width. The postcingular rim

60 THE DINOFLAGELLATA

is marked by a low bulge in the wall. The furrow is slightly (0.2 girdle width)
impressed and widens out distally to 1.5 its proximal width.

The sulcus is 0.4 transdiameter in length, almost straight, with a single tooth
in the right margin. The postsulcal region is a broad shallow depression with
no sharp boundaries.

The greater part of the theca is marked only by a few circular pits or pores
and by the fine suture hues developed as ridges only at the postcingular rim. It
is peculiar in having reticulations developed only on part of the theca, in the few
known cases only on the left ventral face of the epitheca on plate 1", on the proxi-
mal end of the girdle, and sometimes on the antapicals and rear of the post-
margin. The plates are very faintly marked. The anterior intercalary is an
asymmetrical quadrangular plate showing on both dorsal and ventral faces,
located in the second quarter of the left shoulder. Postcingular 7" ' is nearly
equal to 1 " ' and widens out posteriorly. It is larger than in other species.

Dimensions: — Five specimens measured. Length, 72 (68-75) /x; transdiam-
eter, 51.8 (50-57) fi; length of right antapical, 3.2 (0-5) m; of left antapical, 13.8
(12-17) M.

Variation: — The size of the right antapical horn varies from about 0.2
transdiameter to a mere angled projection, in shape from a stout to a slender cone,
and in deflection from 20° to 90°. The peculiarly incomplete reticulation varies
in weight and location. Generally it is present only on the first postcingular and
in the proximal end of the girdle. One specimen only had a few polygons on the
dorsal side of the postmargin on the side of the left antapical. All specimens seen
had this restricted reticulation, so that it seems improbable that this species is
only a form of some other one which has recently undergone ecdysis.

Comparisons: — H. dispar is included in the subgenus Heterodinium on ac-
count of its flattened and excavated epitheca, but it falls between it and Sphaero-
dinium in many features.. It is near H. globosum in disproportion of antapicals
and scanty reticulation. It differs from it in absence of apical horn (in ventral
view), less globose body, lower and larger ventral pore, deeper furrow of girdle,
and less ventral deflection of antapicals. It differs from the next member in the
dispar group, H. elongahim, in its stouter form, relatively shorter epitheca, and
asymmetry of its antapicals. It is rather near H. leiorhynchum but is less glo-
bose, its apex is less curved to the left, its antapicals are much more unequal, and
lack the terminal spinules. It also lacks the doubled ribs along the lateral apical
sutures.

The type locality is Station 4683 in the South Equatorial Drift.

SYSTEMATIC ACCOUNT 61

Occurrence: — Heterodinium dispar is recorded (Plate 13) as fairly widely
distributed over the southern part of the track of the Albatross Expedition, being
found at thirteen of the 127 stations. There are 0, 0, 5, 5, 3, and 0 stations on the
six hues of the Expedition respectively. Of these thirteen stations one (4713) is
in the Galapagos Eddy, eight (4679, 4683, 4685, 4701, 4705, 4722, 4724, 4732) are
in the South Equatorial Drift, and four (4691, 4692, 4695, 4699) are in the Easter
Island Eddy. At Station 4692 it was taken in a surface haul and at the other
twelve, in hauls from 300-0 fathoms. The frequency reached the unusual level
of 1% at five stations (4683, 4685, 4692, 4695, 4701). The surface temperatures
were from 69° to 79° F., averaging 74.2°. There were only two records above
75°.

Heterodinium dispar is one of the more common species of the genus. It is
eupelagic and eurythermal, is noticeably rare at the surface, and has a predomi-
nance in the center of the South Equatorial Pacific between 5° and 25° S. It is
absent from the cold Peruvian Current, from the Panamic Area, and was not
found north of the equator.

Heterodinium elongatum Kofoid and Michener
Plate 8, fig. 1-3; Plate 15, fig. 21

Heterodinium elongatum Kofoid & Michener, 1911, p. 284.

Diagnosis: — A small species with symmetrical conical epitheca 0.9 trans-
diameter high ; midventral suture sUghtly arched ; apical region not curved ; ant-
apicals equal, conical, not curved; sutures lightly ribbed; reticulation complete,
10 polygons from girdle to apex. Length, 62-80 ii. South Equatorial Drift
and Equatorial Counter Current of the Eastern Tropical Pacific.

Description: — A small, slender, erect, rather symmetrical species with
elongated body whose length is 1.6 transdiameters. The epitheca is about equal
to the hjrpotheca and girdle together. The dorsoventral diameter is almost
exactly equal to the transverse at the precingular ridge. The epitheca is 0.9
transdiameter in height, conical (60°) in ventral view, with slightly convex sides.
The ventral face is nearly flat, with a median ventral depression, its slope ven-
trally deflected 28° from the vertical axis, and its dorsal side flaring in the proxi-
mal 0.66 in dorsal view, with an almost hemispherical bulge to the precingular
rim. This sets off dorsally an apical horn in lateral view only, of conical (35°)
outline, dilated dorsally, with an obliquely truncated apical pore sloping down

62 THE DINOFLAGELLATA

dextrodorsally. The midventral suture arches to the left. The ventral area is
a subtriangular region to the left of the suture midway between girdle and apex.
The ventral pore has a broadly reniform outline with the indentation facing the
right.

The hypotheca is shorter than the epitheca, 0.66 transdiameter in extreme
length, slightly angular at the sutures, but subhemisphei'ical aside from the ant-
apical horns. It is more convex dorsally than ventrally and the horns lie nearer
the ventral than the dorsal side. It is rather deeply excavated ventrally with
angular borders about the depression.

The antapical horns are equal, though in some specimens the left is a very
little smaller than the right. Both are symmetrically conical (25°), spreading
10° from the vertical, pointed, and without spine or fins, though ridges of the
surface reticulation run to the tip on some specimens. The indentation of the
postmargin between them is symmetrical, its depth is 0.15, and the distance be-
tween the tips of the antapicals is 0.40 transdiameter. A hyaline toothed fin
borders the central part of the arched postmargin.

The girdle is relatively very wide, 0.17 transdiameter across, nearly the same
width throughout, except at the extreme distal end where it flares abruptly and
is displaced posteriorly its own width. There is scarcely any overlap. The
precingular ridge is somewhat more protuberant than the postcingular. It does
not flare, or flares but little, is arched below, and runs a smooth even course. The
postcingular ridge is indented posteriorly at the proximal end for a short distance
and becomes increasingly deficient in the distal quarter where it curves rapidly
posteriorly. It is formed by a blunt angle of the body wall. The furrow is
impressed throughout, more deeply in the proximal end, and becoming shallower
distally. Its depth is about 0.5 girdle width and the trough is asymmetrically
deeper anteriorly.

The sulcus is almost straight and vertical, 0.4 transdiameter in length, nar-
rowly contracted near the middle, and expanded in the furrow into the rectangu-
lar flagellar pore. There are no sulcal lists. A deep, trough-like postsulcal area
lies behind the sulcus, bordered by angular elevations on the ventral faces of the
antapicals.

The thecal wall is reticulate throughout, including the girdle, but, excepting
postcingular plate 7" ', is entirely smooth. The polygons in the girdle which are
reticulate throughout, are arranged in two rows, the lower quadrangular or pen-
tagonal, the upper smaller and somewhat hidden in the arching precingular list.
The polygons elsewhere are quite large and subuniform in size, except towards

SYSTEMATIC ACCOUNT 63

the apex where they decrease in size. They tend to be rectangular and there are
only two or three rows in the plates adjacent to the girdle. Each polygon bears
a single central pore. Secondary reticulations were seen only on the dorsal post-
cingular ridge in the specimen figured (Plate 8, fig. 1-3). On another specimen
they were numerous along all the main sutures. There are 19 polygons along
the precingular ridge and 8-10 from the girdle to the apex on the dorsal face.
The sutures between the plates are clearly mai-ked by ridges heavier than the
reticular mesh. The anterior intercalary is an irregular quadrilateral midway
on the left shoulder. Postcingular 7" ' is two girdle widths in length, widest
(nearly a girdle width) in its posterior third, and devoid of mesh or pores.

The cell contents were observed only in a single specimen. The cytoplasm
was rounded up in a spherical mass filUng the midbody. Near the center was a
spherical nucleus, a girdle width in diameter, adjacent to a spheroidal chromo-
sphere.

Dimensions.- — Length, 73.6 (62-80 n); transdiameter, 48.2 (40-57) m; dor-
soventral diameter, 35.5 m; right antapical horn, 10.6 (7-12) n; left antapical
horn, 11 (8-13) n.

Variation: — The epitheca varies in lateral contour from nearly straight to
slightly convex with some precingular flare. There is also some variation in the
degree of angularity of the hypotheca. The specimen figured (Plate 8, fig. 1-3)
is near the extreme in this feature. The apical pore varies from transverse
to oblique and the antapicals range from 25° to 40° in their conical contour.
They are quite constantly nearly equal in contour, length, and deflection from
the vertical, differing in this respect from H. scrippsi, in which their inequality in
these three features is considerable. There is also some variation in the fre-
quency of the secondary polygons along suture lines correlated with the develop-
ment of the intercalary zones.

Comparisons: — Heterodinium elongatum lies between H. leiorhynchum and
H. hindmarchii in the^ dispar group. It differs from the former in the much
greater development of reticulations, the greater equality of the antapicals, lack
of curvature in the apical region, and in the absence of terminal spinules on the
antapicals. It differs from the latter in the shorter straight antapicals, as com-
pared with the longer arched ones of H. hindmarchii. The sulcus in the latter
species is short and wide, in the former very narrow. The epitheca is also stouter
and the reticulations heavier and more uniform in H. hindmarchii. There is
considerable resemblance between H. elongatum and H. scrippsi of the crassipes
group. H. scrippsi has unequal, more divergent antapicals, more expanded and

64 THE DINOFLAGELLATA

angled shoulders on the epitheca, and 15 instead of 10 polygons between apex
and girdle on the dorsal side; in other words, the polygons are relatively more
numerous. H. scrippsi is also larger, 140-155 n (in Expedition collections 115 m)
as compared with 62-80 m-

The type locality is Station 4724 in the South Equatorial Drift.

Occurrence: — Heterodiniuni elongalum occurred (Plate 13) at seven of the
127 record stations. There are 0, 0, 2, 1, 3, and 1 stations respectively on the six
lines of the Expedition. Of these seven stations, six (4079, 4681, 4701, 4724,
4732, 4734) are in the South Equatorial Drift, and one (4742) in the Equatorial
Counter Current. The species was not taken in any surface haul, six being from
300-0 fathoms and one (4681) from 800-0 fathoms.

The temperature range at the seven stations at the surface was 68°-81° and
the average 75°.

The frequency at all stations was less than 1%.

This species is eupelagic, and tends to be stenothermal at the higher tempera-
tures of the tropical Pacific. The records are confined to well-established tropical
conditions and there is an avoidance of the surface levels. It is absent from the
Peruvian Current and the Panamic Region.

Heterodinium leiorhynchum (Murray and Whitting)
Plate 15, fig. 22

Peridinium leiorhynchum Murray & Whitting, 1899, p. 326 327, pi. 29, fig. 2a, b.
Heterodinium leiorhynchum Kofoid, 1906a, p. 358; Entz, Jr., 1909, p. 246.

Diagnosis: — A medium-sized species with very globose midbody; epitheca
0.75 transdiameter high; midventral suture slightly angled, ventral pore small;
apex curved to right, lateral apical sutures with double ribs; antapicals slightly
unequal, the right 0.50-0.66 length of the left ; sutures ribbed ; reticulations sparse,
restricted to left ventral face of the epitheca and proximal girdle. Length, 95 fx.
Eastern Tropical Pacific, Atlantic Ocean, and Mediterranean Sea.

Description: — This is a medium-sized, stout, rotund species, with a total
length of 1.55 transdiameters. The epitheca and hypotheca are subequal, and
the apical and antapical horns are vertical in lateral view. The epitheca in ven-
tral view is almost an equilateral triangle, subconical (55°-60°), flaring a bit at
the girdle, with the left margin concave, and the right slightly convex in the
middle. In lateral view the epitheca shows a sharp distinction between the
globose midbody and a distinct apical horn which is entirely obscured in the ven-

SYSTEMATIC ACCOUNT 65

tral view. The epitheca is somewhat flattened dorsoventrally, its diameter in
that axis at the girdle being 0.82 transdiameter. The midbody in this view is
subconical (90°) with shght dorsal tilt and forms 0.5 the total altitude of the
epitheca. The apical horn is conical (20°), 0.5 the total epitheca in height, and
with a truncate apex, hpped where the lateral ridges end. In ventral view it is
noticeably curved to the right. The midventral suture is only slightly deflected.
The ventral pore is 0.33 of the length of the epitheca above the girdle. It is
small and circular in outline.

The hypotheca is basally hemispherical, excavated midventrally, and termi-
nates in two prominent antapical horns. They are unequal, the left being 1.5
the length of the right. Both are conical, the right 25°, the left 30°, and each
bears an acute terminal spinule about 0.25 its length in length. They diverge un-
equally, the right about 10° and the left about 20° from the vertical. The post-
margin between them is deeply and asynmietrically arched, being deeper at the
right. Its depth is 0.33, and the distance between the tips is 0.56 transdiameter.

The girdle is median in location, tilted a trifle ventrally, displaced posteriorly
at its distal end one girdle width, and without overlap. The girdle is unusual
in this species in that it grows narrower instead of wider distally, being about half
as wide in the distal quarter as in the adjacent proximal quarter. The precingu-
lar and posticingular rims are subequal, the latter being deficient dorsally. Both
are very low ridges. The furrow between them is flat.

The sulcus is short, barely two girdle widths in length, rather sharply angled,
with spinous fin on the right margin. The postsulcal area is not sharply limited
and is very short, scarcely a girdle width in length.

The thecal wall is sparsely porulate and is reticulated only on the ventral
face over precingular plate 1" and in the proximal quarter of the girdle. Small
secondary polygons follow the suture between precingulars 5" and 6" and in the
postcingular rim. There are only six polygons at the precingular rim. The
polygons in the girdle consist of a single large posterior row and above them a row
of more numerous smaller ones. The suture fines are generally heavily ribbed,
the lateral apicals bearing parallel double ribs. The plates are clearly outfined,
except in the girdle. The anterior intercalary, 1^, lies on the dorsal side midway
between the girdle and apex. Postcingular 7" ' is very wide and short.

Nothing is known of the cell contents.

Dimensions: — Length, 95 ix; transdiameter, 62 /i; dorsoventral diameter,
50 yu; length of right antapical, 16 m, of the left, 25 m- Five specimens were
measured.

66 THE DINOFLAGELLATA

Variation: — Our single specimen has a somewhat more tapering (45°)
epitheca than in Murray and Whitting's figure (their pi. 29, fig. 2a), has a shorter
light antapical (0.5 the length of the left), and has reticulations on the tip of the
left antapical.

Comparisons: — Helerodinium Ieiorhynchu7n differs from all other members
of the dispar group in having well differentiated spinules on the tips of the antapi-
cals. Its apical horn, in lateral view, is similar to that of H. blackmani, but
shorter. Its antapical horns are more unequal than in any other species of the
group except H. dispar and are more divergent than in H. elongatum. Its reticu-
lations are restricted in the same general manner as in H. dispar and are much
coarser than in H. blackmani, H. curvatum, H. elongatum, and H. hindmarchii.

Synonymy: — This species was described by Murray and Whitting (1899) as
Peridinium leiorJnjnchum and transferred to Heterodinium by Kofoid (1906a).

The type locality is 20°-40° N., 30°-50° W. in the warm temperate Atlantic
(Murray and "Whitting, 1899).

Occurrence: — Heterodinium leiorhynchum occurred (Plate 13) at only a
single station (4697) on the fourth Une of the Expedition in the Easter Island
Eddy in a haul from 300-0 fathoms at a surface temperature of 75°.

This species was first reported at two stations by Murray and Whitting
(1899) from the warmer temperate and tropical Atlantic from 20° to 40° N. and
30° to 50° W. in March-April at surface temperatures of 60°-76°. Entz, Jr.
(1907, 1909) recorded it at Naples in November.

Heterodinium hindmarchii (Murray and Whitting)
Plate 8, figs. 5, 7; Plate 15, fig. 23

Peridinium HindmaTchii Murray & Whitting, 1899, p. 326, pi. 29, fig. la, b.
Heterodinium hindmarchi Kofoid, 1906, p. 359.

Diagnosis: — A medium-sized, rather elongated species, with tapering,
shghtly inclined epitheca; total length, 2.0 transdiameters ; antapicals 0.6 trans-
diameter long, widely separated, asymmetrically divergent and incurved; surface
completely reticulated with uniform or unlike polygons. Length, 124.2 (118.0-
128.0) fi. Rare in the tropical Atlantic and also in the Pacific in the Mexican
Current, South Equatorial Drift, and Easter Island Eddy.

Description: — This is a medium-sized species of robust habit. The body
is elongated to a total length of 2.0 transdiameters, chiefly because of the exten-
sion of the epitheca which is evenly drawn out towards the squarely truncated

SYSTEMATIC ACCOUNT 67

apex. The epitheca equals the hypotheca and the girdle. Its extreme ventral
altitude is 1.07 transdiameters. It is conical (45°) with almost symmetrically
concave sides, flaring only a little towards the girdle, the left a little more concave
than the right, and is flattened on the ventral face. The ventral area is broadly
subtriangular, with a centrally located, subcircular ventral pore with a reniform
indentation facing horizontally to the right.

The hypotheca is subhemispherical measured from the postcingular level
and excluding the antapicals. It is, relatively to the hypotheca, short and broad,
with a short concave right and a longer convex left lateral margin and a shallow
ventral depression.

The antapical horns are subconical (right 12°, left 20°), long and slender,
usually bluntly pointed, but in some individuals with an abrupt acute tip. They
are usually incurved, the shorter right horn more than the longer left. The right
is about 0.4, the left 0.4 transdiameter long. The postmargin is deeply arched
and the indentation asymmetrically inclined to the right. The horns diverge un-
equally, the right 15°, the left 27° from the vertical. The depth of the excava-
tion is 0.37 and the distance between the tips of the antapicals 0.86 trans-
diameter.

The girdle is ahnost median in the midbody, but one girdle width postmedian
in the body as a whole. It is subhorizontal, tilted a bit dextroventrally and dis-
placed distally its width, and is without overlap. The precingular margin steeply
overhangs, is arched below, and forms a smooth regular curve. The postcingular
rim is wanting or, at the most, is represented by a trace of a local bulge in the
proximal part only. The furrow is not impressed.

The sulcus is short, 0.24 transdiameter in length, very narrow, almost
straight, and without lists. The postsulcal area is set off by a low elevation on
either side. Its width is twice its height and no hst was seen on the postmargin.

The thecal wall including the girdle, but excluding postcingular plate 7" ', is
entirely and rather uniformly reticulated, with subregular porulate polygons.
There are 12 polygons between the apex and the girdle and 13-15 at the precingu-
lar rim on the dorsal face. The sutures between the plates are obscured by the
mesh. The anterior intercalary plate 1* is asymmetrically quadrangular, almost
triangular, and lies below the middle of the left shoulder on the dorsal side.
Postcingular 7" ' is nearly eciual to 1" ', is broader than usual, and is not always
reticulated.

The cell contents were found intact in one individual of forma maculata.
The finely granular plasma filled the theca. The small, ellipsoidal nucleus is

68 THE DINOFLAGELLATA

centrally located just below the girdle and is a girdle width in long diameter.
Adjacent to it is a slightly larger, spherical, greenish yellow chromosphere, al-
most surrounded by a vacuole and two girdle widths in diameter. Several small,
spherical, dark greenish chromoplasts lie along the periphery at the girdle level.

Dimensions: — Length, 124.2 (118-128) m; transdiameter, 61.8 (62-65) m;
right antapical, 30 (25-33) m; left antapical horn, 33.8 (32-39) m- Murray and
Whitting's specimen is larger and measures: length, 137 m; transdiameter, 67 n;
antapical horns, 35 and 40 m, respectively.

Variation: — This is most obvious in the degree of elongation of the body,
the specimen figured by Murray and Whitting (1899) being longer than those
from the Pacific. There is a fair range of vaiiation in the length, curvature, and
deflection of the antapical horns.

Status of Heterodinium hindmarchii forma maculatum Kofoid: — In the first
preliminary account of the dinoflagellates of the Expedition, Kofoid (1907a)
described as forma maculata the specimen here figured (Plate 8, fig. 5, 7). It
was distinguished by reason of the very characteristic surface reticulations.
These differ notably from those on Murray and Whitting's (1899, pi. 29,
fig. la, lb) specimen in number, pattern, and especially in uniformity. The
eight other specimens in the collections of the Expedition all conform in these
characters to the type as figured by Murray and Whitting.

The evidence in the genus as a whole leads us to regard secondary reticula-
tions which appear along the intercalary zones on the edges of the primary reticu-
lations as phenomena related to the increase in size prior to ecdysis. The widen-
ing of the intercalary zones between the plates is followed or accompanied by the
spread of smaller, non-porulate, often rectangular reticulations along the sides,
or even completely filling these zones.

The specimen designated as forma maculata conforms to these specifications
in that it has intercalary zones, and small rectangular polygons bordering these
zones, in the usual fashion. It has, however, one additional feature which in
om- present knowledge of the process of growth preceding ecdysis and division,
is diflSicult to explain as a part of that process and is also without parallel else-
where in the data from this genus.

This disturbing feature is the presence in forma maculatum of small non-
porulate polygons not only along the suture lines but also in a somewhat regulated
manner between polygons within the plates, as for example in the dorsal pre- and
postcingular plates (Plate 8, fig. 5, 7) in the three apicals, in the upper part of the
girdle, and seemingly over the entire surface of the antapical horns.

SYSTEMATIC ACCOUNT 69

The plates of the theca of Heterodinium are separable structural units,
parted by sutures. The intercalary zone seems to be formed by expansions of
these units by the addition of growth-regulated zones on their periphery. On this
basis the appearance of secondary polygons on these expanding zones as they
emerge is understandable, but their emergence as the result of growth between the
old polygons is difficult to postulate, especially as there is no evidence elsewhere
within the Dinoflagellata of such a degree of separability or unitary regulation of
polygons as this h^-pothesis demands.

Comparisons: — Heterodinium hindmarchii is the smallest of the four large
species which terminate the H. dispar group, the other three being, H. trirostre,
H. curvatum, and H. hlackmani. It lacks the ventral subsidiary, left antapical of
H. trirostre, has relatively stouter antapicals than any of them, less development, .
less curvature of the apical than either H. curvatum or H. hlackmani, and has
much more developed, more divergent antapicals than H. dispar, H. leiorhynchum,
or H. elongatum.

The excessive rotundity of this specimen, the wide intercalary zones,
and the marginal secondary polygons along sutures, all support indubitably
the conclusion that this specimen is approaching ecdysis. That the large
number of small secondary polygons distributed within the various plates which,
in part, give the thecal wall of this specimen its unusual appearance, is also
merely a part of the preparatory process and not a genetically differentiat-
ing structure, is at least questionable, and certainly puzzling. We therefore
retain the designation forma maculatum to draw attention to the need of more
evidence on the process of ecdysis and especially on the extent of the regulative
changes which attend this and other modifications of the dinoflagellate thecal
wall.

Heterodinium hindmarchii forma maculatum is represented in the collections of
the Expedition by two specimens, taken with the tjqaical form of the species, at
Stations 4691 and 4699 on the third and fourth lines of the Expedition in the
Easter Island Eddy in hauls from 300-0 fathoms where the temperatures at the
surface were 73° and 75° respectively.

Synonymy: — Originally described as Peridinium Hindmarchii by Murray
and Whitting (1899), this species was transferred to Heterodinium by Kofoid
(1906a). The forma maculatum described by Kofoid (1907a) may be an old in-
dividual in which intercalary growth is taking place along with secondary reticu-
lation of the theca, especially in the intercalary zones.

The type locality is 34° N., 39° W. southwest of the Azores in the Atlantic.

70 THE DINOFLAGELLATA

Occurrence: — Heierodinium hindmarchii is one of the more common species
of the genus. It is recorded (Plate 13) at ten of the 127 record stations. There
are 2, 0, 1, 4, 3, and 0 respectively on the six lines of the Expedition. Of these ten
stations, two (4605, 4609) are in the Mexican Current, four (4701, 4719, 4724,
4737) in the South Equatorial Drift, and four (4691, 469.5, 4697, 4699) in the
Easter Island Eddy. There is a center of occurrences (5 stations) to the north
of Easter Island but the remaining records are widely separated. All are from
hauls from 300-0 fathoms, except one (4737) from a vertical haul from 100-0
fathoms. The temperature range at these ten stations was 72°-85° and the aver-
age was the rather high figure of 77.1° F.

The frequency was always less than 1%.

It also occurs in the tropical Atlantic. Murray and Whitting (1899) re-
port it from eleven stations from about 34° N, 39° W, to Panama from July to
December at surface temperatures of 60°-81°, but never in abundance.

This species is very evidently both eupelagic and eurythermal, but is con-
fined to lower levels in the collections of the Expedition, at least. It has a wide
distribution but is infrequent. Its centers of occurrence are clearly in the warm-
est parts of the tropical seas.

Heterodinium curvatum Kofoid
Plate 8, fig. 4, 6; Plate 9, fig. 5, 6, 8; Plate 15, fig. 24; Plate 17, fig. 41

Heierodinium curvahim Kofoid, 1907a, pp. 1<)4, 179, pi. 8, fig. 48.

Pcrulinium pukhrum Hensen, 1911, p. 174, fig. C 8, Tab. XVI, non Tab. XVII (= Pcrvtiiiiiwi " jioro-
sum").

Diagnosis: — A large, elongated, slender species; total length, 1.8 trans-
diameters; epitheca very slender distally, apex much curved to the right and
dorsally; postcingular ridge developed throughout; sulcus stops 0.66 of the dis-
tance from girdle to postmargin; antapicals stout, both incurved distally, tips
bluntish; surface reticulated throughout with small subuniform polygons which
along the apical sutures are rectangular, not horizontally elongated. Length,
218 (200-235) m- Eastern Tropical Pacific in the Mexican Current, Easter
Island Eddy, and the Equatorial Drift and Atlantic.

Description: — This is a large, much elongated, asymmetrical species of
slender habit, its length 1.67-1.75 transdiameters, and its dorsoventral diameter
0.78 the transdiameter. The epitheca and hj'potheca are equal in length in the

SYSTEMATIC ACCOUNT 71

middorsal region but in ventral view the hypotheca is 0.8 the length of the epi-
theca. The epitheca in ventral view is subconical (45° basally, decreasing to
30° distally), with a straight left margin and concave right, especially towards the
apex, due to the dextral curvature (20°) of the apical horn. In ventral view this
horn is not differentiated by constriction as it is in the lateral views. There is
some flare at the girdle, convex at the right, concave at the left. In lateral view '
the apical horn is set off by an abrupt change in flare at about 0.33 of the distance
from girdle to apex, below which the epitheca is a cone of 90°, and above of 20°,
but with marked dorsal curvature and an obliquely truncate apex sloping dex-
trodorsally. The dorsal side is a symmetrical concave cui-ve, the ventral convex
in the upper 0.66, straight in the lower 0.33, and depressed in the midventral
region.

The hypothecTa basally is asymmetrically subconical, 55° in ventral view, and
70° in lateral, somewhat angular on the dorsal face and concave with deep, ven-
tral sulcal excavation.

The antapical horns are subequal, the right a bit longer than the left, and
approximately 0.5 transdiameter in length. They are subconical, distally about
20° but increasing basally, the right to 30°, the left to 45°. Each has a prominent
midventral ridge. They are incurved in their distal 0.33, the left more than the
right, with bluntish tips, the left sharper than the right. In lateral view the
median ridge on the ventral surface gives the appearance of a secondary point
near the tip. The postmargin is arched, asymmetrically concave, and deepest
at the right. The distance between the tips is 0.62 and the depth of the excava-
tion 0.43 transdiameter. The postmargin bears a low, dentate, hyaline list
over most of its edge.

The girdle is postmedian, tilted 20° ventrally from the horizontal, displaced
distally scarcely its own width, with no overlap, and a sUghtly sinuous course on
the dorsal face. It is of uniform width throughout and its postcingular ridge is
almost as well developed as its precingular one. The girdle is nearly uniform in
width throughout. Its two ridges are heavy triangular projections and the fur-
row between them is almost symmetrically impressed, being only a trifle deeper
posteriorly. There is scarcely any fading out of the postcingular rim in this
species, a feature so widely prevalent in most other species of the genus. The
girdle is also rather narrow, being only 0.07 transdiameter across.

The sulcus is 0.33 transdiameter in length, very narrow, except where it ex-
pands anteriorly into the flagellar pore at the proximal end of the girdle. It is
deflected to the left and is slightly sinuous. There are no lists. There is a very

72 THE DINOFLAGELLATA

wide and short (1.3 girdle widths) postsulcal trough between the ventral ridges
on the antapicals.

The plates are clearly defined by either ridges or narrow intercalary zones.
Each lateral apical suture bears a low hyaline fin. The mid ventral suture is
gently curved, concave to the right, and the ventral area not clearly defined at
its junction with the apical-precingular horizontal suture. The ventral pore is
elongated reniform with the concavity obliquely facing the right. The anterior
intercalary is an asymmetrical quadrilateral plate with sinisti-odorsal exposure
just below the middle of the left margin forming the second quarter of the length
of that margin. Postcingular 7" ' is of a pecuUar shape, somewhat hke a broad
paddle with the narrow handle in the distal end of the girdle. It is unusually
wide (2 girdle widths) and squarish posteriorly. It is the only plate, outside of
the girdle, which is not reticulated.

The surface of this species is heavily reticulated with subuniform, rather
small, porulate polygons. They are often rectangular along sutvu-e lines but are
not elongated as in H. blackmani. They fade out at the apex and tips of the
antapicals, are wholly lacking on postcingular 7" ', on the left ventral face below
postcingular plate 1" ', and in the posterior half only of the furrow. Two rows
of small polygons lie in the upper half of the furrow. Very minute, secondary,
non-porulate reticulations were seen along the sutures in one specimen in this
species, probably approaching ecdysis, as its intercalary bands were well de-
veloped. There are about thirty-five polygons at the girdle along the precingular
ridge and twenty-four from girdle to apex along the midventral suture.

The cell contents are unknown lieyond the observation of a yellowish brown
chromosphere in one individual.

Di7nensions: — Length, 218 (200-235) n; transdiameter, 130 m; dorsoven-
tral diameter, 110 m; I'ight antapical, 58 m; left antapical, 54 m-

Variation: — Our material was quite uniform, with reticulate surface,
and marked curvature of the horns. One specimen from Station 4587 had
wide intercalary zones, maximum size (235 n), secondary polygons along
sutures, and a stouter but more curved apical horn. It was probably approach-
ing ecdysis.

Comparisons: — Helerodinium curvatum is very close to H. blackmani in size,
general shape, pattern of antapicals, and curvature of the apical. //. curvatum
has a more slender apical region, stouter and blunter antapicals, and its sulcus
runs only 0.66 posteriorly from the girdle towards the postmargin, while in H.
blackmani it runs all the way. The most striking difference is in the extent and

SYSTEMATIC ACCOUNT 73

pattern of the reticulations. The reticulations cover the entire surface, with the
very small exceptions noted above, in H. curvatum, but tend to be either wholly
lacking, or feebly developed, in the pre- and postcingular plates, except 1", in
H. blackmani. Postcingular plate 7" ' in H. curvatum is very broad and paddle-
shaped, while in H. blackmani it does not narrow into the handle-shaped projec-
tion in the girdle region and is not so broad posteriorly. For these several reasons
we do not regard H. curvatum as an H. blackmani with more completely developed
surface reticulations. Such development could scarcely bring about such con-
siderable changes in the pattern of the polygons, the shape of postcingular 7" ',
and the sulcus. Murray and Whitting's (1899, pi. 29, fig. 2a, 2b) figures of this
species present certain anomalies in structure which our figure (Plate 9, fig. 4)
clarifies. They have drawn the ventral face of the epitheca without any ventral
suture, ventral area, or ventral pore. The pattern of reticulation, both as to
number and shape of the polygons, is suspiciously similar to that which they figure
for the dorsal surface. We conclude that they focused on the dorsal surface and
drew it in their figure as though it were the ventral. In any event their figure is
anomalous and incorrect in the matter of reticulations on the ventral face of the
epitheca.

Synonymy: — Hensen (1911, p. 174, fig. C 8) published as Peridinium pul-
chrum an inverted and very imperfect figure of Heterodinium which is probably
this species, though he figures no sulcus and the reticulations are diagrammati-
cally drawn with certain regions blank. The reticulations are so placed in his
sketch that one is led to infer that the blank areas were also reticulated, at least
they do not correspond in location to the usual blank. Because of the small size
of the polygons, complete reticulation, and the very tapering epitheca, we ten-
tatively place this form of Hensen's in H. curvatum. Its extensive distribution in
the Atlantic is comparable with that found in the collections of the Expedition
from the Pacific.

The type locality is Station 4699 in the Easter Island Eddy.

Occurrence: — Heterodinium curvatum is recorded (Plate 13 and Plate 17,
fig. 41) at seventeen of the 127 stations. There are 4, 0, 6, 6, 1, and 0 stations re-
spectively on the six fines of the Expedition. Of these seventeen stations, four
(4583, 4587, 4590, 4594) are in the Mexican Current, seven (4679, 4680, 4687,
4688, 4701, 4705, 4739) are in the South Equatorial Drift, and six (4691, 4692,
4697, 4698, 4699, 4700) are in the Easter Island Eddy. At six stations (4590,
4680, 4688, 4692, 4698, 4700) the species was taken in surface hauls. The other
eleven records are from 300-0 fathoms. The temperature range at the seventeen

74 THE DINOFLAGELLATA

stations at the surface was 68°-84° and the average was 75.4°. Ten of the
seventeen records are at temperatures of 72°-75°.

The frequency was 3% at Station 4692 and 2% at 4698, both surface hauls,
and 1% at 4700. The frequency at the other fourteen stations is less than 1%.

Hensen (1911) reports this species as Peridinium pulchrum at twenty stations
in the tropical Atlantic distributed as follows : five in the Eastern and four in the
Western South Equatorial Current, two off the coast of Brazil, four in the Guinea
Current, one in the South Equatorial Current, one in the Sargasso Sea (1 speci-
men), three in the Gulf Stream, and one in the North Sea. The computed num-
ber taken was 317 and the greatest abundance was recorded in the Western South
Equatorial and Guinea Currents. It is quite probable that records for H. black-
mani are included with his for this species.

This species is eupelagic, eurythermal, and has a wide distribution. It has
a marked center both of occurrences and frequency in and near the Easter Island
Eddy and another small group in the warm Mexican Current. The scattered
records in the South Equatorial Drift are in waters to which the Easter Island
Eddy is to some extent tributary. The most striking feature of the occurrence
of this species is its relative frequency in surface collections. The records of 3%
at Station 4692 and 2% at 4698 are not equalled by any other species in the genus
Heterodinium. There are in all six records in the total of seventeen, from surface
hauls. There are, however, only seventeen records in all from surface hauls for
all species of the genus. Therefore this species, more than any other in the
genus, shows an abihty to thrive in surface waters. There are only two species
in the genus which exceed it in number of occurrences, namely H. rigdenae with
twenty-three and H. milneri with nineteen. It is one of the dominant species
of the genus.

Heterodinium blackmani (Murray and Whitting)
Plate 9, fig. 1-4, 7; Plate 15, fig. 25

Peridinium Blacktimrd Muhray & Whitting, 1899, p. 327-328, pi. 29, fig. 6a, b, c.

Heterodinium blackmani Kofoid, 1906a, p. 358; Karsten, 1907, p. 238, 243, 244, 274, pi. 47, fig. 6ii, b.

Diagnosis: — A very large, stout, handsome species; length, 1.7 transdiam-
eters; epitheca 1.0 transdiameter high, an asymmetrical cone of 50° curved dex-
trally, flaring at the girdle; postcingular ridge equally developed throughout;
sulcus extending to the postmargin; antapical horns slender, subecjual, the left in-
curved; surf ace coarsely, irregularly, and partially reticulated, polygons along the

SYSTEMATIC ACCOUNT 75

sutures between apicals horizontally elongated. Length, 230 (220-270) m.
Rare in tropical seas, Atlantic, Indian, and Eastern Tropical Pacific in the Mexi-
can Current, Easter Island Eddy, and South Equatorial Drift.

Description: — This is next to the largest and one of the most striking mem-
bers of the genus. The body is much elongated, about 1.7 transdiameters in
length, much expanded at the girdle, with a somewhat globose midbody, but
flattened dorsoventrally distally. In ventral view it has a stout habit. The
length of the epitheca at the niidlateral girdle is 1.25 that of the hypotheca. In
ventral view, the epitheca is asymmetrically subconical, 65° basally, narrowing to
40° distally. The right side is symmetrically concave, the left nearly straight,
except towards the apex which is deflected about 25° dextrally. There is scarcely
any increase in flare at the girdle. There is no differentiated apical horn in the
ventral view, but in the lateral, the midbody abruptly contracts at the level of the
apical-precingular sutures into a slender symmetrical zone (17°), deflected dor-
sally 7° from the perpendicular to the plane of the girdle. The apex contracts at
the obUque apical pore. The ventral suture is straight, angled at the apical-
precingular suture. The ventral area is not marked off by any special markings.
It lies at the junction of the midventral suture and the apical-precingular one.
The ventral pore is small, ellipsoidal, reniform, with an indentation on the right
side. In one case it was possible to detach the ventral plate as a distinct platelet
of irregular quadrangular shape with the reniform ventral pore in its center
(Plate 9, fig. 7). The midbody in lateral view is asymmetrically subglobose, ex-
cavated midventrally, with the longer slant on the anterior ventral and posterior
dorsal faces.

The hypotheca is about equal to the epitheca on the dorsal face, and is 0.66
its length ventrally. Basally in ventral view it is a cone of about 65° with con-
cave sides spreading distally in the two antapicals. The ventral face is deeply
excavated.

The antapical horns are conical, the right 30°, the left 25°, sharp-pointed, the
right straight, deflected dextrally 25° from the vertical, the left deflected sinis-
trally and sharply incurved in its distal third. Both are sUghtly deflected ven-
trally and are ribbed down the midventral surface. The postmargin is asym-
metrically curved, deflected to the right with more of a tendency towards an
angular outUne than in related species. The postmargin bears a narrow, hyahne,
minutely serrated, sometimes faintly reticulated fin. The distance between tips
is 0.61 and the depth of the indentation is 0.40 transdiameter.

The girdle is narrow, 0.045 transdiameter wide, runs a smooth course, is dis-

76 THE DINOFLAGELLATA

placed posteriorly its own width at its distal end, and has no overlap. The pre-
and postcingular ridges are low and stout, without lists, and the latter is only a
trifle less developed than the former, even to its distal end. The furrow is sym-
metrically impressed into the wall about 0.5 its width. The plane of the girdle is
tilted ventroposteriorly not over 15° from the vertical axis.

The sulcus has the unusual form in this species of an asymmetrical channel
extending from the large flagellar pore in the proximal end of the girdle, the whole
distance to the postmargin. It widens out and bends to the left below the girdle
to nearly a girdle width, and, beyond this, is a straight narrow channel in its
distal third. A heavy rib borders it on the left anteriorly and a high hyaline
list overhangs the right side.

The plates are marked off by very prominent ribs or hsts. The latter are
doubled between apical plates 1' and 2', and 2' and 3', along the lateral margins
of the apical region, and in some specimens these two lists are continued (Plate
9, fig. 4) part of the way towards the girdle along the sutures between precingu-
lars 1" and 2", 4" and 5", and 5" and 6". Narrow intercalary zones have been
seen in some specimens, while in others only narrow ribs occur at the sutures.
The anterior intercalary is an irregular quadrilateral in the second quarter of the
left shoulder above the girdle on the dorsal side. Postcingular 7" ' is almost
quadrangular and is widely expanded in the girdle. Six girdle plates were defin-
itely located in this species.

The surface is only partially reticulated. The parts exempt from this differ-
entiation are the distal members of the precingular row of plates, the postcingu-
lars, and the ventral antapicals in part. There seems to be a tendency for the
reticulations to develop from the flagellar pore and sulcus to the left, around the
body in the direction of the girdle, and also to the right, but less markedly (see
Plate 9, fig. 2, 4, 7). The reticulations are not uniform in size or pattern, but
have a very characteristic facies due to the prevalent tendency to form rectangles,
especially along suture lines between the apical plates and at the precingular edge
of the girdle. There are about twenty-five polygons between the girdle and apex
along the midventral suture. The number of i-ows of jxilygons in any plate is
less than in the closely i-elated H. curvaium. The polygons each bear a central
pore. Pores are also sparsely scattered over the non-reticulate areas and in the
girdle.

The cell contents are unknown.

Dimensions: — Length, 249 (220-275) m; transdiameter, 139 (128-160) m;
length of right antapical, 58 m; of left antapical, 62 fx.

SYSTEMATIC ACCOUNT 77

Variation: — There is a wide range in dimensions in our specimens. The
maximum size (275 ju) was in a specimen from Station 4691 at a surface tempera-
ture of 73°, while one from 4724 at 79° measured only 220 m- There is also some
variation in the degree of curvature of the apical, the slenderness of the antapical
horns, and the extent of the reticulations. Murray and Whitting's (1899)
figure shows faint partial polygons in the girdle. One of our specimens had the
proximal 0.25 of the girdle reticulate. Secondary polygons were seen in one speci-
men with wide intercalaiy zones.

Comparisons: — This is the largest, and the terminal species in the H. dispar
group, and has the most specialized form as shown in curvature of the horns, elon-
gation of the sulcus, fins on the sutures and sulcus, and modifications in the pat-
tern of the reticulations. For comparisons with the nearly related H. curvatum
see that species.

The type locality is the Carribean Sea between Jamaica and Colon (Murray
and Whitting, 1899).

Occurrence: — Heterodinium hlackmayii is recorded (Plate 13) at eleven of the
127 stations. There are 1, 0, 1, 6, 3, and 0 stations respectively on the six lines
of the Expedition. Of these eleven stations, one (4596) is in the Mexican Cur-
rent, three (4691, 4697, 4699) are in the Easter Island Eddy, and seven (4701,
4705, 4706, 4707, 4732, 4734, 4739) are in the South Equatorial Drift. At two
stations (4596, 4706) the species was taken in surface hauls. All other records
are from hauls from 300-0 fathoms.

The temperature range of these eleven stations at the surface was 72°-84°
and the average was 75.8°, a relatively high average.

The frequency is 1% only at Station 4707. At all other stations it is less.

This species has been reported previously by Murray and Whitting (1899)
from eleven stations in the tropical Atlantic between 10°-25° N? and 44°-80° W.
from April to December in temperatures of 70°-82°. Karsten (1907) reports it
from five widely separated stations in the Indian Ocean between 7° N. and 30° S.
and 85°-96° E. in hauls within fifteen meters of the surface, except one haul from
200-0 meters.

This is a eupelagic, not widely eurythermal, species of wide distribution in
tropical seas. Our data in contrast with Karsten's (1907) suggest a relative in-
frequency in surface waters.

78 THE DINOFLAGELLATA

The rigdenae group
Plate 5, fig. 1 , 4 ; Plate 13 ; Plate 15, fig. 16-19; Plate 17, fig. 42-47 ; Plate 18, fig. 4S-r3l

Epitheca in ventral view not contracted into an apical horn, or with ex-
tremely short horn, low and wide (not less than 80°) ; antapicals short and stout.

This group contains four species, H. rigdenae Kofoid, H. crassipes Schiller,
H. scrippsi Kofoid, and H. Irirostre (Murray and Whitting). Only the first and
third occur in the collections of the Expedition.

Heterodinium rigdenae Kofoid
Plate 5, fig. 4; Plate 15, fig. 16; Plate 17, fig. 42-47

H. rigdenae Kofoid, 1906, p. 356-357, pi. 18, fig. 6-8; Karsten, 1907, p. 295.
H. loiigum Kofoid, 1907, p. 165, 183, pi. 7, fig. 44.
H. rigdunoe, Karsten, 1907, p. 473.

Diagnosis: — A medium-sized angular species of pentagonal outfine, oblique
axis; dorsoventral diameter 0.6 transdiameter, length 1.6 transdiameters;
epitheca erect, conical; antapical horns short, stout, subequal, flaring, pointed;
surface irregularly reticulate. Length, 120 (110-135) n. Rare in Eastern
Tropical Pacific, CaUfornia Current, Indian Ocean, and Mediterranean Sea.

Description: — This is a stout, quite angular species with the body in ventral
view roughly pentagonal, and much flattened for the whole of its length which is
1.28-1.60 transdiameters. The dorsoventral flattening reduces that diameter to
0.6 the transdiameter. The epitheca in ventral view is a flattened cone (70°-90°),
as a rule without apical horn, though in a few individuals there is a slight apical
contraction differentiating a short horn not over the diameter of the apex in
length. The sides are usually ciuite straight, though sometimes the right, or
even both, may be slightly concave. In lateral view the apical horn is differen-
tiated from the midbody by contraction at the apical-precingular suture. Bas-
ally in this view it is a low asymmetrical cone (90°), tilted dorsally with short,
slightly convex dorsal, and longer, concave ventral slope. From this arises the
stout conical (30°) apical horn with concave ventral, and convex dorsal side and
squarely, or obliquely truncated apex.

The midventral suture is angled at the apical-precingular suture and meets
the apex a little to the right of the middle. The ventral area is quadrangular
with a reniform ventral pore with the concavity facing to the right almost mid-
way between apex and girdle.

SYSTEMATIC ACCOUNT 79

The hypotheca is slightly shorter than the epitheca, basally subconical
(45°) with concave right and convex left margin and deep wide ventral excava-
tion. In lateral view it is subconical (35°) with concave ventral and convex
dorsal contour wdth an angle at the postcingular-antapical suture.

Distally it bears the two (^uite stout antapical horns. These are conical,
the right 33°-50°, the left 40°-G0°. The tips vary from acute to blunt, and some-
times have very small terminal spinules. They are deflected outwardly from the
vertical, the right 15°-22°, the left 15°-32°. The right is sometimes curved out-
wardly. They vary greatly in length, the right being generally a bit the shorter.
In very stout individuals the length is scarcely 0.20 transdiameter while in the
more slender ones it attains 0.37 transdiameter. The width between tips is
0.38-0.65 transdiameter. The postmargin is asymmetrically concave, often
tending towards a subangular (70°-90°) outline. Its depth is 0.18 to 0.30 trans-
diameter and there is no marginal hst.

The girdle is submedian, tilted posteroventrally 15° from the horizontal,
deflected posteriorly at the distal end a girdle width, and without any overlap.
The precingular ridge is a stout angular projection with a heavy rim, but the post-
cingular is equally developed only in the proximal quadrant. Elsewhere it is
reduced to a low ridge which almost vanishes in the distal quadrant. The furrow
is asymmetrically impressed, deeper anteriorly, and fades out distally.

The sulcus is straight and narrow, its length being about 0.33 transdiameter.
It lies towards the left side of the ventral depression and has no prominent lists.
Its distal end invades the postsulcal depression for nearly half its width. This
depression is guarded by high ridges developed on the midventral surfaces of the
two antapicals.

The plates are, as a rule, very clearly marked out by narrow suture ridges
which, as ecdysis approaches, expand into intercalary zones (Plate 5, fig. 4).
The lateral interapical sutures bear low fins. Anterior intercalary 1" is a trian-
gular quadrilateral which often has a partial exposure on the ventral surface as
well as the usual dorsal one. It is located a Uttle below the second quarter of the
left shoulder. Postcingular 7" ' is subtriangular, with an unusually wide base
with the hypotenuse sloping towards the flagellar pore. It often lacks all reticu-
lations.

The wall is reticulate, sometimes throughout, sometimes lacking these mar-
ings on the whole, or a part, of postcingular 7" '. The polygons are subregular
with a tendency for considerable local irregularities in size. The mesh is promi-
nent and the larger polygons are always porulate. In the girdle there are two

80 THE DINOFLAGELLATA

rows, the lower being the larger. Secondary non-porulate polygons appear along
both sides of the widening intercalary zones as ecdysis approaches (Plate 5, fig. 4).
There are twelve polygons along the midventral suture between apex and gii'dle
and twenty across the dorsal side at the girdle.

The plasma is very hyaline and completely colorless, or it may contain a few
irregular, or reniform, pale greenish-yellow chromatophores.

Dimensions: — Length, 118 (95-140) n; transdiameter, 80 (60-94) /u; dorso-
ventral diameter, 55 ix] length of right antapical, 22 (15-25) fi; of left antapical,
26 (19-35) fx. The largest individual (140 ju) is that figured on Plate 5, fig. 4,
which is in the stage preparatory to ecdysis. All others are 125 ^ or less.

Variation: — The material of the Expedition is quite variable in size, in
length, divergence and size of antapicals, and in shape of the postmargin. Tlie
figure (Plate 5, fig. 4) here published is unusual in that the thecal reticulations
which include the secondary polygons on the intercalary zones, and the propor-
tions, are distorted, mainly in length, by the expansion due to approaching ecdysis.

Comparisons: — Heterodinium rigdenae is much like H. crassipes, the
second member of the group, in habitus and thecal surface, but differs in stouter,
relatively wider body, much narrower and shorter ventral area, in the shorter
sulcus not extending to the postmargin, and lack of overhang in the girdle. It
differs from H. scrippsi in the absence of angles on the shoulders, less dorsoventral
flattening, less development of fins on sutures, less angled ventral suture, and
straighter sulcus. Of the species in the expansum group, it is most like H. hind-
marchii in surface markings and antapicals, but is shorter, stouter, and has less
elongation of epitheca and of antapicals.

Synonymy: — Helerodinium longum was described by Kofoid (19U7a) from
Stations 4732, 4734, and 4742. One of the specimens on which it was founded is
figured in Plate 5, fig. 4. This figure shows wide intercalary bands along the
suture lines. These bands were not shown in the figure of H. lonqiiin (1907a,
1)1. 7, fig. 44) accompanying the original description. Examination of the genus
as a whole has led us to the conclusion that ecdysis rather than binary fission is
prevalent in Heterodinium. We have concluded that H. longum is based on
specimens approaching ecdysis, and therefore somewhat more elongated, due to
expansion resulting from the growth of the transverse intercalary zones, and had
secondary reticulations spreading over these zones. We therefore reduce H.
longum to a synonym of H. rigdenae.

The type locality is in the California Current off San Diego, California
(Kofoid, 1906a).

SYSTEMATIC ACCOUNT 81

Occurrence: — Heterodinium rigdenae is recorded (Plate 13) at twenty-three
of the 127 stations, the maximum record for the genus. There are 3, 6, 1, 5, 7,
and 1 stations respectively on the six lines of the Expedition. Of these stations
two (4580, 4583) are in the Mexican Current, three (4613, 4637, 4038) are in the
Panamic Area, four (4647, 4650, 4659, 4664) are in the Peruvian Current, four
(4691, 4695, 4697, 4699) are in the Easter Island Eddy, one (4715) is in the Gala-
pagos Eddy, eight (4701, 4717, 4724, 4730, 4732, 4734, 4737, 4739) are in the
South Equatorial Drift, and one (4742) is in the South Equatorial Current. No
specimens were taken in surface hauls. It was taken at two stations (4724, 4732)
in hauls from 800-0 fathoms, and at Station 4732 and the twenty-two others in
hauls from 300-0 fathoms.

The temperature range at these twenty-three stations was 68°-83° and the
average was 75.8°, rather a high average. Of the twenty-three records, seventeen
are between 75° and 83°.

The frequency at three stations (4695, 4724, 4737) is 1%; at the other twenty
it is less. Twenty-six specimens were seen.

Heterodinium rigdenae was described by Kofoid (1906a) from the California
Current off San Diego where it was taken in June in hauls from 90 to 100-0
fathoms, but never in the numerous surface collections made in that region. It
is absent from the surface collections of Murray and Whitting (1899) from the
tropical Atlantic. Karsten (1907) reports a specimen from the Indian Ocean
near the Seychelles Islands in a haul from 200 m.

This is a eupelagic, widely eurythermal species from the subsurface of tropi-
cal and warm-temperate seas. Its occurrences in the Peruvian and California
Currents are suggestive of a wide disti'ibution in warm temperate currents, and
the large number of record stations and the frequency records of 1% indicate that
it is among the most abundant and widely distributed representatives of this
sparsely represented genus.

Heterodinium scrippsi Kofoid
Plate 5, fig. 1; Plate 15, fig. 18; Plate 18, fig. 48-51

Heterodinium scrippsi Kofoid, 1906a, p. 342, 344, 345, 347, 351, 359-360, pi. 17, fig. 1-5, Fig. A, B;

Karsten, 1906, p. 187, 194; 1907, p. 419, 450, 471; Lindemann, 1928, p. 95-96, fig. 82.
Peridinium areolatum Karsten, 1906, p. 150, pi. 23, fig. 18a, b; p. 150, footnote, Karsten states

" = Heterodinium scrippsi Kofoid".

Diagnosis: — A medium-sized species of robust, angular habit; length, 1.5
transdiameters; epitheca considerably larger than hypotheca with slightly emer-

82 THE DINOFLAGELLATA

gent horn; anterior intercalary near girdle facing on precingular 3"; sulcus not
over 0.5 distance from girdle to postmargin ; sutures often with ribbed lists, ven-
tral pore at anterior end of ventral area. Length, 130-155 n. Eastern Tropical
Pacific, California Current, and tropical Atlantic.

Description: — This is a medium-sized to large species with very robust but
angular facies. Its length is 1.4-1.5 transdiameters. The dorsoventral diameter
is 0.6 transdiameter. The ventral view is heptangular but the lateral reveals the
broadly bulging midbody on the dorsal margin. The epitheca is distinctly larger
than the hypotheca, its length being 1.4 that of the hypotheca and its lateral ex-
pansion relatively greater. The epitheca in ventral view is pentagonal, its length
0.75-0.80 transdiameter. Its lateral outhnes are marked by symmetrical or
subsymmetrical expansions at 0.3 of the distance from the apex to the girdle in
rounded shoulders so that the apical area has the lateral contour of a cone of ap-
proximately 90°. The right shoulder is usually a little more angular than the
left. Below this level it narrows to about 40° and flares abruptly at the girdle,
more on the left than on the right side. In lateral view the two faces are very
different. The ventral is flattened and excavated like a scoop. The dorsal is
concave, flaring below the apical-precingular suture into the dorsally globose mid-
body. The asymmetrical apical horn thus set off is recurved dorsally and is
roughly subconical (45°), flaring basally into the midbody. The apical horn is
slightly emergent in ventral view, but its length scarcely equals the diameter of
the squarely truncate apex.

The midventral suture is a narrow tract with a slight deflection to the left
at the oblique rectangular ventral area located immediately below the middle of
the epitheca. The ventral pore is subcircular, or broadly reniform with the con-
cavity directed anteriorly.

The hypotheca in ventral view is subconical (50°) with concave right and
convex left outline. In lateral view it is subhemispherical dorsally and deeply
depressed in the sulcal region ventrally. Its length is 0.65 transdiameter.

The antapical horns are short, stout, conical, sharp pointed, and unequal.
The right is the smaller, 0.2 transdiameter in length, a symmetrical cone (30°),
and deflected to the right 15° from the vertical. The left is stouter (45°-55°),
less deflected (7°), and longer (0.35 transdiameter in length). The postmargin
is very asymmetrically concave, deepest at the right, and generally bears a
coarsely reticulate and ribbed fin. The distance between the tips is 0.4-0.5, and
the depth of the indentation 0.18-0.20 transdiameter.

The plates are clearly marked, either by a nairow raised rib somewhat

SYSTEMATIC ACCOUNT 83

heavier than the adjacent mesh, or by this and an expanding intercalary zone
along one side of the rib, usually the median or the anterior side. In some
specimens the ribs bear a low fin into which adjacent bars of the reticulum are
extended as tapering riblets. These fins first appear on the lateral interapical
sutures, the postmargin, and later on other vertical sutures along stream lines
parallel to, or not opposed to the axis of progression. The anterior intercalary
is exposed wholly on the dorsal side. It is unique in the genus in being much
more widened at the mesial, usually quite narrow, end. The widening is not
quite enough to make the plate rectangular, but it does take up nearlj^ 0.5 of the
left side of precingular 3". Postcingular 1" ' is an elongated, rather irregular
plate, nearly twice as long as wide, and not much contracted in the girdle. It is
free from reticulations in all specimens thus far seen.

The surface is rather coarsely and heavily reticulated, with porulate poly-
gons of subuniform size, smallest at the girdle, generally pentagonal, with a
tendency to quadrilateral form near sutures. There are 10-12 between girdle
and apex along the midventral suture, fifteen along the middorsal region, and
twenty-three along the dorsal side of the precingular ridge. Secondary polygons
have been seen only in a few individuals along a few of the sutures.

The cytoplasm and the whole organism are very transparent. The ellip-
soidal nucleus hes near the flagellar pore. Adjacent to this are a few, small,
subspherical, pale greenish chromatophores.

Dimensions: — Expedition specimens: length, 140 (135-145) m; trans-
diameter, 97.5 (95.0-100.0) n; length of right antapical, 16 (15-17) m; of left
antapical, 27.5 (25-30) m- San Diego specimens: length, 140-155; transdiameter,
100-105 m; dorsoventral diameter, 60 yu; length of right antapical, 20 m; of left
antapical, 26 m- The magnification of the figures of the San Diego specimens
(see Kofoid, 1906a, p. 364, pi. 17, fig. 1) is incorrectly given due to a typographical
error. It is 425, not 725 as stated.

Variatio7i: — Specimens from the Expedition collections vary in the degree
of rounding off of the lateral angles of the epitheca, in the extent of inequality of
the antapicals, in the numbers of polygons in given plates, and in the extent of
development of the fins along the sutures. Variations due to approaching ecdy-
sis affect the width of intercalary bands, the number of secondary jiolygons along
these zones, and the proportions of the body.

Material from San Diego (near Station 4571) is somewhat larger and more
heavily reticulated than that of the Expedition.

Karsten's (1906, pi. 23, figs. 18a, b) figures are crudely drawn showing only

84 THE DINOFLAGELLATA

a few of the suture lines. It appears that his ventral view (his figure 18b) repre-
sents the dorsal side (of the epitheca only) drawn as though it were the ventral,
an accident happening easily on a tilted specimen. The shoulders, in his ventral
view, are more rounded than in any of our material.

Comparisons: — This species is near the end of a side line, which we have
called the rigdenae group, which leads off from the dispar series and is differen-
tiated from that series by the stouter body, low conical, or angled epitheca, and
shorter antapicals. The angled shoulders diffeientiate H. scrippsi from the
others in the dispar and rigdenae groups, and, in fact, from all species of the
genus except H. angulatum of the globose expansum series. The latter species
has more widely set, stouter, equal antapicals. H. scrippsi attains a high degree
of pronounced reticulation and development of ribbed lists.

Synonymy: — Meter odinium scrippsi is the type species of the genus by the
author's designation. Karsten (1906) had discovered it in the collections of the
"Valdivia" and had called it Peridinium areolaium. He utiHzed Kofoid's name
for the species in his lists of species at stations but unfortimately published his
own manuscript name in the explanation of his plate.

Tlie type locality is in the California Current off San Diego, California
(Kofoid, 1906a).

Occurrence: — Heterodinium scrippsi is recorded (Plate 13) at ten of the 127
stations. These are widely scattered over the area explored by the Expedition,
there being 1, 1, 1, 3, 4, and 0 stations on the six hues. Of these ten stations, one
(4580) is in the California Current, one (4637) is in the Panamic Area, five (4681,
4701, 4732, 4736, 4739) are in the South Equatorial Drift, and three (4691, 4695,
4697) are in the Easter Island Eddy. The species was never recorded in surface
hauls. At all ten stations it was taken in hauls from 300-0 fathoms and at Station
4732 was taken also in a haul from 800-0 fathoms.

The frequency was 1% only at Station 4580. At the other nine it was less
than this.

The temperature range at the ten stations at the surface was 68°-81° and
the average was 76.1°.

This species was taken by Kofoid (1906a) off San Diego, near Station 4571,
in hauls from 95 fathoms in June. It was one of the commoner species of the
genus taken off San Diego, but was never abundant, only single individuals, as
a rule, being observed in any haul.

Karsten (1906) records it at two stations only of the "Valdivia" cruise.
These are at 6° N., 15° W. and 3° N., 3° W. west of the Gulf of Guinea in Sep tern-

SYSTEMATIC ACCOUNT 85

ber, in hauls from 200 m. He regards the species as a member of the "Schatten-
flora." He also reports (1907, p. 471) it from the Indian Ocean.

This species is eupelagic in warm-temperate and tropical waters from deeper
levels of the Ught zone, and is moderately eury thermal, and, like others of the
genus, is never abundant. The fact that only a single record attained 1% is
indicative of its relative infrequency.

Subgenus Platydinium Kofoid
Plate 14; Plate 16, fig. 26-40

Plalydinium Kofoid, 1906a, p. 351; Lindemann, 1928, p. 96.

The body is much flattened dorsoventrally. The epitheca is scoop-like
with the apex broadly and evenly rounded in ventral view; antapical horns are
well developed, though one of the two is suppressed in each of two species.

The type species of the subgenus Platydinium was not designated by Kofoid
(1906a). As described by him this subgenus included only H. scrippsi and
H. whittingae. Since H. scrippsi is now the type species of both the genus and
subgenus Heterodinium and is in this paper included in that subgenus, H. whit-
tingae becomes, and is here designated as, the type species of the subgenus
Platydinium.

This subgenus contains two groups, the pavillardi group without sinistral
lobe with eight species (Plate 16, fig. 26-33) and the gesticulatum group with the
sinistral lobe and with six species (Plate 16, fig. 34-40).

Key to the species of the subgenus Platydinium Kofoid

1. Epitheca nearly bilaterally symmetrical, antapicals balanced in size and position 2.

1. Epitheca symmetrical or asymmetrical, antapicals unequal in size and deflection 3.

2. Antapicals stout, incurved whillingae Kofoid.

2. Antapicals more slender, spreading 4.

4. Epitheca with deep precingular constrictions 5.

4. Epitheca with shallow precingular constriction, convex above agassizi Kofoid.

5. Epitheca subangular anteriorly, antapicals not over 0.5 transdiameter long fides Kofoid.

5. Epitheca flattened semicircular anteriorly, antapicals about 1 transdiameter long. . . . scotti sp. nov.

3. No sinistral lobe or denticles on hypot heca 6.

3. With sinistral lobe, or with left horn suppressed 7.

6. Postmargin horizontal, apical pore very much deflected to right 8.

6. Postmargin not horizontal and straight 9.

8. Antapicals subvertical, length of body, 85 m pavillardi nom. sp. nov.

8. Antapicals incurved, length of body, 140 m lalicindum Kofoid.

9. Right antapical not over 1 .5 girrlle width in length, much smaller than the left 10.

9. Right antapical 3 girdle widths in length laeve Kofoid and Michener.

10. Left antapical 0.3 transdiameter in length, conical astjmmetricum sp. nov.

10. Left antapical 0.4 transdiameter in length, abruptly pointed inaeqvale Kofoid.

7. One antapical suppressed 11.

86 THE DINOFLAGELLATA

7. Both antapicals present 12.

11. Right antapical suppressed dejormalum (Kofoiti).

11. Left antapical suppressed sinistrum Kofoid.

12. Right antapical distally recessed on median face extremum (Kofoid).

12. No distal recess on right antapical 13.

13. Both antapicals deflected to the right varicator sp. nov.

13. Antapicals not deflected to the right . 14.

14. No denticles at postcingular-antaiiical suture on sinistral lobe geslicvlalum Kofoid.

14. One to three denticles on sinistral lobe mediocre (Kofoid).

The pavillardi group
Plates 10; 11; 14; 18, fig. 52-55; Plate 19, fig. 56-58

This group is characterized by the entire absence of the sinistral lobe and
the accompanying compensatory shrinkage of the right margin of the hypotheca
to a concave margin. There are no denticles at the postcingular-antapical suture.
Both antapicals are always present.

This series includes eight species, of which the first is Heterodmium pavillardi
nom. nov. Pavillard (191G), described Heierodinium kofoidi from the Gulf of
Lyons but this specific name had been used a short time previously by Schiller
(1916) for another species of Heterodinium from the Adriatic. C'onsequently the
name H. pavillardi is substituted by us. The other species of this group are H.
asymmetricuni sp. nov., H. inaequale Kofoid, H. laeve Kofoid and Michener, H.
agassizi Kofoid, H. whitlingae Kofoid, H. laticindum Kofoid, and//, fides Kofoid.
With the exception of H. pavillardi from the Gulf of Lyons and H. inaequale from
the California Current off San Diego, all species of this series occur in the collec-
tions of the Expedition.

Heterodinium agassizi Kofoid
Plate 10, fig. 4-8; Plate 16, fig. 27

Heierodinium ogassizi Kofoid, 1907a, pp. 164, 178, pi. 6, fig. 35.
Perklinium venter Hensen, 1911, p. 174, fig. C 7, Tab. XVI.
Heterodinium Agassizi Hensen, 1911, p. 174.

Diagnosis: — A large species with an elongated symmetrical body, narrowly
ovate in outline, except for the postindentation ; length, 2.1 transdiameters;
epitheca 1.2 transdiameters in length in ventral view, with semicircular apical
outhne, slightly constricted above girdle, scoop-shaped; girdle with both lists
narrow; postsulcal trough narrow; antapicals straight, subequal, 0.5 transdiam-
eter in length; ventral suture straight, ventral area elongated; surface completely
and heavily reticulated, twenty-eight polygons along precingular rim. Length,
160 M- Rare in Peruvian Current, Easter Island Eddy, South Equatorial Drift
of Pacific and Equatorial Currents and Sargasso Sea of Atlantic.

SYSTEMATIC ACCOUNT 87

Description: — This species is noteworthy for its elongated, relatively nar-
row, scoop-shaped body, and lack of asymmetry. Its length is 2.01 transdiani-
eters at the girdle. The epitheca and hypotheca are subequal in length at the
midlateral line. Ventrally, the former is 1.3 the extreme ventral length of the
latter; dorsally, the hypotheca is 1.75 the length of the epitheca. The epitheca
in ventral view has a semicircular outUne in its anterior 0.5, and halfway between
this and the girdle constricts at the apical-precingular suture, to 0.94 the diameter
at the precingular list. The concavity is deeper on the right than on the left.
The epitheca is widest at about 0.3 of its length from the apex where it is 1.1
transdiameters wide. In lateral view both faces are concave, the dorsal equally
throughout, the ventral more in its posterior 0.66 than in the anterior. It is
broadly hollowed out into a shallow scoop-like shape. The epitheca is thus quite
thin anteriorly, its outline embracing an angle of 20° apically, increasing to 70°
basally, with the flare at the girdle. The apical pore is level with the margin
and lies symmetrically in the major axis. The midventral suture is vertical and
nearly straight. The ventral area is in the center of the epitheca above the trans-
verse suture and has the very unusual form of a long narrow tract whose length is
six times its width. The ventral pore is at its anterior end, and is broadly reni-
form with a shallow indentation, directed to the right.

The hypotheca in ventral view is subconical (25°) in outline with nearly
straight sides, the right a bit convex. In lateral view it has a subconical outline
(50° basally, decreasing to 15° towards the antapex), with concave sides passing
into the slightly tapering horns which contract to the pointed tips more abruptly
in this than in the ventral view. It is deeply depressed in the narrow, median
sulcal tract. This is only 0.2 transdiameter wide at the girdle, widens to 0.3
at the postmargin, curves to the left in its anterior half, and becomes more nearly
vertical posteriorly.

The antapical horns are very nearly equal in length and proportions. They
are conical (32°), with straight sides, and vertical. The right in some specimens
has a bit of outward deflection. Their length is 0.44, the distance between tips
0.44, and the depth of the indentation 0.44 transdiameter, respectively. The
indentation embraces an angle of 45° and its bottom foi-ms the almost symmetri-
cally rounded," very short, concave postmargin about 0.1 transdiameter wide.
No fin was found on the postmargin.

The girdle is submedian, is tilted posteroventrally 25°, and is relatively very
narrow, being only 0.06 transdiameter wide. It is quite uniform throughout, is
displaced distally only its own width, and is without distal overlap. The pre-

88 THE DINOFLAGELLATA

and postcingular rims are equally developed as projecting angles. The furrow is
impressed about 0.5 its width, more deeply anteriorly.

The sulcus is long, 0.4 transdiameter in length, extending 0.9 the distance
from girdle to postmargin, very narrow, nearly straight, deflected 10° to the left
from the vertical, and has only a low ridge on either side. It almost crosses the
postsulcal region which is deep and narrow, being less than 0.25 transdiameter in
its widest part.

The plates are marked by low lidges scarcely differentiated above the heavy
reticular mesh, becoming prominent only when expanded by secondary poly-
gons. Intercalary plate 1" is triangular, exposed only in dorsal view, fills nearly
0.8 of the lower third of the left shoulder, and crowds precingular 2" into a narrow
rectangular plate scarcely as wide as the adjacent girdle. Postcingular 7" ' is a rect-
angular plate, over twice as long as wide, not contracted in the girdle. A spear-
shaped platelet in the bottom of the sulcus runs towards the flagellar pore from its
anterior end which is revealed when the plates are parted. It is not known
whether this belongs to 7" ' or to the sulcus whose finer elements are unknown.

The surface is everywhere reticulated (except the ventral area) including the
girdle and postcingular 7" ' which in so many species remains perfectly smooth.
The polygons are coarsely porulate, i-emarkably uniform in size and in weight of
the rather heavy reticular bars, though smaller near the girdle and on the antapi-
cals. There are nineteen polygons along the midventral suture between apex
and girdle, thirteen in the corresponding dorsal region, twenty-six at the precingu-
lar rim, and over thirty in the girdle on the dorsal side. There are two rows in
the girdle but the anterior one is reduced in size. Secondary polygons appear in
some suture lines, but no intercalary zones have been seen. Serrate lists were
seen on the lateral interpostcingular sutures on one individual.

The theca and cytoplasm in life are translucent. Bright cadmium yellow
chromatophores were observed in one specimen.

Dimensions: — Four individuals measured. Length, 161 (155-172) fi;
transdiameter, 80.5 (75-88) Midorsoventral diameter, 05 n; length of right antap-
ical horn, 39 (35-50) n; of left antapical horn, 39 (35-50) n; width of girdle, 6.8
(5-10) M.

Variation: — Specimens from the Expedition collections are quite uniform
in the epitheca but vary more in the antapicals. In one large specimen (172 n)
from Station 4737 the antapicals were very long (50 fi, 0.6 transdiameter) and
more slender than in other specimens. A specimen from Station 4657 had a
much wider girdle (10 ju) and more oblique antapicals.

SYSTEMATIC ACCOUNT 89

Hensen's (1911) figure of this species (as Peridinium venter) is sketchily
made and inverted. It differs from our specimens in a much narrower indenta-
tion and shorter postmargin, less smoothly rounded apical contour, and is drawn
with indications of a very unusual amount of distal displacement of the girdle.

Comparisons: — Hcterodinium agassizi stands somewhat alone in the sub-
genus Platydinium. It has the rounded epitheca of H. pavillardi, H. inaequale,
H. asymmetricum , and H. laticincium, but has equal instead of unequal antapicals
and a heavily reticulated instead of a smooth surface, characters which the group
just cited all lack. It has more in common with H. ivhiltingae in its close-set
antapicals and reticulate surface, but differs from it in more slender body, and
in the lateral constriction of the epitheca. In this constriction, as well as in the
equal antapicals, it approaches H. fides, but has less constriction, more rounded
apical region, and less flaring antapicals. It is a sort of transition form be-
tween the smaller and simpler species and, in two directions, namely toward H.
whittingae and H. fides, towards more diversified ones.

Synonymy: — Hensen (1911) pubhshes a very imperfect and inverted figure
which he names Peridinium venter with the added statement "scheint mit Hetero-
diniuni Agassizi identisch zu sein." The girdle is incompletely shown, but with
indications of great displacement. The antapicals are very long and narrow and
the indentation very much narrower. The apical region is also more squarish and
the constriction lower clown. The divergences from our material are so great and
significant that we are skeptical as to the identity of his species with H. agassizi,
but, in the absence of critical evidence as to the structure of his specimens,
leave the matter in suspense pending a reexamination of Atlantic collections.

The tj'pe locality is Station 4699 in the Easter Island Eddy.

Occurrence: — Heterodinium agassizi is recorded (Plate 14) at seven of the
127 stations. There are 0, 1, 2, 3, and 1 record stations on the six fines of the
Expedition. Of these seven stations, one (4657) is in the Peruvian Current, two
(4691, 4699) are in the Easter Island Eddy, and four (4681, 4701, 4709, 4737)
are in the South Equatorial Drift. All specimens were taken in hauls from 300-0
fathoms.

The temperature range at these seven stations at the surface was eS^-Sl.S"
and the average was 72.9°.

The frequency was 1% at Station 4657, and less than that at the other six
stations. Two specimens were recorded at Station 4699.

The species is confined in our collections to deeper hauls in the Peruvian Cur-
rent and water derived largely from it, and the average temperature (72.9°) is low.

90 THE DINOFLAGELLATA

Hensen (1911) reports as Peridinium venter a species of Heterodinium which
is doubtfully H. agassizi. He records it at fifty stations with a computed total of
788 specimens. These stations were widely distributed throughout the tropical
Atlantic in the North (6) and South Equatorial (16) Currents, the Gulf Stream
Drift (1), Guinea (7), Florida (3), Canary (4), and Brazilian (4) Currents, and
Sargasso Sea (9).

This species is eupelagic, confined to deeper levels, and, in the Pacific, mainly
confined to the cooler areas of the South Equatorial Drift and Easter Island Eddy.
This stenothermal limitation is not borne out by the distribution of Hensen's
species, doubtfully referred here.

Heterodinium fides Kofoid
Plate 11, fig. 2, 4, 6; Plate 16, fig. 28; Plate 19, fig. 56-58

Helerodinium fides Kofoid, 1907a, p. 165, 177, 179, 180, pi. 7, fig. 45.

Diagnosis: — A medium-sized species, almost symmetrical; length, 1.5
transdiameters; epitheca scoop-shaped, with deep bilateral constrictions; hypo-
theca contracted; antapicals subequal, spreading; girdle slightly oblique, furrow
present, postcingular rim partly developed; anterior intercalary very large; sur-
face reticulated. Length, 120-125 y.. Rare in the South Equatorial Drift of
the Eastern Tropical Pacific.

Description: — This is a very unique species in the genus with body and
antapicals subsymmetrical and deeply constricted epitheca. The epitheca and
hypotheca are subequal in length, but the epitheca has the greater volume.
The epitheca is scoop-shaped, being deeply hoUowed-out ventrally. In ventral
view its length is 0.75 transdiameter. It is deeply constricted at the two sides
at about the level of the apical-precingular suture, contracting to 0.67-0.73
transdiameter, at 0.66 the distance from the apex to the girdle. The bay on
the left side is a bit higher up than the one on the right and its flare to the girdle
a little steeper than on the right. Anteriorly the epitheca expands asymmetri-
cally at about 0.25 transdiameter below the apex to about 0.95 transdiameter.
The apex subtends an angle of 110°-120° with slightly convex sides, and flares
towards the girdle at about 65°. The apical pore is median but tilted dorsally.
The midventral suture is angled at the apical-precingular junction and deflected
to the left. The ventral area is elongated, located just a little below the middle
of the epitheca, and has a broadly reniform ventral pore near its anterior end. In
lateral view the dorsal outline is concave, the apical region being deflected dor-

SYSTEMATIC ACCOUNT 91

sally 15°. The ventral outliDe is convex anteriorly and deeply concave poste-
riorly in nudventral view.

The hypotheca is 0.82-0.86 transdiameter in length, in ventral view having
the outline of a cone of about 85° basally, with subequal concave sides, deeper on
the right. Distally the sides become parallel and flare slightly in the distal parts
of the antapical horns. In lateral view the outline is subconical (75°), with an
angle dorsally at the postcingular-antapical suture, and a deep midventral exca-
vation.

The antapical horns are subequal, the left a bit stouter than the right, sub-
conical (right 15°-20°, left 25°-30°), pointed, and spread laterally distally 25° and
20° from the vertical. The postindentation is 0.30-0.45 transdiameter in depth
and the distance between tips 0.45-0.60 transdiameter. The postmargin is
abruptly concave, deepest at the right, and bordered by an irregularly denticu-
late fin.

The girdle is tilted posteroventrally 10°, displaced at its distal end posteriorly
its own width, and has no overlap. It is quite wide, 0.12 transdiameter across,
with well-developed pre- and postcingular ridges, the latter fading out in the
distal quadrant. These ridges are angular projections without fins. The furrow
is indented 0.5 its width but fades out distally.

The length of the sulcus is 0.75 the distance from the precingular rim to the
postmargin, convex to the left, narrow, with heavy borders. It invades the con-
cave postsulcal trough for half its length.

The plates are clearly marked by heavy ribs at the sutures. The anterior
intercalary is subquadrangular and not visible in the ventral view. The length
of postcingular 7" ' is nearly twice its width and it is rounded posteriorly. The
surface is heavily reticulated throughout, except on postcingular 7' " which is
smooth with a single line of pores. The girdle has two subequal rows of poly-
gons. There are fourteen polygons along the midventral suture in the epitheca
and about twenty-five on the dorsal side anterior to the girdle. The polygons
are fairly uniform in size with only a few exceptionally large ones. No secondary
polygons at sutures have been seen.

The cell contents are unknown.

Dimensions: — Two specimens measured. Length, 120-125 //; transdiam-
eter, 70-83 m; length of right antapical, 27-33 m; of left, 25-28 m-

Variation: — The main variations noted in our limited material are in the
depth and inequality of the constrictions of the epitheca, flare of the antapicals,
and depth and shape of the postmargin.

92 THE DINOFLAGELLATA

Comparisons: — Helerodiniwn fides is unique in the genus in having the deep
lateral constrictions of the epitheca. In other particulars, notably in the hy-
potheca, flare, shape and symmetry of the antapicals, and in the character of the
reticulations, it is closest to H. agassizi.

The type locality is Station 4728 in the South E(iuatorial Drift.

Occurrence: — Heterodinium fides is recorded (Plate 14) at five of the 127
stations. There are 0, 0, 0, 1, 4, and 0 stations on the six lines of the Expedition.
All five (4707, 4724, 4728, 4732, 4736) are near the center of the South Equatorial
Drift. It was not taken in surface hauls. All records are from hauls from 300-0
fathoms.

The temperature range at these five stations was 72°-81° and the average was
77.6°.

This species is eupelagic, stenothermal at the higher temperatures, and con-
fined to deeper levels.

Heterodinium whittingae Kofoid
Plate 16, fig. 29
Heterodinium whitUngae Kofoid, 1906a, pp. 343, 344, 346, 349, 351, 361, 362, pi. 19, figs. 11-14.

Diagnosis: — A very large species, body dorsoventrally much flattened,
ellipsoidal in outline in ventral view, notched on the left posterior margin ; length
1.4 transdiameters ; epitheca and hypotheca subequal; girdle very oblique and
very narrow; antapicals short, stout, incurved; anterior intercalary triangular;
ventral area minute; surface completely and unevenly reticulated. Length,
180 IX. Eastern Pacific in California and Peruvian Currents, Galapagos Eddy,
and South Equatorial Drift.

Description: — The body in ventral view is broadly elliptical, its length being
1.4 transdiameters. The elliptical outline is interrupted by the slightly emergent
apical pore, projecting girdle, the sharp notch on the left posterior arc where the
postcingular plate 2' " overhangs antapical 2" ", and the postindentation. The
body is very much dorsoventrally flattened, its diameter in that axis being only
about 0.5 transdiameter, or less, according to the amount of tilting. The oblique
diameter in the plane of the girdle is nearly 0.66 transdiameter. This flattening,
with the accompanying hoUowing-out of the midventral region, gives a scoop-
shaped form to the body, especially to the epitheca. The length of the epitheca
in ventral view is 0.58 of the total length and 0.8 transdiameter. Its lateral out-
Unes are symmetrically convex, with a little flare near the girdle. In lateral view

SYSTEMATIC ACCOUNT 93

both faces are concave, the ventral more than the dorsal. The apical region is
very thin due to the flattening, and the apical pore is carried over a little on the
dorsal side where it is slightly emergent. The midventral Une shifts to the left
about 0.1 transdiameter at the ventral area which is midway between apical and
flagellar pores. The area is scarcely differentiated from the junction of the suture
lines. It contains a centrally located, very minute, elongated, reniform ventral
pore.

The hypotheca in ventral view is 0.42 of the total length and 0.53 trans-
diameter. Its sides are more convex than those of the epitheca and less nearly
equal, the right being shorter and more convex, and the left having a projecting
tooth or a notch at the postcingular-antapical suture. In lateral view it is sub-
conical (about 25°), flaring near the girdle. The ventral surface is depressed
midventrally and the dorsal lacks the abrupt inset below the postcingular-
antapical suture so prominent in such species as H. spiniferum.

The antapicals are subequal, very stout, subconical, the right in ventral
view 55°, the left 45°, bluntly pointed, and incurved, their outer contour convex,
the inner straight and vertical. They are close-set, their tips being only 0.14
transdiameter apart. The right is the shorter, 0.16 transdiameter in length, and
the left, 0.21. The depth of the postindentation is 0.21 and its width 0.10 trans-
diameter. The postmargin is rounded and inclined to the right.

The girdle is very narrow, 0.05 transdiameter in width, widening to 0.14 in
its distal quadrant. It is a bit sinuous, is guarded by very heavy but low pre- and
postcingular ridges, is displaced at its distal end its own proximal width, and has
no overlap. The furrow is scarcely impressed into the body wall.

The sulcus is short, extending scarcely 0.5 the distance from flagellar pore to
tip of antapicals, and invading the postsulcal trough only a short distance. It is
bordered by heavy ridges, but no lists, and contracts distally.

The plates are set off by clearly defined suture ribs, except the girdle plates
and plate 7' " which, in the spread of the distal end of the girdle, is included with-
out a rib between itself and the adjacent girdle plate. Anterior intercalary 1^
is a small triangular plate exposed on both dorsal and ventral faces, but mainly
on the former. Postcingular 7' " is incorporated in the expanded distal end of
the girdle. The surface is reticulated throughout, including the girdle and a part
of postcingular 7' ". The region of this plate adjacent to the flagellar pore is poru-
late but not reticulated. The polygons are quite uneven in size, the smaller ones
being found along the girdle and anterolateral and posterolateral sutures. All
are porulate. No secondary reticulations at the sutures have been seen. There

94 THE DINOFLAGELLATA

are nineteen polygons along the midventral suture and 25-30 along the dorsal
side of the precingular list. The girdle has 1-2 rows proximally and 2-3 in the
distal quadrant.

The cytoplasm is very hyaline, fills only a part of the theca, and is much
vacuolated. The very small sphaeroidal nucleus is centrally located and is
scarcely 0.09 transdiameter across. One small pale-yellow chromosphere about
the size of the nucleus lies near it.

Dimensions: — Length, 180 n; transdiameter, 135 ix; dorsoventral diameter,
70 m; obhquely along girdle, 82 n; length of right horn, 25 ju; of left, 30 ix; diameter
of nucleus, 12 /i.

Comparisons: — Heterodinium whittingae is near H. laticindum, resembling
it in epitheca, oblique girdle, and incurved antapicals, but differs from it in being
reticulated instead of smooth, having equal instead of unequal antapicals, and a
narrow, instead of wide, postindentation. It is also larger and longer. The pro-
jection on the left posterior margin is prophetic of the extensive development of
that particular region in H. gesticulahim. The right anterior region is likewise
slightly fuller than the left, as in the latter species.

The type locality is off the San Diego Coast, California.

Occurrence: — Heterodinium whittingae is recorded (Plate 14) at eleven of
the 127 stations. There are 1, 3, 3, 3, 1 and 0 stations on the six lines of the
Expedition. Of these eleven stations, one (4583) is in the Mexican Current, two
(4634, 4638) are in the Panamic Area, one (4648) is in the Peruvian Ciu-rent, one
(4691) is in the Easter Island Eddy, one (4715) is in the Galapagos Eddy, and
five (4683, 4689, 4701, 4709, 4717) are in the South Equatorial Drift. No speci-
mens were taken in surface hauls. It was taken at Stations 4689 and 4701 in
hauls from 800-0 fathoms and at 4701 and the nine remaining stations in hauls
from 300-0 fathoms.

The temperature range at the eleven stations at the surface was 70°-83° and
the average was 74.4°.

The frequency at Station 4634 in the Panamic Area in a haul from 300-0
fathoms was 2%, at Stations 4691 and 4701 in the Easter Island Eddy and 4715
in the Galapagos Eddy it was 1%, all three in hauls from 300-0 fathoms. At the
remaining seven stations and also at 4701 at 800-0 fathoms it was less than 1%.

Kofoid (1906a) described this species from the California Current in a haul
from 85 fathoms off San Diego in July.

This species is eupelagic, eury thermal, limited to the deeper levels, and is
rather widely distributed in the tropical and warm-temperate Pacific. Its fre-

SYSTEMATIC ACCOUNT 95

quency is relatively high and its hyalinity, small amount of cytoplasm, small
chromatophore, and flattened shape are all suggestive of a deep habitat.

Heterodinium laticinctum Kofoid
Plate 10, fig. 3; Plate 16, fig. 30; Plate 18, fig. 52-55

Heterodinium laticinctum Kofoid, 1907a, p. 105, 182, pi. 7, fig. 46.
Peridinium dentatum Hensen, 1911, p. 174, fig. C, 16, Tab. XVII.

Diagnosis: — A large robust species with very broad and very oblique girdle;
length, 1.5 transdiameters ; epitheca semicircular in outUne; antapical horns in-
curved, unequal, the left 0.25 transdiameter long ; postmargin horizontal, straight;
postcingular rim present; surface smooth, pores numerous. Length, 140 n.
Rare in South Equatorial Drift of Eastern Tropical Pacific and Tropical
Atlantic.

Description: — This is a very robust and very asymmetrical species. Its
robustness is due to the broadly rounded epitheca and its asymmetry to the very
oblique girdle and unequal incurved antapicals. Its ventral outline, barring the
gap between the antapicals, is like that of a hen's egg, interrupted midway by the
indented oblique girdle. Its length is 1.5 transdiameters. The epitheca is
smaller than the hj^potheca. Its length at the lateral margin is 0.40, in ventral
view is 1.45, and in dorsal 0.15 that of the hypotheca. In ventral view the an-
terior outline is almost a perfect semicircle extending the curve a Uttle as it nears
the girdle. The apical pore is a bit depressed in the margin, deflected a Uttle to
the right (see ventral view. Figure 30) and is very small. In lateral view the
appearance is very different. The apical region is dorsally reflexed so that the
lateral interapical sutures are carried over into a dorsal exposure. The outline
of the epitheca in this view fills an angle of 70°. The ventral slope is almost
flat, with a midventral and a transverse depression at the apical-precingular
suture. The dorsal contour is deeply and regularly concave, becoming steeper
towards the apex.

The hypotheca in ventral view continues the ovate curve of the epitheca,
but contracts asymmetrically more rapidly on the right than on the left side, so
that the former is more convex. The sides, if straight, would make an angle of
45°. In lateral view the outUne is very angular at the postcingular-antapical
suture, more so dorsally than ventrally. The ventral face is flattened, concave,
but interrupted by the projecting suture, and rather deeply depressed midven-
trally. Dorsally the outUne is rapidly contracted and concave below the girdle
and flattens out in the distal 0.66 of the distance between girdle and antapical

96 THE DINOFLAGELLATA

suture. At this suture it turns almost at a right angle ventrally in a concave
contour to the tip of the ventrally deflected antapicals. The postcingular zone
in the main makes an angle of 35°.

The antapical horns are rather slender, tapering regularly to a sharp point,
unequal, and incurved. The right is about 0.5 the length of the left, conical
(35°), and 0.14 transdiameter in length. The left is also conical (25°), and 0.28
transdiameter in length. The inner contours of the two horns are almost verti-
cal and the postmargin horizontal and straight, except in the abruptly rounded
angles. It bears an irregularly toothed, rather wide fin. The depth of the in-
dentation is 0.20, and the distance between tips 0.31 transdiameter.

The girdle is unusually well developed in this species, perhaps better than
in any other species in the whole genus. Both pre- and postcingular rims are de-
veloped, the furrow is indented, it is unusually wide (12 m, 0.13 transdiameter
in width), its plates are clearly outlined by liea\^ bars at the sutures, and it is
rather completely porulate. It is displaced distally its own width and has no
distal overlap. The furrow is indented about 0.3 its width and fades out in the
distal quadrant. The pre- and postcingular lists are subequal, each a projecting
angle with a heavy suture rib on its margin. The suture hnes separating the
girdle plates are also heavily ribbed.

The sulcus is narrow, short, extending 0.6 the distance from girdle to post-
margin, with heavy ribs in its margins. The postsulcal ti'ough is bounded by the
suture ribs which run down the ventral sides of the antapical horns. The sulcus
invades this area which is laterally extended to 2.3 times its vertical length.

The plates are everywhere very clearly set off by distinct suture ribs which
on the hypotheca laterally and distally have low, hyaline, serrate fins. The
seven girdle plates are clearly marked off by ribbed sutures. The anterior inter-
calary 1* is a small, almost rectangular plate in the second fifth of the margin of
the left shoulder. Postcingular 7"' is almost square and widest in the girdle.
The surface is completely devoid of any trace of reticulations in all specimens
seen. It is rather completely porulate over the whole surface. There are
twenty-three pores behind the girdle below the ]3ostcingular rim on the dorsal
side and two rows in the girdle.

The cell contents in life are very hyaline and include the centrally located
ellipsoidal nucleus and a very large, pale yellowish, spherical chromosphere an-
terior to which was a small pusule from which a sinuous outlet runs to the apical
pore.

Dimensions: — One specimen measured. Length, 145 ^; transdiameter,

SYSTEMATIC ACCOUNT 97

103 n] dorsoventral, 83 ix; obliquely along girdle, 92 y.; length of right antapical,

17 m; of left, 35 m.

Variation: — Our own scanty material of this species showed no marked
variations. Hensen's crudely drawn and inverted figure shows that the antapi-
cals are more nearly equal, but in other particulars the figure is remarkably simi-
lar to ours in structural features.

Comparisons: — Hetcrodinium laticinctum is next to the largest of the series
including also H. paviUardi, H. inaequale, and H. asymmetricum , all of which have
the semicircular outhne of the epitheca and unequal, straight, or incurved antapi-
cals. It differs from them all in the fuller development of the girdle rims, the
incurved antapicals, and the degree of development of lists. It differs from
H. whiUingae, the terminal and largest member, in the absence of reticulations,
wider postmargin, wider girdle, and quadrangular instead of triangular, anterior
intercalary plate.

Synonymy: — Hensen (1911) figured this species from the collections of the
"Valdivia" as Peridiniuin dentaium.

The ty]3e locality is Station 4724 in the South Equatorial Drift.

Occurrence: — Hetcrodinium laticinctum is recorded (Plate 14) at five of the
127 stations. There are 0, 0, 0, 1, 4, and 0 stations on the six lines of the Expedi-
tion. Of these five stations, one (4697) is in the Easter Island Eddy and four
(4724, 4732, 4737, 4739) are in the South Equatorial Drift. No specimens were
found in any surface haul. All records are from hauls from 300-0 fathoms and
the frequency in all cases is less than 1%.

The temperature range at the five stations at the surface was 75°-82°, and
the average was 78.8°, a rather high average.

It was reported by Hensen (1911) as Peridinium dentatum from the collec-
tions of the "Valdivia" at eleven stations, located in the North (1) and South
Equatorial (6) Currents, the Sargasso Sea (3), and North Sea (1), the latter
probably carried in with the Gulf Stream water.

This species is rare in tropical waters, avoids the surface, is eupelagic and
appears to be stenothermal in the higher temperatures.

Heterodinium asymmetricum sp. nov.
Plate 10, fig. 1-2; Plate 16, fig. 31

Diagnosis: — A small, rather clumsily formed, asymmetrical species with
stout body; 1.13-1.49 transdiameters long; epitheca broadly and asymmetrically
rounded; antapical horns very short, very unequal, the right scarcely developed.

98 THE DINOFLAGELLATA

the left 0.3 transdiameter long, separated 0.55 transdiameter ; girdle oblique
(45°) with undeveloped postcingular rim; surface smooth, or with only a few
scattered pores. Length, 85-90 /x. Rare in the Eastern Tropical Pacific in the
Easter Island Eddy and the South Equatorial Drift.

Description: — In this small stout species the body in face view is almost
square with a curved anterior side formed by the outhne of the epitheca. The
length, apart from the horns, is 0.98-1.11 transdiameters. The body is much
compressed dorsoventrally, that diameter being only 0.5 the transverse. The
epitheca is a low, asymmetrical dome, about 0.3 transdiameter in height in ven-
tral view, and about 0.75 in dorsal view, with unevenly rounded lateral outhnes,
the right shoulder being steeper than the left and less regularly cui-ved. In
lateral view the dorsal outUne is symmetrically concave, with a httle flare at the
girdle, and the ventral straight and flat with a httle median excavation. The
midventral suture is vertical from the girdle to the ventral area and then curves
25°-40° to the right to the apical pore. The ventral area is an obhque squarish
area about midway between apex and flagellar pore. In its center is the small
reniform ventral pore. The apical pore is not emergent.

The hypotheca is a little larger than the epitheca, subconical (15°), and al-
most squarish in ventral view. The right side grows convex distally, the left is
straight, or sUghtly concave. In lateral view it is also subconical (15°) basally,
but at the postcingular suture slopes abruptly ventrally, parallel to the obUque
girdle.

The antapical horns are unequal, conical, sharp pointed, wide-set at the
posterior corners, and quite variable in size. The left is 0.20-0.42 transdiameter
in length, the right even more variable (0.06-0.12), sometimes quite undeveloped
beyond a shght point. The right is a broad cone (90°), and the left narrowly
conical (25°), tapering distally. The postmargin is an asymmetrical shallow
indentation (0.14-0.20 transdiameter) and the distance between tips is 0.52-0.60
transdiameter. The margin often bears a dentate fin.

The girdle is very oblique, its plane sloping ventroposteriorly 45°, narrow,
not displaced distally, and without overlap at the distal end, with a narrow over-
hanging precingular rim, but no trace of the postcingular one. There is no
furrow.

The sulcus is a small, narrow, straight groove extending less than 0.5 the
distance from the girdle to the postmargin without hsts. The postsulcal depres-
sion is broad, shallow, and delimited by suture ridges narrowing out to the tips of
the antapicals.

SYSTEMATIC ACCOUNT 99

The plates are very faintly marked by delicate lines, or, at the most, very
narrow ridges. No intercalary zones have been seen. The dorsal precingulars,
owing to the foreshortening of the dorsal face of the epitheca, are very narrow.
The anterior intercalary 1» is almost rectangular, is exposed wholly on the dorsal
face, and borders the second fifth of the left shoulder. The dorsal slope is so
foreshortened as to bring the dorsal edges of apicals 1' and 3' over onto the dorsal
face.

In all specimens seen, the thecal markings were confined to relatively few,
small, scattered pores. Not a single reticular bar has been seen on any specimen.
The only fin is the serrated one extending along the postmargin.

The theca and cytoplasm are very hyaline in life. An ellipsoidal nucleus,
0.2 transdiameter in length, lies in the center of the epitheca viewed ventrally.
Immediately behind and below it is a spherical, very pale yellow chromatophore.

Dimensions: ■ — ^Four specimens measured. Length, 95.5 (85-104) /j.; trans-
diameter, 70.2 (65-75) m; dorsoventral diameter, 36 (35-37) /x; length of right
antapical, 7 (5-9) m; left, 22 (15-27) m- Transdiameter measured along the
obUque girdle 52 n.

Variation: — This is most obvious in the relative lengths of the right antapi-
cal horn, distance between antapicals, and shape of the postmargin.

Cmnparisons: — The species described by Pavillard (1916) as H. Kofoidi,
and here renamed H. pavillardi (page 86), is very closely allied to H. asymmetri-
cum. In the latter the antapical horns are more widely set and divergent, 0.3
transdiameter between axes in H. pavillardi and 0.5 in H. asyminetricum. The
apical pore is much wider in the former, the left antapical horn is less robust than
in the latter, and its antapical region bears heavy serrated fins. In H. asym-
metricum this fin is limited to the postmargin between the horns. It is also close
to H. inaequale Kofoid, but differs from it in smaller size, 95.5 (85-104) n as com-
pared with 116-120 IX, in not having an emergent apical pore, and in the absence
of any displacement of the distal end of the girdle. In //. inaequale this is dis-
placed a girdle width. The postmargin of the latter has a central bay which is
lacking in H. asymmetricum.

The type locality is Station 4699 in the Easter Island Eddy.

Occurrence: — Heterodiniu7n asynimetric^im is recorded (Plate 14) at only
four of the 127 stations of the Expedition, 1 on the third, and 3 on the fourth line
of the Expedition. Of these four stations, two (4691, 4699) are in the Easter
Island Eddy, and two (4701, 4715) are in the South Equatorial Drift. The fre-
quency was in all cases less than 1%, and all records are from hauls from 300-0

100 THE DINOFLAGELLATA

fathoms. The surface temperatures at the four stations ranged from 72° to 75°
and averaged 73.8°.

It is eupelagic and rare.

Heterodinium laeve Kofoid and Michener
Plate 11, fig. 1, 3, 5, 7; Plate 16, fig. 33

Heterodinium laeve Kofoid & Michener, 1911, p. 284-285.

Diagnosis: — A large, hyaline, asyinmetrical species with narrow, oblique
girdle; length, 1.7 transdiameters; epitheca less than a semicircle in outline;
apical pore deflected dextroventrally ; right antapical about 0.5 length of left,
both incurved and deflected to the right, tapering to a fine point; postmargin
asyiTimetrically concave; no postcingular rim; no reticulations. Length, 150-
170 n. Rare in the Panamic Area, South Equatorial Drift, and Easter Island
Eddy.

Description: — This is a large, decidedly asymmetrical species with an ob-
lique girdle, long hypotheca pushed to the right, and antapicals deflected to the
left. The epitheca is about 0.5 of the hypotheca. In dorsal view its height is
0.33 transdiameter, a low dome, asymmetrically more convex on the right than
on the left side. The apical pore is not emergent, is deflected 25° to the right of
the median line, and lies over the apical margin on the ventral surface. In ven-
tral view, the epitheca is scoop-shaped with a wide symmetrical depression ex-
tending to the lateral interapical sutures. The midventral suture is angled
(130°) at the ventral area which is located a little below the middle as a small
quadrangular area with a minute, broadly reniform, centrally located ventral
pore. In lateral view the epitheca has a subconical (55°) outline with rounded
apex and nearly straight sides.

The hypotheca is quadrangular in all views with nearly straight sides above
the postcingular-antapical suture. Its departures from this shape are due to its
dextral deflection. In dorsal view its right margin is convex and bulging and its
left is straight and sloping 20° to the right. In lateral view its dorsal face is
straight, flaring abruptly dorsally at its antapical suture. Its ventral contour is
gently concave with a rather deep median depression. Below the antapical
suture it is squarely inset for 0.3 transdiameter on the right, and 0.2 on the left,
the antapical horns arising in line with its ventral face.

The antapical horns are unequal and sharp pointed, the right being about
0.5 the length of the left. The right has a straight outer margin and a concave

SYSTEMATIC ACCOUNT 101

inner one, is subconical (30° basally, 15° distally), and deflected 25° to the left.
The left is more tapering, subconical (20° basally, 10° distally), its outer margin
straight basally, convex distally, and the inner concave throughout. It is de-
flected 30°-40° to the left, but distally the tip is incurved to, or beyond, the verti-
cal. They are wide-set, the distance between the middle of their bases being 0.6
transdiameter and between their tips 0.85 transdiameter. The postmargin is
very asymmetrically concave, deepest towards the right, and often straight and
horizontal for nearly 0.5 transdiameter near its middle.

The girdle is very obhque, inclined ventrally nearly 45° from the horizontal,
displaced distally only 0.5 girdle width, and its ends scarcely meet. It is quite
narrow, its width being only 0.1 transdiameter.

The precingular rim is feebly developed as a projecting angle. There is no
postcingular rim at all, except a vague line in the proximal quadrant. The
furrow is entirely lacking.

The sulcus is narrow, straight, runs for 0.75 the distance between the girdle
and the postmargin, slightly invades the postsulcal trough, and expands shghtly
just below the flagellar pore which lies at the junction of sulcus and girdle. There
are no lists along its margins.

The plates are defined clearly by suture hues and, in some cases, by border
Unes of pores. Distinct suture ribs have been seen on the interpostcingular
sutures in one specimen. The plates are sparsely porulate. Only one Une of
pores occurs in the girdle. No lists of any kind were seen on the theca.

The whole organism is remarkably hyaline and transparent. The cell con-
tents are unknown.

Dimensions: — Four specimens measured. Length, 143 (125-155) m; trans-
diameter, 90 (75-100) /x; dorsoventral diameter, 62 y., obliquely along girdle, 73 m!
length of right antapical, 28 (25-30) n; of left, 58 (55-62) m-

Variation: — Beyond the considerable variation in size our material shows
also some variation in the absolute and relative length and degree of deflection
and curvature of the antapical horns, and in the flatness of the postmargin.
There is also much variation in the distinctness of the sutures and pores.

Comparisons: — Heterodinium laeve differs from H. gesticulatum in its greater
inequality of the antapicals, less inequality of the two sides of the hypotheca,
and the weaker precingular rim of the girdle.

The type locality is Station 4739 in the South Equatorial Drift.

Occurrence: — Heterodinium laeve is recorded (Plate 14) at nine of the 127
stations. There are 0, 1, 2, 4, 2, and 0 stations on the six Unes of the Expedition.

102 THE DINOFLAGELLATA

Of these nine stations, one (4637) is in the Panamic Area, five (4689, 4691, 4695,
4697, 4699) are in the Easter Island Eddy, and three (4701, 4730, 4739) are in the
South Equatorial Drift. Two of the three are clustered in or near the Easter
Island Eddy. No specimens were recorded from surface hauls. At the nine
stations it was recorded from hauls from 300-0 fathoms and at Station 4701 also
from 800-0 fathoms.

The temperature range of these nine stations at the surface was 72°-79° and
the average was 75°.

The frequency was 1% at Station 4699, and less than that at all others.

This species is eupelagic and stenothermal in the warmer South Equatorial
region of the Eastern Tropical Pacific with a center of occurrence in the Easter
Island Eddy. Its absence from the surface and its extreme hyalinity are indica-
tive of its limitation to the deeper levels.

The gesticulatum group

Plate 12, fig. 1-5; Plate 14; Plate 16, fig. 34-40; Plate 19; fig. 59-65;
Plates 20, 21, 22, fig. 82-85

This series is characterized by the presence of the sinistral lobe on the hy-
potheca, a deep concavity on the right margin of the hypotheca, overhanging
epitheca, and denticles at the postcingular-antapical suture on the left margin.
The series contains six species, namely, H. viediocre (Kofoid), H. sinisirum sp.
nov., H. deformatum (Kofoid), H. gesticulatum Kofoid, H. extremum (Kofoid),
H. varicalor sp. nov., all described from collections of the Expedition; and
H. scotti sp. nov. from the tropical Atlantic.

Heterodinium mediocre (Kofoid)
Plate 16, fig. 36; Plate 19, fig. 59-65; Plate 21, fig. 74

Helerndinium qeslindalum forma mediocris Kofoid, 1907a, p. 165, 181, pi. 6, fig. 39.

Diagnosis: — A large subsymmetrical species with broadly rounded apex,
shght precingular constriction on both sides; length 1.69 transdiameters ; epitheca
overhanging equally on both sides ; hypotheca longer, its sinistral lobe not promi-
nent, usually bidentate; antapicals short, stout; postindentation asymmetrical,
nearly a right angle, quite shallow; anterior intercalaiy quadrangular, precingu-
lar 2" wide, postcingular 7' " pentagonal ; surf ace reticulated. Length, 122-145 m-
Rare in the South Eciuatorial Drift, Easter Island Eddy, and South Equatorial
Current of the Eastern Tropical Pacific.

SYSTEMATIC ACCOUNT 103

Description: — The body is stout, robust, subsymmetrical, with subequal
epitheca and hypotheca in ventral view. Its length is 1.69 (1.57-1.88) trans-
diameters. The epitheca in ventral view is 0.80-0.94 and in dorsal 0.44-0.55
transdiameter in length, equalUng, or sUghtly exceeding, that of the hypotheca.
In ventral view its outline is irregularly semicircular anteriorly, deflected to the
right, and, in consequence, fuller than on the left. Its area is, however, greater
than a semicircle, since the height of the epitheca exceeds the radius which only
reaches to about the median ventral pore. The epitheca is widest at about the
level of the ventral pore, constricting unequally on the two sides, somewhat more
on the right than on the left side, and flaring again a little near the girdle. The
midventral suture bends to the left at the apical-precingular suture, making an
angle of 150°-160°, at the median quadrangular ventral area which has a central
reniform ventral pore. The apical pore and lateral interapical suture are carried
onto the ventral face by the ventral inclination of the apical region.

The hypotheca is large, its length in ventral view being 0.76-1.00 that of the
epitheca. In ventral view it is rather asymmetrical due to the sinistral lobe which
projects not over a girdle width at the postcingular-antapical suture which is
deflected posteriorly about 45°. The outline of the lobe is broadly rounded
without a large protuberant extension. It bears one or two small acute denticu-
lations, one anterior to the suture, generally present, and one on the posterior
side of the suture, less regularly present. The right margin is rather evenly and
sUghtly concave.

The antapical horns in ventral view are conical in outUne, subequal, quite
stout and unequally divergent. The right horn is the smaller, concave on its
outer margin, becoming concave distally, nearly straight on the inner, diverges to
the right 30°, and is subconical (30°-45°). The left antapical is much stouter
and a little longer, concave basally on the outer side, becoming straight distally,
and straight throughout the inner face. It is conical (55°-90°) and sharp-
pointed, as is also the right antapical. The lengths of the horns are quite vari-
able, the right ranging from 0.14-0.26 and the left from 0.24-0.48 transdiameter.
The postindentation is wide and very shallow, asymmetrically deeper to the
right, subangular (75°-90°), with a broad, coarsely serrated, marginal fin.

The girdle is slightly oblique. Its distal end is displaced posteriorly about
0.5 girdle width. Its proximal end is narrowed as it approaches the flagellar
pore and its distal end is sUghtly widened. It is rather wide, 0.17 transdiameter
in width, and has no overlapping of the ends. The precingular Ust is formed by
the very unusual overhang on all sides of the epitheca over the contracted hy-

104 THE DINOFLAGELLATA

potheca. The postcingular ridge is almost wholly lacking throughout, at least
as an elevation above the hypotheca, and the furrow is impressed less than 0.3
its width.

The sulcus is very short, 0.50-0.65 the distance from the flagellar pore to the
postmargin in length, almost straight, very narrow, and invades the postsulcal
trough only a short distance.

The plates are clearly marked by suture ribs. The anterior intercalary plate
1» is broadly quadrangular and confined to the dorsal surface. Postcingular 7' "
is pentagonal and elongated below the level of the postcingular ridge. The sur-
face is reticulated throughout in the same general pattern of the reticulated parts
of H. gesticulalum (Plate 12, fig. 1-3), but no intercalary zones, secondary reticu-
lations, or bald plates were observed in H. mediocre.

A spherical centrally located nucleus was detected in one specimen. In life
one specimen recorded at Station 4689 had a cluster of about a dozen minute,
spherical, yellowish-green chromatophores clustered about the central nucleus.
Dimensions: — Six specimens measured. Length, 131 (118-145) Mi trans-
diameter, 77.5 (70.0-85.0) m; length of right horn, 28 (10-35) m; of left, 32 (17-37)
fi; diameter of nucleus, 20 ix.

Variation: — This species varies (Figures 59-65) in the depth of constriction
of the epitheca; ventral deflection of the apical pore; length, spread, and deflec-
tion of the antapicals; number and degree of development of the sinistral den-
ticles; and the length, thickness, and deflection of the antapicals.

Comparisons: — This is the least modified of the H. gesticulalum group, with
the smallest, least recurved sinistral lobe, least deflection of the antapicals, and
shortest antapicals. Its postindentation is widest, attaining 90°, and shallowest,
a feature which is most characteristic. The one or two denticles on the sinistral
lobe are also characteristic, not having been seen on H. gesticulatmn, H. extremum,
H. dejormalum, or H. varicalor. H. mediocre resembles H. fides in having a con-
striction of the epitheca, but very much less of it. The sinistral expansion of the
hypotheca is very slight in H. fides and it is very much more symmetrical.

Synonymy: — Described as Helerodinium gesticulalum forma mediocris by
Kofoid (1907a).

The type is from Station 4742 in the South Eciuatorial Current.
Occurrence: — Helerodinium mediocre is recorded (Plate 14) at seven of the
127 stations. There are 0, 1, 1, 3, 1, and 1 stations on the six lines of the Ex-
pedition. Of these seven stations, one (4637) is in the Panamic Area, two (4689,
4699) are in the Easter Island Eddy, one (4715) is in the Galapagos Eddy, three

SYSTEMATIC ACCOUNT 105

(4689, 4706, 4724) are in the South Equatorial Drift, and one (4742) is in the
South Equatorial Current. All were taken in hauls from 300-0 fathoms at all
seven stations and also at one station (4701) from 800-0 fathoms.

The temperature range of these seven stations at the surface was 72°-79°
and the average was 75.1°.

The frequency was in all cases less than 1%, except at Station 4715 where it
was 1%.

This species is eupelagic, eubathmic, and stenothermal at the higher tem-
peratiu'es and seemingly limited to the warmest tropical currents of the Eastern
Tropical Pacific.

Heterodinium sinistrum sp. nov.
Plate 16, fig. 34; Plate 21, fig. 78

Diagnosis: — A large, elongated species with elongated, dextrally deflected
and constricted epitheca; length 1.92 transdiameters ; hy]iotheca shorter than
epitheca on the right, with left margin vertical to the level of the posterior den-
ticle of the flattened sinistral lobe; no right antapical, the left, vertical, broadly
subconical; postmargin nearly a right angle; suture between 1' and 1" deflected
sinistroposteriorly. Length, 142 /*. Rare in the Panamic Area of Eastern
Tropical Pacific.

Description: — A unique and highly aberrant species with dextral deflection
of the elongated epitheca, deficient right antapical, and vertically elongated left
antapical, all of which features tend to give an unusual elongation and a peculiar
asymmetry to the body. The epitheca in ventral view is 0.5 the total length,
but more than twice that of the hj^potheca to the middle of the postmargin. Its
length is 1.1 transdiameters. The anterior outline is broadly rounded, fuller
anteriorly at the right than at the left and flattened at the left, due to the de-
flection of the epitheca anteriorly to the right. The right margin is sUghtly
flattened and concave about midway, and the left is evenly convex to the level
of the apical-precingular suture, where, as on the corresponding suture on the
right side, there is a slight depression. The concavity is smaller than on the right,
and only a girdle width above the precingular rim. This inequality results from
the obliquity of the ventral transverse suture between the apical and precingular
plates. This suture is inclined sinistroposteriorly about 17°. The interapical
lateral sutures above this transverse suture appear to be finned and sparsely
ribbed. The midventral suture is deeply angled, 150°, with both arms oblique

106 THE DINOFLAGELLATA

to the vertical. The ventral area lies at the left of the median line, is quad-
rangular, squarish, located midway between girdle and apex, and contains an
anteriorly located, minute, reniform ventral pore with the concavity to the right.
The apical pore is deflected 5° to the right from the vertical. The epitheca over-
hangs the hypotheca a little more than 1.5 girdle widths on the right, but is with-
out overhang on the left.

The hypotheca in ventral view is equal to the epitheca on the left half, but
greatly reduced on the right. Its right margin is concave and the left is straight
and vertical to the level of the postcingular-antapical suture, below which there
is a posterior, backwardly deflected, rather long denticle. The right antapical is
reduced to a stout, scarcely projecting (0.5 girdle width), bluntly rounded lobe,
0.25 transdiameter wide at its base, and deflected laterally 40° from the vertical.
The left antapical is quite normal, except for its vertical position and its displace-
ment towards the median line. Its axis is almost in line with the ventral pore
and it is deeply and abruptly concave below the denticle. On its outer face it is
a stout, sharp-pointed cone (40° distally and 25° proximally), with a very shghtly
concave inner border. The postmargin is inverted L-shaped, almost right angled,
with the angle rounded, and is incUned to the right. Its left subvertical margin is
bordered by a wide irregularly toothed fin.

The girdle is incUned about 20° ventroposteriorly, is not displaced distally,
and has no distal overlap. Both the pre- and postcingular ridges are developed
subequally in the proximal quadrant, but the epitheca, without any marked pre-
cingular flare, overlaps widely on the right margin. The girdle abruptly widens
distally, as it reaches postcingular plate 7" ', to twice its width elsewhere. The
furrow is only shghtly impressed.

The sulcus, from the precingular ridge to its end, is 0.66 the distance to the
postmargin. It is deflected to the right 10° and, below the large flagellar pore, is
uniformly narrow and sinuous.

The plates are clearly marked by sutures. Postcingular 7" ' is very wide,
nearly two girdle widths, and pentangular. The dorsal view is not known, but
from the location of the apical-precingular suture on the right margin, it is evi-
dent that precingular 2" must be a very narrow plate.

The surface marking and cell contents are unknown.

Dimensions: — Length, 142 ^l•, transdiameter, 77 n; length of left antapical,

45 m.

Comparisons: ■ — Heterodinium sinistrum. is quite unlike all other species of
the genus in the suppression of the right antapical horn, and, in compensation, in

SYSTEMATIC ACCOUNT 107

the shifting of the right antapical towards the median hnc, the increase in vohinie
of that part of the epitlieca, and the deflection of the epitheca to the right with
resulting asymmetry. It is clearly near the gesticulatum group and perhaps near
H. fides. It is the counterpart of H. deformatum, in which the left antapical is
suppressed, but differs from it in proportions, notably greater elongation, and
marked asymmetry of the epitheca; in absence of displacement of the distal end
of the girdle; and in the shape of postcingular plate 7" '. With the median shift
of the left antapical, the sinistral lobe is flattened out so that the left margin is
vertical and the denticle is directed posteriorly. The oblifiuely posterior deflec-
tion of the ventral apical-precingular suture is not equalled in any other species.

The type locality is Station 4638 in the Panamic Ai'ea.

Occurrence: — Heterodinium sinistrum is recorded (Plate 14) at only one of
the 127 stations on the second line of the Expedition at Station 4638 in a haul
from 300-0 fathoms in the Panamic Aiea off the Galapagos Islands.

The temperature at this station at the surface was 75°.

The frequency was less than 1%.

This species is eupelagic, eubathmic, and rare.

Heterodiniitm deformatum (Kofoid)
Plate 16, fig. 35; Plate 21, fig. 73, 75, 76

Heterodinium geslicxdatum forttia deforrnata Kofoid, 1907a, p. 165, 181, pi. 6, fig. 40.

Diagnosis: — A medium-sized, stout, asymmetrical species with an expanded
epitheca, constricted at the left, with overhang of a girdle's width at the left;
length 1.67 transdiameters; hypotheca, excluding horn, less than the epitheca,
with very broadly rounded, scarcely developed sinistral lobe without denticle;
right antapical, long, tapering; left lacking; postmargin subhorizontal ; postinden-
tation right angled; surface as in gesticulatum. Length, 127 (123-130) ix. Rare
in the South Equatorial Drift of the Eastern Tropical Pacific.

Description: — This is a highly asymmetrical, medium-sized, stout species
wholly lacking the left antapical, and with only sUght development of the sinistral
lobe. In ventral view the length of the epitheca is 1.61 times that of the hy-
potheca (excluding the right antapical) and its wadth 1.24 times that of the
hypotheca. It has considerably the greater volume. Its length in ventral view
is 0.9 transdiameter. In dorsal view the epitheca and hypotheca are subequal.
Anteriorly the epitheca is subsemicircular in outline, fuller at the right than at the
left, and has a sUght constriction above the precingular ledge on the left, but none

108 THE DINOFLAGELLATA

on the right. About midway of the epitheca it expaiuls up to 0.59 girdle width
more than the precingular transdiameter. The apical pore is deflected about
10° to the right and is shoved over onto the ventral face. The epitheca over-
hangs the hypotheca 0.5 a girdle witlth at the right and about 1.0 at the left.
The midventral suture is angled 160° to the left and the ventral area hes on it
midway between the apex and the girdle. It is unequally quadrilateral, with an
anteriorly located, very small, reniform ventral pore, witli the concavity facing
to the right.

The hypotheca, exclusive of the right antapical, is about 0.5 transdiameter
in length, and has a concave right and left margin. Its sinistral lobe is scarcely
developed and is merged with the rounded and undeveloped left antapical region.
There is no denticle at the postcingular-antapical suture or, at the most, only a
faint indication of one. The right antapical horn is vertical, or deflected 25° to
the right, conical (25°), and sharp-pointed. There is no left antapical horn.
The postmargin is right angled, L-shaped with rounded corner, and with or
without a narrow, sparsely toothed fin. The depth of the postindentation is
about a girdle width.

The girdle is submedian, displaced distally about 0.5 a girdle width, and is
without distal overlap. It fades out distally. The precingular ridge is fairly
well developed as a slightly everted edge of the overhanging epitheca. The post-
cingular rim is deficient, being a slight elevation in the proximal quadrant only.
The furrow is indented only in the proximal part, the curve below the precingular
ridge being more pronounced in that region. The width of the girdle is 0.12-0.14
transdiameter and it flares in the distal quadrant.

The sulcus is very short, less than 0.5 the distance from the postcingular rim
to the postmargin in length, oblique, deflected 30° to the right, and has an over-
hanging tooth at the middle of the right margin.

The plates are clearly defined by distinct sutures. The anterior intercalary
1» has a horizontal width of 1.5-2.5 its vertical height and fills about the second
fifth of the left margin of the epitheca. It lies wholly on the dorsal face. Pre-
cingular 2" is about equal to it in shape and lateral extent. Postcingular 7' " is
obliquely quadrilateral and twice as long as wide. The postcingular-antapical
suture on the dorsal face is inclined sinistroposteriorly 20°-25°.

The surface marking and cell contents are unknown.

Dimensions: — Two specimens measured: length, 127 (123-130) /u; trans-
diameter, 82 m; greatest diameter, 86 (85-87) y.; length of right antapical horn,
41.5 (38-45) M.

SYSTEMATIC ACCOUNT 109

Variation : — Our two specimens differ in the obliquity of the right antapical
horn, the angle of the postmargin, and the width of the girdle.

Comparisons: — Heterodinium deformatum is unique in the genus in the sup-
pression of the left antapical. The shape of the epitheca and the slightly de-
veloped sinistral lobe, broadly rounded and fused with the antapical region, is
indicative of its affiliation with the gesticulaium section of the subgenus Platy-
dinium. It does not have the habitus of a mere abnormality, especially in view
of the diversification of this section as a whole. Furthermore, its characters,
aside from the left antapical, are not those of any species of the genus. It is
nearest to H. varicator, but has a different right antapical, anterior intercalary,
and sinistral lobe.

Synonymy: — The species was described as H . gesticulaium forma deformata
by Kofoid (1907a).

The type locality is Station 4724 in the South Equatorial Drift.

Occurrence: — Heterodinium deformatum is recorded (Plate 14) at only two
(4724, 4736) of the 127 stations, both on the fifth line of the Expedition from
hauls from 300-0 fathoms in the South Equatorial Drift.

The frequency was less than 1%.

The temperature range at the two stations at the surface was 79°-81° and
the average was 80°, a high level.

The species is eupelagic, narrowly stenothermal, and eubathmic in the center
of the East Tropical Pacific.

Heterodinium gesticulatxjm Kofoid
Plate 12, fig. 1-5; Plate 16, fig. 37; Plate 22, fig. 86

Heterodinium gesticulaium Kofoid, 1907a, p. 165, 180-181, partim.

H. gesticulatum forma typica Kofoid, 1907a, p. 105, 181, pi. 6, fig. 37; Hbnsen, 1911, p. 174.
Peridiidum tristylum Hensen, 1911, ]>. 174, fig. C, 10, Tab. XVII, non P. tristylum- Stein, 1883, p. [48],
pi. 9, fig. 15-17.

Diagnosis: — A large asymmetrical species with semicircular apical outline,
constricted at left above girdle, overhanging the girdle a girdle width at the
right; length 2.25 transdiameters ; hypotheca short with large lateral lobe on left
margin above postcingular-antapical suture; right antapical uniformly conical
(25°), without a distal bay on inner face; postindentation subangular, subtending
45°; anterior intercalary rather narrow, precingular 2" and postcingular 7' "
narrow; surface heavily reticulated except on left anterior region. Length, 130-
145 fi. Widely distributed in Eastern Tropical Pacific from the Mexican Cur-
rent to the Easter Island Eddy.

no THE DINOFLAGELLATA

Description: — The asymmetiy of this large species is accentuated by three
major structural features, (1) the overhang of the epitheca at the right precingu-
lar region, (2) the massive sinistral lobe below the girdle, and (3) the dextral
deflection of both antapicals. This results in a bizarre form of body which in
ventral view presents a normal dome-shaped epitheca but a much distorted
hypotheca. The length is 1.86-2.00 transdiameters and the dorsoventral diam-
eter about 0.75 the transverse measured on the precingular ridge.

The epitheca in ventral view is asymmetrically dome-shaped with a length of
0.95-1.11 transdiameters at the precingular ridge. Its outUne anteriorly is al-
most semicircular, a little fuller at the left. The right margin becomes almost
straight as it approaches the girdle, but on the left there is a slight constriction
above the girdle. In one specimen the expansion above the constriction slightly
exceeded the diameter at the girdle. In lateral view the epitheca is subconical
(60°) with the ventral side steeper and flatter than the more rotund dorsal side.
The midventral suture is almost straight, is inclined to the right anteriorly, and
has a median quadrangular ventral area with a minute bilobed ventral pore
centrally located.

The hypotheca is strangely distorted, so much so as to make description in
the usual terms diflficult. The massive left lobe has seemingly appropriated some
of the substance of the hypotheca and in consequence it appears that the right
side has collapsed inward, the main part has been foreshortened, and the antapi-
cals have been pulled basally towards the lobe with a resulting obliquity. In
ventral view the hypotheca is 0.85-0.90 transdiamejter in length and only 0.81-
0.84 transdiameter in width at the girdle, due to the overhang of the epitheca.
On the dorsal side it is a little less than one transdiameter in length. In ventral
view the right margin is cjuite concave but the left is expanded in a massive lobe
above the postcingular-antapical suture which is convex outwardly and turns
abruptly horizontally at a right angle at the suture. The angled tip of the lobe
is scarcely recurved posterioily. In lateral view the dorsal surface is basally
broadly convex, curving ventrally below the postcingular-antapical suture to the
antapicals which arise well towards the ventral face. Ventrally the hypotheca is
deeply excavated in the midventral region.

The antapicals are conical, pointed, unequal, spreading, and much deflected
to the right. The right is the longer, but more slender conical (20°), 0.57 trans-
diameter in length, and deflected 25° to the right. The left is much stouter,
conical (35°), blunter, 0.33 transdiameter in length, and is also deflected to the
right 10°. The postindentation is asymmetrical, deeper at the left, subangular

SYSTEMATIC ACCOUNT 111

(25°), with narrowly concave serrated postmargin scarcely more than a girdle
width wide. The distance between tips is about 0.5 transdiameter.

The girdle is submedian and in its proximal and distal quadrants curves
posteriorly. Dorsally it is almost horizontal. It is without distal overlap and
its distal end is displaced posteriorly less than 0.5 a girdle width. The precingu-
lar ridge is well developed throughout as a thick, angled, but very low shelf.
The postcingular ridge is almost wholly lacking. The furrow is only feebly im-
pressed and fades out posteriorly.

The sulcus is very short, almost comma-shaped, and does not extend below
the postcingular-antapical suture. It is without lists but is bordered by a heavy
rib.

The plates are marked by heavy suture ribs, and in the specimen figured on
Plate 12, fig. 1-5, the sutures between many of the plates have widened out in
intercalary bands. The lateral interapical sutures are carried over on the ventral
face. The anterior intercalary 1" is a very wide plate, broadly quadrangular, at
the expense of precingular 2". Postcingulars 1' " and 7' " are both small as a
result of the foreshortening of the basal part of the h^'potheca. Plate 7' " is
rectangular and scarcely longer than the girdle width.

The surface is coarsely and heavily reticulated, except on plates 1', 2', 5",
and the dorsal side of the two antapicals. Invading (or retreating ?) reticulations
are present on 1' and 2' adjacent to or bordering fully reticulated plates (Plate 12,
figs. 1, 4). These are only faintly outUned on plate 1'. There are fifteen poly-
gons along the nudventral suture, eighteen in the reticulated part on the dorsal
side, and twenty-eight on the ventral side anterior to the girdle. The polygons,
and also the area without reticulations, are porulate. Tlie girdle has an inter-
rupted series of 2-3 plates. Secondary reticulations appear in the intercalary
zones. A specimen without intercalary zones was reticulated throughout. The
curious irregularity in the distribution of reticulations seems not to be correlated
with fission or any possible fission-line. It occurs in connection with the appear-
ance of intercalary zones and might be a phase of resorption or of othei' legulatory
processes in conjunction with approaching ecdysis.

The cell contents in a preserved specimen include a very large (25 ft), spheri-
cal, centrally located nucleus, a chromosphere adjacent to it, and a cluster of
refractive (amyloid?) bodies gathered about the nucleus.

Dimensions: — Two specimens measured. Length, 142-170 n; transdiam-
eter at precingular ridge, 70-100 m; dorsoventral, 85 ^ (one specimen); length of
right antapical, 42 m) of left, 39-42 jx; diameter of nucleus, 25 ix.

112 THE DINOFLAGELLATA

Variation: — In the limited material of this species as here delimited, there
is some variation in size, in the relative lengths of the antapicals, in the depth of
the precingular constriction of the epitheca, in the extent of reticulation, and in
the presence of intercalary bands and secondary reticulations. The last-named
features are probably concerned with approaching ecdysis.

Comparisons: — Hcterodinium gesticuJaium belongs in the series with H.
mediocre, H. externum, H. dejormalum, and H. varicator. Its sinistral lobe is more
massive than in any of these species, and less recurved and less pointed than in
H. exiremum. Its antapicals are less deflected and longer than in H. varicator,
and the postindentation is narrower, more angular, and deeper than in H. varica-
tor and (except for depth) H. extremum. It lacks the abrupt diminution on the
inner face of the right antapical of H. extremum and the left antapical is not de-
formed or deficient as in H. deformatum.

Synonymy: — This species was described by Kofoid (1907a) with four di-
visions, each designated as a forma. As here delimited H. gesliculatum is re-
stricted to forma lypica Kofoid (1907a). The other divisions forma deformata,
forma mediocris, and forma extrema are raised to specific rank, as each has a con-
sistent group of differential characters mainly centering in the antapicals, post-
indentation, and sinistral lobe. A fourth species, H. varicator, is also segregated
out of the complex on the same grounds.

The type locality is Station 4594 in the Mexican Current.

Occurrence: — Heterodinium gesticulatum is recorded (Plate 14) at sixteen of
the 127 stations. There are 1, 1, 6, 5, 3 and 0 record stations on the six lines of
the Expedition. Of these sixteen stations, one (4594) is in the Mexican Current,
one (4634) is in the Panamic Area, ten (4G79, 4681, 4683, 4687, 4689, 4701, 4705,
4724, 4732, 4737) are in the South Equatorial Drift, and four (4691, 4695, 4697,
4699) are in the Easter Island Eddy. No specimens were taken in surface hauls.
It was taken in hauls from 300-0 fathoms at the sixteen stations and in addition
at Stations 4681 and 4689 also in hauls from 800-0 fathoms.

The temperature range at these sixteen stations at the surface was 68°-84°
and the average was 74.8°.

The frequency was 1% at Stations 4689 in hauls from both 300-0 and 800-0
fathoms, and at 4697. At all other stations it was less than 1%.

It was reported by Hensen (1911) as Peridinium tristylum in the collections
of the Plankton Expedition at nineteen stations with a computed total of 270
individuals. These stations were distinctly limited to tropical regions, two being
located in the North and seven in the South Equatorial Currents, respectively;

SYSTEMATIC ACCOUNT 113

two in the Florida Current; one in the Gulf Stream Drift; three in the Brazilian
Current; three in the Canary Current; and one in the Guinea Current.

This species is widely distributed in the Eastern Tropical Pacific and the
tropical Atlantic. It is one of the most prevalent, its record of occurrences (16)
being exceeded only by those for H. milneri (19), H. rigdenae (23), and H. cur-
vatum (17). It is eupelagic, eurythermal, and eubathmic. Its large size may
contribute to the frequency of its records.

Heterodinium extremum (Kofoid)
Plate 16, fig. 38; Plate 21, fig. 79-81; Plate 22, fig. 82, 83, 84

Heterodinium gesliculatum forma exlrema Kofoid, 1907a, p. 165, 181, pi. 6, fig. 38.

Diagnosis: — A large quite asymmetrical species with low, broadly rounded
epitheca, deeply constricted above the girdle on both sides; epitheca overhanging
more on the right than on the left; length, 1.83 transdiameters ; hypotheca short,
its sinistral lobe long, recurved, pointed, no denticles at the postcingular-antapi-
cal suture ; antapicals long, subequal, the right with an abrupt constriction on the
inner face, distance between tips less than 0.66 transdiameter ; postindentation
subangular (45°), asymmetrical, more than 0.5 transdiameter in depth; anterior
intercalary very wide, surface often incompletely reticulated. Length, 120-140 ai.
Rare in the South Eciuatorial Drift and Easter Island Eddy of the Eastern
Tropical Pacific.

Description: — This is a large, very asymmetrical, quite elongated species.
Its length is 1.80 (1.71-2.00) transdiameters. In ventral view the epitheca and
hypotheca are subequal in length, but the epitheca has the larger mass. The
asymmetry afTects the epitheca in the deflection of the apical pore to the right
15°, in wider overhang of the epitheca on the right side, and in the higher level
of precingular constriction on the right than on the left side. The epitheca in
ventral view is almost -semicircular in its anterior part, tilted to the right, and
constricted anterior to the girdle to a little less than the transdiameter. The
constriction is about two girdle widths above the precingular ridge on the right
and immediately above it on the left. The epitheca in ventral view has a length
of about 0.8 transdiameter, and its greatest width (1.09-1.18 transdiameters) is
found obliquely about midway of its length. In dorsal view its length is about
0.66 the ventral length. The most outstanding feature is the wide and abrupt
overhang of the epitheca beyond the hypotheca. This is at least a girdle width
at the left margin and may be as much as two girdle widths at the right. The

114 THE DINOFLAGELLATA

midventral suture is somewhat angled (140°-160°) and is slightly below the
middle of the epitheca. The ventral area is a very small quadrangular region
with a minute, stout, reniform ventral pore.

The hypotheca is narrower and, in ventral view, a little shorter than the
epitheca. In dorsal view its length is 0.56 that of the epitheca and approximates
the transdiameter at the precingular ridge. The hypotheca is widest at the level
of the sinistral lobe. The width of the postcingular margin is only 0.66-0.90
that of the precingular ridge, due to the wide and variable overhang of the epi-
theca. The width at the sinistral lobe is over 0.9 transdiameter. The hypotheca
is very asymmetrical, due to the lateral extension of the sinistral lobe and the
compensatory concavity of the dextral border. The sinistral lobe lies above the
postcingular-antapical suture. It is an angular projection, recurved posteriorly,
with very pointed tip from one to two girdle widths long.

The antapical horns are long, somewhat divergent, sharp pointed, and are
both deflected strongly to the right. The right horn is 0.67 (0.61-0.74) trans-
diameter in length, 1.1 longer than the left. It is uniform in width in the proxi-
mal 0.66 of its length, 1.0-1.5 girdle widths in diameter, and contracts abruptly
on the inner face only, with a concave curve, to a slender tapering point about a
girdle width in length. It is deflected 25°-30° from the vertical to the right.
The left antapical is symmetrical, conical (25°-35°), pointed, and is deflected to
the right into a vertical position, or even slightly beyond it. Its length is
0.59 (0.55-0.64) transdiameter and the distance between tips is about 0.8 trans-
diameter. The post indentation is asymmetrical, deepest at the right, subangu-
lar (50°-60°), and has an asymmetrically concave, rather short postmargin.

The plane of the girdle is oblique, sloping posteroventrally 15°. It is dis-
placed distally half its width and is without distal overlap. The precingular
ridge is formed by the projecting epitheca which flares but little. There is no
postcingular projection. The furrow is represented by the incurved surface
below the overhanging epitheca.

The sulcus is narrow, short, and sinuous, reaching only a bit beyond the
postcingular-antapical suture. It is only two girdle widths in length.

The plates are sometimes only very faintly outlined. In another lorica
(Figure 79) narrow intercalary bands were developed on the epitheca and wide
ones on the hypotheca, with the result that there was less overhang of the epitheca
in this lorica than in others. The anterior intercalary 1" is quadrangular, verg-
ing on squarish, and fills nearly 0.33 of the left anterior arc of the epitheca. Post-
cingular 7" ' is pentagonal, narrowing with a concave right facet within the

SYSTEMATIC ACCOUNT 115

girdle. The surface is very unlike, in different loricae, in degree and extent of
reticulations. These are of the pattern in H. gesticulatum, but in some loricae
are very lightly developed. In one instance all the plates except the three en-
tirely smooth apicals were faintly reticulated. In another loiica in ventral
view the only reticulated plates were two precingulars (1", 6"), the girdle plates,
and two postcingulars (1" ', 2" ')• All other plates on this face were without
reticulations, though porulate. In still another theca (Figure 83) on the dorsal
face only, were the precingulars (2", 3", 4", 5") and postcingulars (3" ', 4" ', 5" ')
reticulated. In general the reticulations are lighter when present and less uni-
formly developed over the theca than in other species of the gesticulatum group.

The cell contents are unknown.

Dimensions: — Six specimens measured. Length 130 (122-140), /jl, trans-
diameter 72.5 (67-76), m; length of right antapical 48.2 (42-55), m; of left 44
(40-48), M.

Variation : — Heterodinium extremum is quite variable in the depth of the
precingular constriction of the epitheca; in the overhang of the epitheca; in the
lateral extension and amount of posterior curvature of the sinistral lobe; in the
deflection of the apical pore upon the ventral surface; in the spread, obliciuity,
length, and width of the antapicals; and in the number and location of the plates
which are reticulated and the degree of reticulation. The development of the
intercalary zones modifies the proportions.

Comparisons: — As its specific name indicates this species exhibits extreme
conditions of asymmetry, having a longer, more recurved sinistral lobe than in
H. gesticulatum, H. mediocre, H. deformatum, or H. varicaior. The hypotheca is
shorter than in H. mediocre and the antapicals attain the maximum length in
the group. The postindentation is quite like that of H. gesticulatum, but deeper,
and its outline is modified by the asymmetrical narrowing in the distal part of
the right antapical, a character peculiar to this species only, and useful in dis-
tinguishing it from the closely related H. gesticulatum. The nearer approach to
equality of the antapicals in H. extremum also distinguishes it from H. gesticu-
latum.

Synonymy: — Described as forma extrema of H. gesticulatum by Kofoid
(1907a), but raised to specific status here because of clearly marked characters
consistently present.

The type locality is Station 4699 in the Easter Island Eddy.

Occurrence: — Heterodinium extremum is recorded (Plate 14) at six of the
127 stations with a total of eight specimens. There are 0, 0, 2, 3, 1, and 0 sta-

116 THE DINOFLAGELLATA

tions on the six lines, respectively, of the Expedition. Of these six stations, four
(4687, 4701, 4707, 4737) are in the South Equatorial Drift and two (4691, 4699)
in the Easter Island Eddy. All records are from hauls from 300-0 fathoms.

The temperature range at these six stations at the surface was 72°-75° and
the average was 74.4°.

The frequency at Station 4699 was 3% and less than 1% at all others.

Heterodinium varicator sp. nov.
Plate 16, fig. 39; Plate 20, fig. 06-72

Diagnosis: — A large, stout, quite asymmetrical species with very little
constriction of the anteriorly rounded, posteriorly squarish epitheca, and slight
overhang beyond the hypotheca; length, 1.50-2.15 transdiameters; hypotheca
longer, with less protuberant, often broadly roimded sinistral lobe, with or with-
out a denticle; antapicals long, much deflected to the right, generally subequal,
distance between tips more than 0.66 transdiameter ; postindentation broadly
concave, asymmetrical; surface reticulations variable in degree and extent.
Length, 125-155 m- Rare in the South Equatorial Drift and Easter Island Eddy
of the Eastern Tropical Pacific.

Description: — This stout species has a high degree of asymmetry mainly in
the hypotheca, caused by the larger mass in the sinistral lobe and by the extreme
dextral deflection of the antapicals. The epitheca, on the other hand, is less
modified and more symmetrical than the hypotheca. In ventral view the epi-
theca and h>T3otheca are equal in length, but in dorsal view, owing to the obliquity
of the plane of the girdle, the epitheca is only 0.50-0.57 of the length of the hypo-
theca. In one specimen (Figure 66) from Station 4681 the epitheca was more
nearly equal to (0.93) the hypotheca. The epitheca is subsemicircular, slightly
subangular (Figures 64, 65), or flattened (Figure 67), or even asymmetrical, with
the apical region inclined to the left. In its basal half the lateral margins become
nearly vertical and there is only a trace of precingular constriction, often a bit
more on the left than on the right side. The epitheca overhangs the hypotheca
about 0.50 a girdle width on the left and 0.75 on the right. The midventral
suture is slightly angled (150°) and the ventral area is large, elongated subtriangu-
lar, with centrally located, rounded, reniform ventral pore. The apical pore is
deflected ventrally below the margin and a trifle to the right.

The hypotheca is excavated midventrally and its width at the postcingular
margin is 0.80-0.85 that of the epitheca at the precingular margin. Its right

SYSTEMATIC ACCOUNT 117

margin is deeply concave, deepest below the postcingular-antapical suture, and
the left is asymmetrically convex with a massive sinistral lobe, generally broadly
rounded, sometimes bluntly pointed, and only in one instance with a denticle
above the postcingular antapical suture. The postmargin is an asymmetrical,
subsemicircular, broadly concave arc, deepest at the left, its depth varying from
0.38 to 1.67 of the distance between the tips of the antapicals. Its margin is
produced by a coarsely and irregularly dentate fin, often better developed at the
right.

The antapicals are subequal, both incurved, pointed, and subconical. The
right is the smaller, 20°-25°, but somewhat longer, about 0.6 transdiameter in
length, and deflected dextrally 30°-53° from the vertical. The left extends
farther posteriorly, is shorter, rarely a little more than 0.5 transdiameter in length,
stouter, 30°-50°, and has less dextral deflection (10°-30°). The distance be-
tween the tips is 0.60-0.65 transdiameter.

The plane of the girdle is deflected ventroposteriorly about 20°. Its width
is about 0.14 transdiameter, is subject to minor inequalities on the dorsal side,
and widens in the distal fjuadrant. It is without overhang and is displaced dis-
tally less than 0.5 girdle width. The precingular margin is an overhanging ledge
without lateral projection. There is no postcingular ledge. Its furrow is un-
equally developed, concave anteriorly, and flattening out posteriorly and dis-
tally.

The sulcus is short, its length being about 0.75 the distance from the pre-
cingular ledge to the postmargin. It is oblique, of equal width throughout,
slightly sinuous, and devoid of lists.

The plates are distinctly outlined by narrow suture lines. The anterior
intercalary lies wholly on the dorsal side, is quadrangular, and considerably larger
than the adjacent precingular 2". Its lateral margin almost fills the second
quarter of the left margin of the epitheca. Postcingular 7" ' is short and wide.
The suture between the postcingulars and antapicals on the dorsal side is very
oblique. Wide intercalary zones with fine secondary reticulations were found
between the postcingulars in one very large specimen. The surface is very un-
evenly and often irregularly reticulated. In some individuals the reticulations
on the entire surface are very faint. In the large specimen above referred to, the
pre- and postcingulars were finely reticulated and the apicals and antapicals
coarsely reticulated.

The cell contents are unknown.

Dimensions: — Seven specimens measured. Length, 139 (125-155) /n;

118 THE DINOFLAGELLATA

transdiameter, 78.4 (68-90) n; length of right antapical, 45.7 (35-48) fi; of left,
35.7 (25-45) m-

Variation: — Heterodinium varicator shows the greatest variation in the
hypotheca, especially in the breadth and mass of the sinistral lobe and in the
degree of emergence of a point and a denticle on its end. The obliquity of the
antapicals and the accompanying modification in the outline of the postindenta-
tion is also quite variable. One specimen (Plate 20, fig. 68) is so divergent that
it is tentatively included here as forma distortum f . nov. It is characterized by
marked inequality of the much deflected antapicals, wide, shallow postindenta-
tion, very broadly rounded sinistral lobe, and an asymmetrical epitheca with the
apex deflected to the left and the girdle sloping posterodextrally.

Comparisons: — This is the most divergent member of the subgenus Platy-
dinium. It is the most asymmetrical and has the most deflection of the antapi-
cals, but has a less protuberant sinistral lobe. Its postindentation is widest and
most nearly semicircidar. Its antapicals are longer and more oblique than in
H. mediocre and H. deformaium and have a wider postindentation than in H. ex-
tremum.

The type locality is Station 4699 in the Easter Island Eddy.

Occurrence: — Heterodinium varicator is recorded (Plate 14) at five of the 127
stations with a total of seven specimens. There are 0, 0, 2, 2, 1, and 0 stations
on the six lines of the Expedition. Of these five stations, two (4691, 4699) are
in the Easter Island Eddy, and three (4681, 4705, 4734) are in the South Equa-
torial Drift. No specimens were taken in surface hauls. It was taken in a haul
from 800-0 fathoms at Station 4681, and at the other four stations in hauls from
300-0 fathoms.

The temperature range at the five stations at the surface was 68°-81° and
the average was 73.8°.

The frequency was less than 1% at all stations.

The species is eupelagic, eurythermal, and is restricted to the deeper levels.

Heterodinium scotti sp. nov.
Plate 16, fig. 40; Plate 22, fig. 85

"Peridinean," Wilson E. A., in Scott, R. F. "The Voyage of the 'Discovery,'" 1905, vol. 2, plate facing p.
192. See our Plate 22, fig. 85.

Diagnosis: — A much elongated and apparently very large species, with an
extreme amount of asymmetry; length 2.4 transdiameters ; girdle displaced 1.3
girdle widths; epitheca with precingular constriction more anterior on the left

SYSTEMATIC ACCOUNT 119

side; length of the hypothcca 1.68 that of the epitheca; sinistral lobe elongated,
recurved, pointed; no denticles at postcingular-antapical suture; antapicals sub-
equal, a transdiameter in length, very slender, tapering; postmargin rounded,
oblique; postindentation almost the girdle width in depth. Length, 140-160 /x
(?). Probably from the tropical Atlantic.

Description: — Body greatly elongated, the length being 2.4 transdiameters.
The epitheca is disproportionately small, being only 0.6 that of the hypotheca.
Its length is 0.96 transdiameter. The apical region is slightly asymmetrically
rounded, somewhat flattened, but almost semicircular in outline. There are un-
usually deep, precingular lateral constrictions, as deep and wide as the girdle
itself on the left, and a less abrupt but exceptionally deep one on the right, a girdle
width posterior to the one on the left. The midventral suture appears to be very
oblique, deflected about 33° to the right. The suture lines, as drawn by Wilson,
leave room for a large ventral area, supplied by conjecture in dotted lines in
Plate 22, fig. 85.

The hjTJotheca is much foreshortened in the section of the midbody and is
withdrawn on the right side somewhat more than a girdle width, with resulting
wide overhang of the epitheca. Its left side is developed in a very large, pro-
tuberant sinistral lobe, with a sharp-pointed, strongly recurved, posteriorly
directed projection. There are no denticles whatever at the postcingular-
antapical suture.

The antapicals are remarkably symmetrical, incurved distally, very slen-
der, and taper to a sharp point. Their length is about one transdiameter and
both are deflected to the right about 20°-30°. The distance between their tips
is 0.8 transdiameter. The postmargin is asymmetrically rounded and deepest
at the middle.

The girdle is exceptionally well developed, as figured by Wilson, having both
pre- and postcingular ridges sharply projecting in horizontal ledges. There is
some reduction in the distal quadrant of the postcingular. The girdle has a dis-
tal displacement of 1.3 girdle widths. This is more than in any other species
in the genus.

The sulcus is evidently very short, scarcely equaling the displaced distal
end of the girdle.

The plates appear to be normal. In the reproduction in Plate 22, fig. 85 an
interpretation of the suture lines is made which brings Wilson's figure in harmony
with the plates in other species. It appears that he must have drawn not only
the ventral, but also some of the dorsal, sutures, as though they were on the ven-

120 THE DINOFLAGELLATA

tral face of the epitheca. The probable location of the ventral area is blocked
out in fine dots in our reconstructed figure and the lines interpreted as dorsal
sutures are drawn in dashes. The probable locations of the sulcus and post-
cingular 7' " are also dotted in our reconstruction. His original figure is repro-
duced without the modifications in our Figure 85. The features brought out by
this interpretation are the extreme obliquity of the midventral suture, the very
large size of the anterior intercalary 1* shown by its dextromedian border, the
very small postcingular 7' ", and the unusual anterior extension of antapical 1' ".

Dimensions: — Since no magnifications are given for Wilson's figure, its
size can only be conjectured. If it is of the same order of magnitude at the girdle
as other species of the gesticulatum group, its length is about 140-160 n.

Comparisons: — Heterodinium scotti differs from all other members of the
gesticulatum group in the relatively small epitheca; the extreme displacement of
the girdle; the inequality of level of the lateral constrictions of the epitheca on
the left and on the right side; the considerable obliquity of the midventral suture;
and especially in the size, elongation and curvature of the sinistral lobe and the
compensatory deflection of the apical region to the right. The elongation and
tapering form of the antapicals is not even approached in any other species of
Heterodinium.

Synonyvnj: — In Captain R. F. Scott's "Voyage of the 'Discovery'" (1905)
vol. 2, Mr. E. A. Wilson figures, on the plate facing p. 192, among his "Peridin-
eans caught on the voyage out" along with a Phalacroma and an Ornithocercus,
this species, which we here name in honor of the renowned explorer of the Ant-
arctic. This is the first species of the genus Heterodinium to have been figured,
thovigh not named by discoverer. Dr. Wilson.

The only type locality that can be assigned to this species, and that ques-
tionably, is the tropical Atlantic.

Distribution: — Heterodinium scotti is clearly tropical in its habitus, as in-
dicated by its elongated antapicals and sinistral lobe. Confirmation of this
appears in its association (?) with Phalacroma and Ornithocercus. The route of
the "Discovery" on the way out traversed the tropical Atlantic, but no other
tropical regions, so it is quite certain that this species came from the tropical
Atlantic.

SYSTEMATIC ACCOUNT 121

DoLiCHODiNiuM gen. nov.

Helerodinium Kofoid & Michener, 1911, parliin, p. 285, as H. lineatum; see also Helerodinium.

Diagnosis: — Body sub-biconical, subangular, elongated; without apical or
antapical horns; girdle submedian, spirally descending, widening at the distal
end; postcingular rim deficient; sulcus not indenting the epitheca; plate formula,
4', 0», 6", 6 (?), 6" ', 0", 3" "; postcingular 6" ' invading the distal end of the girdle;
wall porulate; fission line subvertical, passing through the apical pore.

Description: — The plate formula is the outstanding feature of this genus
and, in the absence of evidence of generic characters from other species than the
single one known, the description will be confined to a discussion of this character.
The plates are clearly defined by suture hues and, except in girdle series, have
been definitely analyzed. The apicals, l'-4', are subequal in length. Plates 1'
and 4' are on the ventral face and 2' and 3' on the dorsal. Plate 3' is connected
with the apical pore only by a somewhat narrowed anterior extension. There is
no anterior intercalary 1", but it is probable that apical 2' is derivable from 1" of
Heterodinium or vice versa.

This genus is created for a species placed tentatively by Kofoid and Michener
(1911) in the genus Heterodinium as an aberrant member. It is now separated
because (1) of differences in thecal structure, having in the epitheca four apicals,
l'-4', and no anterior intercalary 1"; the corresponding formula in Heterodinium
being 3' and l"; because (2) of the shifting of antapical 1" " into position distinctly
as a large postsulcal plate; because (3) there are six instead of seven postcingu-
lars; and finally and preeminently because (4) the theca is divided into right and
left moieties at binary fission, a phenomenon unknown in Heterodinium, by a
fission Une quite unique in the Peridinioidea in its reaching the apex. The sculp-
turing of the theca is also of a type found in no member of the genus Heterodin-
ium, and the general facies of this species, in addition to the individual charac-
ters above enumerated of morphological significance, would make it an odd figure
in that genus.

Comparisons: — The new genus is, however, closely allied to Heterodinium
and shows no such obvious affinities with any other genus. While the plate
formula differs in the particulars above noted from that of Heterodinium, the
two genera have several outstanding characteristic features in common, namely
the lack of a posterior girdle rim, the distal widening of the girdle, the thickening
of the lateral epithecal sutures, and the presence of a ventral pore at the angle
formed by the midventral suture with the apical-precingular suture on the ventral

122 THE DINOFLAGELLATA

face of the epitheca. There is, however, no indication of a differentiated ventral
area, such as occurs in Heterodinium, in connection with this pore in Dolichodin-
ium. The connections of apical 2' with the apical pore and its apical extension
are rather slight, as though it might be an intercalary 1> slipping anteriorly into
the apical series.

Synonymy: — The type and only known species is Dolichodinium lineatum
originally described by Kofoid and Michener (1911) as Heterodinium linealum.
The type locality is Station 4701.

Distribution: — Known only from the Easter Island Eddy and the South
Equatorial Drift of the Eastern Tropical Pacific.

Reproduction: — The specimen figured (Plate 12, fig. 6-8 and Plate 22, fig.
87, 88) is very evidently a recent schizont whose anterosinistral moiety of the theca
is from the parental source and the posterodextral but newly formed. This is
shown in the heavy, opaque structure with large elongated pores in the older part
and the deUcate, hyaline structure and small circular pores of the newer. The
bars along the suture lines are, in places, especially on the epitheca, much more
delicate in the newer wall than in the older, although on the ventral hj'potheca
(Plate 12, fig. 8) they are clearly thickened, especially distally.

The fission line has the morphological relations characteristic of this struc-
ture, at least in parting the theca into somewhat equal moieties along a line which
is at the most but slightly oblique, passing through, or near, the flagellar pore.
It differs from that in Ceratium in being less oblique and in reaching the apex
alongside the plate (apical 2') most hke the intercalary l-'of Heterodinium, which
in Dolichodinium is classed as an apical because it reaches the apex.

This fission line parts the sinistral plates as follows. On the ventral side in
passing posteriorly it parts apicals 1' and 4', precingulars 1" and 6", postcingu-
lars 1" ', and 7" ', antapicals 1" " and 2" ", and postcingular 7" ' from antapical
1" ". It also goes through or alongside the flagellar pore and sulcus. On the
dorsal side it parts apicals 1' and 3', precingulars 2" and 3", postcingulars 3" and
4", and postcingular 2" from antapical 1" ". The pores in older and newer parts
of the thecal wall are proportional in number and in distribution, but difTer in
character. In the newer part they are circular or sUghtly ellipsoidal, while in
the older part they are elongated in the direction of the meridian to as much as
threefold their transdiameter, and tend to show squarish ends. There is noth-
ing in pattern to suggest the reticulations which are so characteristic of the genus
Heterodinium which DoUchodinium resembles in girdle, sulcus, and heavily
barred sutures.

SYSTEMATIC ACCOUNT 123

DoLicHODiNiUM LiNEATUM (Kofoid and Michener)
Plate 12, fig. 6-8; Plate 17, fig. 41; Plate 22, fig. 87, 88

Heterodinium linealum Kofoid & Michener, 1911, p. 285.

Diagnosis: — A small species with sub-biconical, elongated, slightly poly-
hedral body; length, 1.5 transdiameters; without horns or spines; girdle sub-
median, displaced its width, without postcingular ridge; sulcus narrow near the
girdle, widening posteriorly; postcingular 7" ' elongated, equal to 1" '; surface
with longitudinal rows of elongated pores. Length, 58 n. Rare in the Eastern
Tropical Pacific in the Easter Island Eddy and the South Equatorial Drift.

Description: — In this small species the body is sub-biconical and rather
angular, especially in the hypotheca, elongated to a length of 1.5 transdiameters,
and circular at the girdle which divides it equally and horizontally. Horns and
spines are not developed. The epitheca is subconical (about 70°), having shghtly
convex lateral margins, more nearly straight dorsal and ventral faces, and flares
a little at the precingular rim. The apex is obliquely truncated. The apical
pore is very large, being over 0.5 girdle width across, and asymmetrically ex-
tended dextroventrally.

The hypotheca is more angular than the epitheca, subconical (60°), and more
sloping on the right than on the left. The antapex is very obliquely flattened at
an angle of 45°, sloping from the dorsal side ventrally.

The girdle is median, horizontal, and displaced its proximal width at the
distal end. Its anterior rim is a heavy projecting shelf without list, which over-
hangs the shallow furrow at right angles. Its posterior rim is developed. The
girdle widens distally to a width almost three times that of the proximal end.
The furrow is impressed a bit immediately under the precingular shelf. There
is no overlap.

The sulcus is a deep, very narrow groove extending only 0.4 of the distance
from the postcingular level to the antapex. The flagellar pore is a minute open-
ing at the level of the postcingular margin. The postsulcal area, however, is
widened out in a manner recalling the same structure in Gonyaulax and is not
trough-like as in Heterodinium.

The plate formula is 4', 0% 6", 6 (?), 6" ', 0^, 3" ". The apicals are subequal
plates, two ventral and two dorsal, with thickened lateral sutures. Of the six
precingulars, 1" and 6" are the largest, the others being confined to the dorsal
face. Postcingular 1" ' is a small, quadangular plate. Postcingular 7" ' is
pushed up into the distal end of the girdle as in some species of Heterodinium.

124 THE DINOFLAGELLATA

It is irregularly hexangular, but rounded posteriorly. The remaining postcingu-
lars are large and more or less equal. The three antapical plates are relatively
small. Plate 1" " is the pentangular postsulcal plate. Plate 2" " is on the left
side and 3" " is obliquely dorsal. The sutures about plate 3" " are heavy ridges,
ribbed on the postmargin, and in places developing spines at junctions of the
sutures. The plates are marked by numerous large pores, about five across each
postcingular at the girdle, which are remarkable in being elongated in the direc-
tion of the meridian to as much as threefold their transdiameter and arranged
rather obscurely in longitudinal lines. They tend to have squarish ends. There
is nothing in the pattern to suggest the reticulations which are so characteristic
of Heterodinium. In the specimen figured on Plate 12 the pores in the newer
half are very small and not much elongated. There are seventeen pores across
the dorsal face anterior to the girdle and eight between girdle and apex. A single
row only occurs in the girdle.

In one individual observed in life at Station 4097 the plasma was very hya-
line and there was a single, small, greenish-yellow chromosphere on the right side
at the end of the girdle.

Dimensions: — Two specimens measured. Length, 58-75 n; transdiameter,
40-45 m; width of girdle, 5-6 m; length of pores, 4 /n.

The type locaUty is Station 4701 in the South Equatorial Drift.

Occurrence: — Dolichodinium lineaium is recorded (Figure 41) at only two
of the 127 stations. Both are on the fourth line of the Expedition. One (4697)
is in the Easter Island Eddy and one (4701) is in the South Equatorial Drift.
Both are in hauls from 300-0 fathoms.

'The temperatures at the surface at the two stations were 72° and 75° and
the average was 73.5°.

The frequency at each station was less than 1%. Dolichodinium lineaium
is eupelagic, and confined to the deeper levels.

III. DISTRIBUTION OF THE HETERO-

DINIDAE AT THE STATIONS OF

THE EXPEDITION

The following is the record of the genera and species of the Heterodinidae
noted by us as the result of examinations, often repeated, of the plankton catches
at the various stations of the Expedition.

With each station number we have given the appropriate data including the
temperature at the surface in degrees Fahrenheit. Fuller data will be found in
the record of stations in Alexander Agassiz's (1906) report of the Expedition.

The occurrences of species at the stations are recorded according to the
catch under "Surface" and "300-0 fathoms to the surface," etc. At nearly all
stations collections have been made with both No. 12 and No. 20 silk nets. The
records of species in the two collections have been combined in a single list. The
differences between the two catches lie mainly in the greater proportional loss of
the smaller species in the No. 12 net with the coarser mesh. This, together with
the fact that the No. 20 catches were more thoroughly examined than those from
the No. 12 nets, has made the lists of species from the former somewhat the
longer. Since the No. 20 collection generally contained all of the species found
in the No. 12 and in larger numbers, there is no change resulting from this com-
bination of the records, except a few instances of additional species from the No.
12, or of larger numbers of individuals of species common to both collections. It
follows from this that the sum of the percentages of all species of dinoflagellates
at some stations is slightly in excess of 100. This, however, does not appear in
these lists since these present only the Heterodinidae.

No Heterodinidae were taken at 66, or 52% of the 127 stations at which
dinoflagellates were collected on the Expedition and not a single species was found
in Salpa stomachs.

Distribution by Stations
All records of temperature refer to the surface; P = frequency of less than
1%.

4580
Lat. 24° 55' N., long. 112° 45' W. October 10, 1904. Temperature, 76°.
300 fathoms to surface: — Heterodinium rigdenae, P; H. scrippsi, 1%.

126 THE DINOFLAGELLATA

4583
Lat. 22° 45' N., long. 110° 5' W. October 11, 1904. Temperature, 83°.
Surface: — H. calvum, P; H. milneri, P.
300 fathoms to surface: — H. curvaium, P; H. rigdenae, P; H. whittingae, P.

4587
Lat. 24° 42' N., long. 107° 25' W. October 12, 1904. Temperature, 82°.
100 fathoms to surface: — H. glohosum, P.
300 fathoms to surface : — H. curvaium, P.

4590
Lat. 18° 50' N., long. 104° 50' W. October 13, 1904. Temperature, 82°-83°.
Surface: — H. curvaium, P; H. glohosum, P.
300 fathoms to surface: — H. doma, P.

4694
Lat. 17° 20' N., long. 101° 32' W. October 14, 1904. Temperature, 84°.
300 fathoms to surface: — H. curvaium, P; H. gesliculatum, P; H. murrayi, P.

4596

Lat. 16° 47' N., long. 100° 27' W. October 14, 1904. Temperature, 84°.
Surface: — H. blackmani, P.

4604

Lat. 12° 21' N., long. 92° 13' W. October 17, 1904. Temperature, 84°.
Surface : — H. glohosum, P.

4606

Lat. 12° 21' N., long. 92° 13' W. October 17, 1905. Temperature, 85°.
300 fathoms to surface: — H. hindmarchii, P.

4609
Lat. 11° 05' N., long. 89° 35' W. October 18, 1904. Temperature, 81°.
300 fathoms to surface: — H. hindmarchii, P.

4613
Lat. 9° 45' N., long. 86° 20' W. October 19, 1904. Temperature, 80°.
300 fathoms to surface: — H. rigdenae, P.

4634
Lat. 4° 35' N., long. 83° 32' W. November 4, 1904. Temperature, 80°.
300 fathoms to surface: — H. gesliculatum, P; H. whiltingae, 2%.

4637

Lat. 1° 31' N., long. 86° 32' W. November 5, 1904. Temperature, 76°.
300 fathoms to surface: — H. expansum, P; H. laeve, P; H. mediocre, P;
H. rigdenae, P; H. scrippsi, P.

DISTRIBUTION 127

4638
Lat. 0° 27' N., long. 87° 13' W. November 6, 1904. Temperature, 75°.
300 fathoms to surface: — H. obesum, P; H. rigdenae, P; H. sinistrum, P;
H. whittingae, P.

4647
Lat. 4° 33' S., long. 87° 42' W. November 9, 1904. Temperature, 70°.
800 fathoms to surface : — H. rigdenae, P.

4648

Lat. 4° 43' S., long. 87° 7' W. November 9, 1904. Temperature, 71°.
300 fathoms to surface: — H. whittingae, P.

4650

Lat. 5° 22' S., long. 84° 39' W. November 10, 1904. Temperature, 71°.
300 fathoms to surface: — H. fenestratum, P; H. rigdenae, P.

4657

Lat. 7° 12' S., long. 84° 9' W. November 13, 1904. Temperature, 69°.
300 fathoms to surface: — H. agassizi, 1%.

4659

Lat. 8° 54' S., long. 86° 5' W. November 14, 1904. Temperature, 69°.
300 fathoms to surface: — H. fenestratum, P; H. rigdenae, P.

4664

Lat. 11° 30' S., long. 87° 19' W. November 17, 1904. Temperature, 68°.
300 fathoms to surface : — H. rigdenae, P.

4667

Lat. 11° 59' S., long. 83° 40' W. November 18, 1904. Temperature, 68°.
300 fathoms to surface : — H. murrayi, P.

4669

Lat. 12° 12' S., long. 80° 25' W. November 19, 1904. Temperature, 67°.
Surface: — H. fenestratum, P.

4670

Lat. 12° 8' S., long. 79° 2' W. November 20, 1904. Temperature, 66°.
800 fathoms to surface: — H. fenestratum, P; H. murrayi, P.

4676

Lat. 14° 28' S., long. 81° 24' W. December 5, 1904. Temperature, 69°.
300 fathoms to surface: — H. fenestratum, P; H. gJobosum, P; H. milneri, 1%.

4679

Lat. 17° 26' S., long. 86° 46' W. December 7, 1904. Temperature, 69°.

300 fathoms to surface: — H. curvatum, P; H. dispar, P; H. elongatum, P;
H. fenestratum, P; H. gesticulatum, P; H. globosum, P; H. milneri, P; H. murrayi,
P.

128 THE DINOFLAGELLATA

4680
Lat. 17° 55' S., long. 87° 42' W. December 7, 1904. Temperature, 68°.
Surface: — H. curvatum, P; H. mUneri, P.

4681

Lat. 18° 47' S., long. 89° 26' W. December 8, 1904. Temperature, 68°.

300 fathoms to surface: — H. agassizi, P; H.fenestratum, P; H. gesticulatum,
P; H. scrippsi, P.

800 fathoms to surface: — H. elongahim, P; H. gesticulatum, P; H. milneri,
P; H. obesum, 1%; H. varicator, P.

4683

Lat. 20° 2' S., long. 91° 52' W. December 9, 1904. Temperature, 70°.

300 fathoms to surface: — H. dispar, 1%; H. gesticulatum, P; H. milneri, P;

H. whittingae, P.

4686

Lat. 21° 36' S., long. 94° 56' W. December 10, 1904. Temperature, 72°.

300 fathoms to surface: — H. dispar, 1%; H. milneri, P.

4686

Lat. 22° 2' S., long. 95° 52' W. December 10, 1904. Temperature, 71°.
Surface: — H. milneri, P.

4687
Lat. 22° 49' S., long. 97° 30' W. December 11, 1904. Temperature, 73°.
300 fathoms to surface: — H. curvatum, P; H. extremum, P; H. gesticulatum,

4688

Lat. 23° 17' S., long. 98° 37' W. December 11, 1904. Temperature, 72°.

Surface: — H. curvatum, P.

4689

Lat. 24° 5' S., long. 100° 20' W. December 12, 1904. Temperature, 72°.

300 fathoms to surface: — H. gesticulatum, 1%; H. laeve, P; H. mediocre,

1%.

800 fathoms to surface: — H. gesticulatum, 1%; H. globosum, P; H. milneri,

P; H. whittingae, P.

4691

Lat. 25° 27' S., long. 103° 29' W. December 13, 1904. Temperature, 73°.

300 fathoms to surface: — H. agassizi, P; H. angulatum, P; H. asynimetricum,
P; H. blackmani, P; H. calvum, P; H. curvatum, P; H. dispar, P; H. extremum, P;
H. gesticulatum, P; H. globosum, 1%; H. hindmarchii, P; H. laeve, P; H. rigdenae,
P; H. scrippsi, P; H. varicator, P; H. whittingae, 1%.

4692

Lat. 28° 40' S., long. 104° 1' W. December 13, 1904. Temperature, 73°.
Surface: — H. curvatum, 3%; H. dispar, 1%; H. globosum, 1%.

DISTRIBUTION 129

4696

Lat. 25° 22' S., long. 107° 45' W. December 23, 1904. Temperature, 74°.

300 fathoms to surface: — H. calvum, P; H. dispar, 1%; H. doma, P; H.
gesticulatmn, P; H. hindmarchii, P; H. laeve, P; H. rigdenae, 1%; H. scrippsi, P;
H. spiniferum, P.

4697

Lat. 23° 24' S., long. 106° 2' W. December 24, 1904. Temperature, 75°.

300 fathoms to surface: — H. blackmani, P; H. curvatum, P; H. doma, P;
H. gesticulatmn, 1%; H. glohosum, P; H. hindmarchii, P; H. laeve, P; H. laticinc-
tum, P; H. leiorhynchum, P; H. milneri, P; H. mintilum, P; H. rigdenae, P; //.
sa-ippsi, P; Dolichodinium lineatum, P.

4698
Lat. 22° 50' S., long. 105° 31' W. December 24, 1904. Temperature, 75°.
Surface: — Heterodinium curvatum, 2%.

4699

Lat. 21° 39' S., long. 104° 29' W. December 25, 1904. Temperature, 75°.

300 fathoms to surface: — H. agassizi, P; H. asymmetricum, P; H. blackmani,
P; H. curvatum, P; H. dispar, P; H. doma, P; H. extremum, 3%; H. gesticulatmn,
P; H. glohosum, P; H. hindmarchii, P; H. laeve, 1%; H. mediocre, P; H. milneri,
P; H. rigdenae, P; ^. superhum, P; //. varicator, P.

4700

Lat. 20° 28' S., long. 103° 26' W. December 25, 1904. Temperature, 74°.
Surface: — H. curvatum, 1%.

4701

Lat. 19° 11' S., long. 102° 24' W. December 26, 1904. Temperature, 72°.

300 fathoms to surface: — H. agassizi, P; H. asymmetricum, P; H. hlackmani,
P; H. curvatum, P; H. dispar, 1%; H. doma, P; H. elongatum, P; H. expansmn, P;
H. extremum, P; H. gesticulatum, P; H. glohosum, P; i7. hindmarchii, P; i/. Zae»e,
P; H. mediocre, P; //. minutum, P; i/. obesum, P; //. rigdenae, P; //. scrippsi, P;
H. whittingae, 1%; Dolichodinium lineatum, P.

800 fathoms to surface: — Heterodinium laeve, P; //. inediocre, P; //. it'/iiY-

4705

Lat. 15° 5' S., long. 99° 19' W. December 28, 1904. Temperature, 72°.
300 fathoms to surface: — H. blackmani, P; H. curvatum, P; H. dispar, P;
H.fenestratmn, P; H. gesticulatum, P; //. milneri, P; //. varicator, P.

4706

Lat. 14° 18' S., long. 98° 45' W. December 28, 1904. Temperature, 72°.
Surface: — H. blackmani, P.

130 THE DINOFLAGELLATA

4707
Lat. 12° 33' S., long. 97° 42' W. December 29, 1904. Temperature, 72°.
300 fathoms to surface: — H. blackmani, 1%; H. extremum, P; H. fides, P;
H. viilneri, P.

4709
Lat. 10° 15' S., long. 95° 40' W. December 30, 1904. Temperature, 72°.
300 fathoms to surface : — H. agassizi, P ; H. fenestralum, P ; H. whittingae, P.

4711
Lat. 7° 47' S., long. 94° 5' W. December 31, 1904. Temperature, 75°.
300 fathoms to surface: — H. fenestralum, P; H. milneri, P.

4713

Lat. 5° 35' S., long. 92° 21' W. January 1, 1905. Temperature, 73°.
300 fathoms to surface: — H. dispar, P; H. expansum, P.

4715

Lat. 2° 40' S., long. 90° 19' W. January 2, 1905. Temperature, 75°.
300 fathoms to surface: — H. asymmetricum , P; H. mediocre, 1%, H. rig-
denae, P; H. whittingae, 1%.

4717
Lat. 5° 10' S., long. 98° 56' W. January 13, 1905. Temperature, 75°.
300 fathoms to surface: — H. rigdenae P; H. whittingae, P.

4719

Lat. 6° 28' S., long. 101° 16' W. January 14, 1905. Temperature, 75°.
300 fathoms to surface : — H. hindmarchii, P.

4721

Lat. 8° 7' S., long. 104° 10' W. January 15, 1905. Temperature, 75°.
300 fathoms to surface: — H. calvum, P; H. fenestralum, P.

4722

Lat. 9° 31' S., long. 106° 30' W. January 16, 1905. Temperature, 75°.

300 fathoms to surface: — H. dispar, P; H. fenestralum, P; H. milneri, P;
H. murrayi, P.

4724

Lat. 11° 13' S., long. 109° 39' W. January 17, 1905. Temperature, 79°.

300 fathoms to surface: — H. calmim, P; H. dispar, P; H. elongalum, P;
H. fides, P; H. gesticulatum, P; H. globosum, P; H. hindmarchii, P; H. lalicincium,
P; H. -milneri, P; H. minulum, P; H. murrayi, P.

800 fathoms to surface: — H. mediocre, P; H, milneri, 1%; H. rigdenae, 1%.

4728

Lat. 13° 47' S., long. 114° 21' W. January 19, 1905. Temperature, 77°.
300 fathoms to surface : — H. fides, P.

DISTRIBUTION 131

4730

Lat. 15° 7' S., long. 117° 1' W. January 20, 1905. Temperature, 79°.

300 fathoms to surface: — H. calvum, P; H. fenestratum, P; H. laeve, P; H.
obesum, P; H. rigdenae, P.

4732

Lat. 16° 32' S., long. 119° 59' W. January 21, 1905. Temperature, 79°.

300 fathoms to surface: — H. blackmani, P; H. dispar, P; H. elongatum, P;
H. fides, P; H. gesticulaiurn, P; H. laticinctum, P; H. milneri, P; H. obesum, P;
H. rigdenae, \%; H. scrippsi, P.

800 fathoms to surface: — H. rigdenae, P; H. scrippsi, P.

4734

Lat. 17° 36' S., long. 122° 35' W. January 22, 1905. Temperature, 81°.
300 fathoms to surface: — H. blackmani, P; H. cahum, P; H. deformatum, P;
H. elongatum, P; H. milneri, P; H. obesum, P; H. rigdenae, P; H. varicator, P.

4736

Lat. 19° 4' S., long. 125° 5' W. January 23, 1905. Temperature, 81°.

300 fathoms to surface: — H. deformatum, P; H. fides, P; H. scrippsi, P.

4737

Lat. 19° 57' S., long. 127° 20' W. January 24, 1905. Temperature, 81.5°.

100 fathoms to surface: — H. gesticulatum, P; H. globosum, P; H. hind-
marchii, P.

300 fathoms to surface: — H. agassizi, P; H. extremum, P; H. globosum, P;
H. laticinctum, P; H. rigdenae, 1%.

4739
Lat. 22° 11' S., long. 133° 21' W. January 26, 1905. Temperature, 79°.
300 fathoms to surface: — H. blackmani, P; H. calvum, P; H. curvatum, 1%;
H. laeve, P; H. laticinctum, P; H. rigdenae, P; H. scrippsi, P.

4740

Lat. 9° 2' S., long. 123°' 20' W. February 11, 1905. Temperature, 81°.

300 fathoms to surface: — H . fenestratum, P; H. globosum, P; H. milneri, P;
H. praetextum, P.

4742

Lat. 0° 3' S., long. 117° 15' W. February 15, 1905. Temperature, 77°.

300 fathoms to surface: — H. elongatum, P; H. fenestratum, P; H. mediocre,
1%; H. rigdenae, 1%.

BIBLIOGRAPHY

Agassiz, a.

1906. Reports on the scientific results of the Expedition to the Eastern Tropical Pacific,
in charge of Alexander Agassiz, by the U. S. Fish Commission Steamer " Albatross,"
from October, 1904, to March, 1905, Lieut.-Commander L. M. Garrett, U. S. N., com-
manding. V. General report of the Expedition. Mem. Mus. Comp. Zool. Harvard
College, 33, xiii + 75 pp., 96 pis., 8 figs, in text.

Blanchard, R.

1905. Regies Internationales de la nomenclature zoologique adoptees par les Congres
Internationaux de Zoologie (Paris, Redeval), 57 pp.

Cleve, p. T.

1900c. Notes on some Atlantic plankton-organisms. Kongl. Svensk. Veten. Akad.
Hand!., Stockholm, 34, no. 1, 22 pp., 8 pis.

Ehrenberg, C. G.

1S34. Dritter Beitrag zur Erkenntniss grosser Organization in der Richtung des kleinsten
Raumes. Abh. Akatl. AViss. Berlin, 1833, p. 145-336, pi. 1-11. Published separately
in 1834.

Entz, G., Jr.

1907. A Peridineak Szesvezeterol. Allattani Kozlemenyek, Budapest, 6, p. 11 30, 49-50,
pi. 2^.

1909. Ueber die Organizationsverhaltnisse einiger Peridineen. Math. u. Naturw. Ber.
Ungarn, 25, p. 246-274, pi. 811.

Hensen, V.

1911. Das Leben in Ozean nach Zahlungen seiner Bewohner. Uebersicht und Resultate
der quantitativen Untersuchungcn. Ergebn. Plankton-Exped. Humboldt-Stiftung, 5,
' 0, 402 pp., 1 pi., 67 figs, in text.

JORGENSEN, E.

1899b. Protophyten imd Protozoen im Plankton aus der norwegischen Westkuste.
Bergens Museums Aarbog, 1899, No. 6, 112 + Ixxxiii pp., 5 pis.

1911. Report of Prof. Dr. E. Jorgensen, of the Cathedral School of Bergen, Norway in
Mayer A. G., Ann. Rept. of the Director, Dept. of Marine Biol., Carnegie Inst, of
Washington for 1910, in Yearbook Carnegie Inst. Washington, 9, p. 146-148.

Karsten, G.

1906. Das Phytoplankton des Atlantischen Oceans nach dem Material der Deutschen
Tiefsee-Expedition 1898-1899. Wiss. Ergebn. d. Deutsch. Tiefsee-Exp. " Valdivia," 2,
pt. 2, no. 2, p. 137-219, pi. 20-34 (1-15).

1907. Das Indische Phytoplankton. Nach dem Material der Deutschen Tiefsee-Expedi-
tion 1898-1899. Wiss. Ergebn. d. Deutsch. Tiefsee-Exp. "Valdivia," 2, pt. 2, no. 3,
p. 221-548, pi. 35-54 (1-20).

KoFOID, C. A.

1906a. Dinoflagellata of the San Diego region. I. On Heterodinium, a new genus of the

Peridinidae. Univ. Calif. Publ. Zool., 2, p. 341-368, pi. 17-19, 2 figs, in te.xt.
1907a. Reports on the scientific results of the Expedition to the Eastern Tropical Pacific,
in charge of Alexander Agassiz, by the U. S. Fish Commission Steamer " Albatross,"
from October, 1904, to March, 1905, Lieut.-Commander L. M. Garrett, U. S. N.,
commanding. IX. New species of dinoflagellates. Bull. ISIus. Comp. Zool. Harvard
College, 50, p. 161-207, 17 pis., map.

134 THE DINOFLAGELLATA

191 lb. Dinoflagellata of the San Diego Region. IV. The genus Gonyaulax, with notes on
its skeletal morphology and a discussion of its generic and specific characters. Univ.
Calif. Pul)l. Zool., 8, p. 187-300, pi. 9-19, 5 figs, in text.

KOFOID, C. A., AND Mkhener, [E.] J. R.

1911. Reports on the scientific results of the Expedition to the Eastern Tropical Pacific,
in charge of Alexander Agassiz, by the U. S. Fish Commission Steamer " Albatross,"
from October, 1904, to March, 1905, Lieut.-Commander L. M. Garrett, U. S. N., com-
manding. XXII. New genera and species of dinoflagellates. Bull. Mus. Comp. Zool.
Harvard College, 54, p. 265-302.

KoFoiD, C. A., AND Skogsberg, T.

1928. Reports on the scientific results of the Expedition to the Eastern Tropical Pacific,
in charge of Alexander .\gassiz, by the U. S. Fish Commission Steamer " Albatross,"
from October, 1904, to March, 1905, Lieut.-Commander L. M. Garrett, U. S. N.,
commanding. XXXV. The Dinoflagellata: The Dinophysoidae. Mem. Mus. qf Comp.
Zool. Harvard College, 51, 7(36 pp., 31 pis., 103 figs, in text. '

LiNDEMANN, E.

1928. Peridineae (Dinoffagellatae) in Engler, A., Die Planzenfamilicn nebst ihren Gat-
tungen und wichtigeren Arten insbesondere den Nutzpflanzen. Ed. 2, 2, vi -{- 104 pp.,
92 figs, in text.

Murray, G., and Whitting, F. G.

1899. New Peridiniaceae from the Atlantic. Trans. Linn. Soc. London, Botany, ser. 2,
5, p. 321-342, pi. 27-33.

Ostenfeld, C. H., and Paulsen, O.

1904. Planktonprover fra Nord-Atlanterhavet (c. 58°-60° N. Br.), samlede i 1899 af Dr.
K. J. B. Steenstrup. Medd. om Gronland, 26, p. 139-210.

Pavillard, J.

1915b. Peridiniens nouveaux du Golfe du Lion. C. R. Soc. Biol., Paris, 78, p. 120-122,

1 fig. in text.
1916. Recherches sur les peridiniens du Golfe du Lion. Trav. Inst. Bot. Univ. Montpel-

Her, Serie mixte, Mem. 4, 77 pp., 3 pis., 15 figs, in text.

Schiller, J.

1916. Die neue Gattung Heterodinium in der Adria. Arch. f. Prot., 36, p. 209-214, 4 figs,
in text.

Scott, R. F.

1905. The voyage of the "Discovery" (London, Smith, Elder & Co.), 2, xii -f 508
pp., 107 pis., 2 maps.

Stein, F. R. von

1883. Der Organismus der Infusionsthiere nach eigenen Forschungen in systematischer
Reihenfolge bearbeitet. HI. Abth. II. Halfte. Die Naturgeschichte der arthrodelen
Flagellaten (Leipzig, Engebnann). 30 pp., 25 pis.

Wilson, E. A.

1905. Peridineans caught on the voyage out in Scott, R. F. The voyage of the "Dis-
covery," 2, plate facing p. 192.

INDEX

Page

Bibliography 133

dispar group 58

Dolichodinium, gen. nov 120

comparisons 121

description of 121

diagnosis 120

distribution and reproduction 122

synonymy 122

Dolichodinium lineatum (Kofoid and

Michener) 122

Euheterodinium Kofoid 47

e.rpa7i^uin group 48

gesticulatuvi group 102

Heterodiniidae, family, distribution of

genera and species of 125

Heterodiniidae Lindemann 11

Heterodiniidae, valid species .... 22

Heterodinium Kofoid 12

adaptive characters 24

coincident distribution of species . 19

comparisons 28

diagnosis 12

geographical distribution of species 19

historical discussion 20

key to species 29

nomenclatural changes in ... . 23

occurrence 16

organology 12

relations 11

relationships among species ... 25

reproduction 16

valid species . . . . - 22

Helcrodinium Agassizi Hensen ... 86

Heterodinium agassizi Kofoid ... 86
Heterodinium angulatum Kofoid and

Michener 51

Heterodinium asymmetricum sp. nov. 97
Heterodinium blackmani (Murray and

Whitting) 74

Heterodinium calvum Kofoid ... 32

Heterodinium curvatum Kofoid . . 70

Heterodinium deformatum (Kofoid) . 107

Heterodinium dispar sp. nov 59

Page
Heterodinium donia (Murray and

Whitting) 30

Heterodinium elongatum Kofoid and

Michener 61

Heterodinium expansum Kofoid . . 49
Heterodinium extremum (Kofoid) 13

Heterodinium fenestratum Kofoid 54

Heterodinium fides Kofoid 90

Heterodinium gesticulafum forma de-

formata Kofoid 107

Heterodinium gcstieulatum forma

extrema 'Kofoid 113

Heterodinium gcstieulatum forma

mediocris Kofoid 102

Heterodinium gesticulatum forma typica

Kofoid 109

Heterodinium gesticulatum Kofoid 109

Heterodinium globosum Kofoid ... 45
Heterodinium hindmarchii forma

maculata Kofoid 68

Heterodinium hindmarchii (Murray

and Whitting) 66

Heterodinium Kofoid & Michener

partim 120

Heterodinium laeve Kofoid and Mich-
ener 100

Heterodinium laticinctum Kofoid , . 95
Heterodinium leiorhynchum (Murray

and Whitting) 64

Heterodinium lineatum Kofoid & Mich-
ener 122

Heterodinium longum Kofoid ... 78
Heterodinium mediocre (Kofoid) . . 102
Heterodinium milneri (Murray and

Whitting) 41

Heterodinium minutum Kofoid &

Michener 34

Heterodinium murrayi (Murray &

Whitting) 38

Heterodiniimi obcsum Kofoid ... 36
Heterodinium praetextum Kofoid . . 56
Heterodinium ridgunae, Karsten ... 78
Heterodinium rigdenae Kofoid ... 78

136

INDEX

Page

Heterodinium scotti sp. nov 118

Heterodinium scrippsi Kofoifl ... SI

Heterodinium sinistrum sp. nov. . . 105
Heterodinium spiniferum Kofoid and

Miehener 52

Heterodinium, subgenus, nom. subgen.

nov 47

Heterodinium superbum Kofoid . . 43

Heterodinium \arica tor sp. nov. 116

Heterodinium whittingae Kofoid . . 92

kofoidi group 30

minuium group 34

non Peridinium tripos Ehrenberg . . 38

pariUurdi group 86

I'i'ridimum arrolatum Karsten ... 81
Peridinium BInrktiian.i Murray &

Whitting 74

Page

Peridinium deniatum Hensen .... 95

Peridinium down Murray & Whitting 30
Peridinium Hindmarchii Murray &

Whitting 66

Peridinium Iciorhynehnm ^lurray &

Whitting 64

Peridinium milneri Murray & Whit-
ting 41

Peridinium. pulchrum Hensen .... 70

Peridinium tripos Murray & Whitting 38

Peridinium tristijlum Hensen .... 109

Peridinium renter Hensen 86

Platydinium Kofoid, subgenus ... 85

rigdenae grou]) 78

Sphaerodinium Kofoid, subgenus . . 29

EXPLANATION OF THE PLATES

PLATE 1

PLATE 1.

Heterodinium calimm Kofoid; type specimen, fig. 1-2, Station 4691 (300-0 fathoms); fig. 3,

Station 4739 (300-O fathoms).
Heterodinium minutum Kofoid and Michener; type specimen, fig 4, Station 4699 (300-0

fathoms); fig. 5-7, Station 4697 (300-0 fathoms).
Heterodinium doma (Murray and Whitting), fig. 8, 9, Station 4590 (300-0 fathoms).

Fig. 1. Heterodinium ccdviim Kofoid, dorsal view. X 1000.

Fig. 2. The same, ventral view. X 1000.

Fig. 3. The same, right lateral view. Pores drawn on three plates only. X 1000.

Fig. 4. Heterodinium minutum Kofoid and Michener, oblique dextroventral view.
X 1000.

Fig. 5. The same, ventral view. X 1000.

Fig. 6. The same, dorsal view. X 1000.

Fig. 7. The same, transverse optical section showing nucleus, chromospheres, pusules,

apical pore, and pores in the wall. X 1000.

Fig. 8. Hetrrodiniwn doma (Murray and Whitting), dorsal view. X 1000.

Fig. 9. The same, ventral view. X 1000.

MEM MUS COMP ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 1

J. R. Micnener, A. B. Streedam and M. Boyd, del.

HrulOTYPE CCRP. BOSTON

PLATE 2

PLATE 2.

Heterodinium murrayi Kofoid; fig. 1-3, Station 4722 (300-0 fathoms).
Heterodinium obesum Kofoid; type specimen, fig. 4-6, Station 4734 (300-0 fathoms).

Fig. 1. //f/('rodimw7« 7KMrrai/t Kofoid, ventral view. X 1400.

Fig. 2. The .same, dorsal view. X 1400.

Fig. 3. The same, cell contents showing three chromospheres, nucleus partly concealed,
and many acicular rhabdosomes in the peripheral cytoplasm and also in the cytoplasm ex-
truded through the apical pore. X 1400.

Fig. 4. Ilettrodinium obesum Kofoid, left lateral view. X 1400.

Fig. 5. The same, dorsal view. X 1400.

Fig. (>. The same, ventral view. X 1400.

MEM MUS. COMP ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 2

^^^

f^i^^

/:"-

''<:-\

J. R. Michener, A B Streedam, del.

M6LI0TYPE CORP. aOSTON

PLATE 3

PLATE 3.

Heterodinium milneri (Murray and Whitting); fig. 1-2, 4-5, Station 4734 (300-0 fathoms)

fig. 6, Station 4722 (300-0 fathoms).
Heterodinium murrayi Kofoid; fig. 3, Station 4722 (300-0 fathoms).

Fig. 1. Heierodinium milneri (Murray and Whitting), optical section of cell con-
tents, showing crowded, stout, rod-like, radially arranged, hyahne bodies, clustered chromo-
spheres, and ellipsoidal nucleus. X 1400.

Fig. 2. The same, left lateral view. X 1400.

Fig. 3. Heterodinium. murrayi Kofoid, left lateral \iew, showing intercalary bands,
reticulations omitted. X 1400.

Fig. 4. Heterodinium vdlneri (Murray and Whitting), dorsal view. X 1400.

Fig. 5. The same, ventral view. X 1400.

Fig. 6. The same, left lateral view of a different specimen from that in Figure 2. X 14(X).

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA, PLATE 3

^<S

V<2iOe)<s>

J. R. Michener, A. B Streedam and M Boyd, del.

HELIOTYPE CORP. BOSTON

PLATE 4

PLATE 4.

Helerodinium. globosum Kofoid; type specimen, fig. 1-3, Station 4699 (300-0 fathoms); fig. 4,

Station 4732 (300-<:) fathoms).
Heterodinium supcrbum. Kofoid; tj-pe specimen, fig. 5-7, Station 4699 (300-0 fathoms).

Fig. 1. Heterodinium globosum Kofoid, dorsal view. X 607.

Fig. 2. The same, left lateral view. X 607.

Fig. 3. The same, ventral view. X 607.

Fig. 4. The same, ventral view of a variant with greater inequality of antapicals, and
different apical and ventral pores. X 607.

Fig. 5. Heterodinium, supcrbum. Kofoid, dorsal view. X 1000.

Fig. 6. The same, left dorsolateral view. X 1000.

Fig. 7. The same, ventral view. X 1000.

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 4

\^^°^^,

J. R. Micnener, A, B. Streedain and M Boyd, del

HELIOTYPE CORP. BOSTON

PLATE 5

PLATE 5.

Hctcrodiniuiii scrippsi Kofoid; fig. 1, Station 4734 (300-0 fathoms).

Hdrwdiniuiu dinpar sp. nov.; type specimen, fig. 2, 3, Station 4083 (300-0 fathoms).

Hetcrodiniuin rigdcnar Kofoiii; fig. 4, Station 4737 (300-0 fathoms).

Hctr rod i Ilium rxjimisuin Kofoid; type specimen, fig. 5-7, Station 4C37 (300-0 fathoms).

Fig. 1. Hrtcivdiniuin scrijrp^i Kofoid, ventral view. X 850.

Fig. 2. H drrudinium dispar Kofoid, dorsal view. X 1400.

Fig. 3. The same, ventral view. X 1400.

Fig. 4. Ilrtcrodiiiium rigdcnae Kofoid, ventral view. Specimen with secondary reticula-
tions in intercalary zone prior to ecdysis. X 675.

Fig. 5. Ilrtcrodinium crpansum Kofoid, ventral view. X 850.

Fig. 6. The same, right lateral view, reticulations omitted. X 675.

Fig. 7. The same, dorsal view. X 850.

MEM- MUS, COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 5

J. R. Micnener, A B Streedam. de

HELIOTYPE CORP. BOSTON

PLATE 6

PLATE 6.

Heterodinium angulatum Kofoid and Michener; type specimen, fig. 1, 2, Station 4691 (300-0

fathoms).
Heterodiiiium curvatuni Kofoid; type specimen, fig. 3, Station 4699 (300-0 fathoms).
Heterodinium spiniferum Kofoid and Michener; type specimen, fig. 4-6, Station 4696 (300-0

fathoms).

Fig. 1. Heterodiriium angulatum Kofoid and Michener, dorsal view. X 1000.

Fig. 2. The same, right lateral view, reticulations omitted. X 1000.

Fig. 3. Hderodinium cunatuiit Kofoid, left lateral view, reticulations omitted. X 482

Fig. 4. Hderodinium spiniferum Kofoid and Michener, left lateral view, reticulations

omitted. X 1000.

Fig. 5. The same, dorsal view. X 1000.

Fig. 6. The same, ventral view. X 1000.

MEM. MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 6

i;33si^

, R. Michener, A. B Streedain, del

HfLIOTYPE CCflf. BOSTON

PLATE 7

PLATE 7.

Hrin-ddimuin frnr-flrdtuni Kdfoid; type specimen, fig. 1, 4-(3, Station 4730 (300-0 fathoms).
Heterodinium pradrxiuni Kofoid; type specimen, fig. 2, 3, Station 4740 (300-O fatlioms).

Fig. 1. Heterodinium fenestral II III Kofoid, left dorsolateral view, retic\dations omitted.
X 1000.

Fig. 2. UiicrodiiiiiiiH jiraiirxiiiiii Kofoid, ohlique sinistrovcntral view, reticulations
omitted. X 482.

Fig. 3. The same, ventral view. X 482.

Fig. 4. /feferof/im'wni /enea/m<?/m Kofoid, dorsal view. X 1000.

Fig. 5. The same, optical section of cell contents showing .subventral spherical nucleus,
ellipsoidal chromosphere, tubular structure connecting with the ventral pore, and large pusule
opening into the apical pore. X 482.

Fig. 6. The same, surface view of the ventral face. X 1000.

MEM MUS COMP. ZOOL.

KOFOID AND ADAMSON Dl NOFLAGELLATA. PLATE 7

'V.

^f#

J R. Micr.ener, A. B. Streedam and M. Boyd, del

HELIOTYPf ffiRP. 30ST0N

PLATE 8

PLATE 8.

Hdcrodinium. elongaium Kofoid and Michener; type specimen, fig. 1-2, Station 4724 (300-0

fathoms); fig. 3. Station 4732 (300-0 fathoms).
Heterodinium airvaium Kofoid; type specimen, fig. 4, 6, Station 4699 (300-0 fathoms).
Heterodinium hindmarchii (Murray and Whitting); fig. 5, 7, Station 4691 (300-0 fathoms).

Fig. 1. Ilctrrodiniuiii dongatum Kofoid and Michener, dorsal view. X 1400.

Fig. 2. The same, left lateral view, reticulations omitted. X 1400.

Fig. 3. The same, ventral view. X 1400.

Fig. 4. Heterodinium curratum Kofoid, left lateral view, reticulations omitted. X 440.

Fig. 5. Heterodinium hindmarchii (Murray and Whitting), dorsal view. X 850.

Fig. 6. Hderodinium curvatum Kofoid, oblique apical view, reticulations omitted.
X 440.

Fig. 7. Heterodinium hindmarchii (Murray and Whitting), ventral view. X 850.

MEM MUS. COMP. ZOOL

KOFOID AND ADAMSON. Dl NOFLAGELLATA, PLATE 8

--0^-:

mi'

J, R. Micnener, A. B. Streedam and M. Boyd, del

HELiOTYPE CORP, Boeitn

PLATE 9

PLATE 9.

Heterodinium blackmani (Murray and AVhitting); fig. 1, Station 4739 (300-0 fathoms);

fig. 2, 3, Station 4699 (300-0 fathoms); fig. 4, 7, Station 4724 (800-0 fathoms).
Heterodinium cunatum Kofoid; type specimen, fig. 5, 6, 8, Station 4699 (300-0 fathoms).

Fig. 1. Heterodinium blackmani (Murray and Whitting), dorsal view, reticulations
omitted. X 482.

Fig. 2. The same, first precingular plate, with platelet containing the ventral area and
ventral pore, attached. X 482.

Fig. 3. The same, sulcus and adjacent area. Postcingular plate 7" ' has an oblique
reticular bar crossing its surface. Station 4G99 (300-0 fathoms). X MS.

Fig. 4. The same, ventral view. X 482.

Fig. 5. Heterodinium curmtum Kofoid, right lateral view. X 482.

Fig. 6. The same, ventral view. X 482.

Fig. 7. Heterodinium blackmani (Murray and Whitting), sulcus and adjacent region.
X 1000.

Fig. 8. Heterodiniuvi cunatum Kofoid, dorsal view. X 482.

MEM. MUS, COMP. ZOOL

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 9

J. R. Micnener, A. B, SUeedam and M. Boyd, del

HELIOTYPE CORP. BOSTON

PLATE 10

PLATE 10.

Heterodinium asymmetricum sp. nov.; type specimen, fig. 1, 2, Station 4f)09 (300-0 fathoms).
Heterodinium lalinndum Kofoid; type specimen, fig. 3, Station 4724 (800-0 fathoms).
Heterodinium. agassizi Kofoid; type specimen, fig. 4-S, Station 4ti99 (300-0 fathoms).

Fig. 1. Heterodinium. asyinmetricum sp. nov., dorsal view. X 075.

Fig. 2. The same, right lateral view. X 075.

Fig. 3. Heterodinium latidnctum. Kofoid, dorsal view. X 075.

Fig. 4. Heterodinium agassizi Kofoid, region of ventral area with ventral pore. X 1400.

Fig. 5. The same, region of sulcus. X 1400.

Fig. 6. The same, dorsal view. X 675.

Fig. 7. The same, left lateral view. X 675.

Fig. 8. The same, ventral view. X 075.

MEM. MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 10

i<ji;^'i^f3(3ui-

l^af

lS?.«ll«^aO0„^i

^^nfit

L©

:^^e»i

J. R. Michener, A. B. Streedam and M. Boyd, del

HFLIOTYPE rOKP, BOSTON

PLATE 11

PLATE 11.

Hctcrodiidum lactic Kofoid and Miehener; type specimen, fig. 1, 3, 5, 7, Station 4739 (300-0

fathoms).
Hctrwdinium fides Kofoid; type specimen, fig. 2, 4, G, Station 4728 (300-0 fathoms).

Fig. 1. llctcrodinium Jarre Kofoid and IMichcner, right lateral \icw. X 675.

Fig. 2. Hctcrodinium fides Kofoid, \entral %iew. X 675.

Fig. 3. Ileterodinium. laeve Kofoid and Miehener, left lateral view. X 675.

Fig. 4. Ileterodinium fides Kofoid, right lateral view. X 675.

Fig. 5. Heterodiniuin lucre Kofoid and Alichener, ventral view. X 675.

Fig. 0. Ileterodinium fides Kofoid, left lateral view. X 675.

Fig. 7. Ileterodinium laeve Kofoid and Miehener, dorsal view. X 675.

MEM. MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 11

'•>.: ';■

•n^

J. R. Michener, A. B. Streedatn snd M. Boyd, del

HELIOTYPE CORP. e05TCN

PLATE 12

PLATE 12.

Hetewdinium gcsticulalwn Kofoid; type specimen, fig. 1-5, Station 4594 (300-0 fathoms).
Dolkhodimum linratum (Kofoid and Michener); type specimen, fig. 6-8, Station 4701
(300-0 fathoms).

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8

Ildcrodinium gcsticulaium (Kofoid), dorsal view. X 440.

The same, left lateral view. X 440.

The same, ventral view. X 440.

The same, ventral area. X 900.

The same, sulcus and adjacent regions. X 900.

Dolichodinium linmtum (Kofoid and Michener), left lateral view. X 1400.

The same, dorsal view. X 1400.

The same, ventral view. X 1400.

MEM. MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 12

sSJ

\>v

,cau--.

yS.

'c^^n

■9Q

If^r^

J. R. Wlicnener, A. B. Streedam, del.

MetiOTYPE CORP. aOSTPN

PLATE 13

PLATE 13.

Map of distribution of species of Heterodinium belonging to the subgenera Sphaerodinium
and Heterodinium. Species of Sphaerodinium are represented by solid lines, and species of
Heterodinium by dotted lines. All record stations are marked by circles on the lines of the
route. Solid circles indicate surface hauls ; open circles, vertical hauls ; open circles including
solid circles, vertical and surface hauls at the same station. The occurrences of the species
at the various stations are indicated by radii, the keys to which are to be found in the key
stars on the left side of the chart. The frequencies are indicated by Roman numerals at the
distal ends of the radii; these numerals should be read from the distal toward the proximal
end of the radius. Absence of Roman numerals indicates that the species were "present"
{i.e., frequency of less than 1%.)

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON Dl NOFLAGELLATA. PLATE 13

H6LIOTYPE COBP. BOSTON

PLATE 14

PLATE 14.

Map of distribution of species of Heterodiniuni belonging to the subgenus Platydinium.
See explanation of Plate 13 for explanation of symliols.

MEM MUS. COMP ZOOL.

KOFOID AND ADAMSON Dl NOFLAGELLATA, PLATE 14

Lun3u}3ujujAse-— ;; =— -mediocris

at
C

HELIOTvPc CORP. BOSTON

PLATE 15

PLATE 15.

Figures 1-25. — Species of the genus Heterodinium arranged in subgenera, Sphaerodin-
ium, Heterodinium, and Platydinium, and in species groups, all drawn in ventral view, except
as noted, and to the same magnification, namely, 200 diameters. In figures copied from other
authors, the probable positions of certain sutures between plates, are indicated by dotted lines.

Subgenus Sphaerodinium.

Kofoidi group.

Fig. 1. //. kofoidi Schiller (1916, fig. 2). .\driatic.

Fig. 2. //. sphncroidr.um Kofoid (lOOfia, pi. 3, fig. 15). San Diego.

Fig. 3. //. doma (Murray and Wliitting, 1S99) Kofoid (1906a). Station 4691.

Fig. 4. //. cahum Kofoid (1907a, pi. 7, fig. 43). Station 4739.

Minutum group.

Fig. 5. //. minutum. Kofoid and Michener (1911, p. 285). Station 4697.

Fig. 6. //. ohcsum. Kofoid (19d6a, pi. 8, fig. 50). Station 4734.

Fig. 7. //. murrayi Kofoid (1906a, p. 353). Station 4722.

Fig. 8. //. miliirri (IMurray and WhittiTiir, 1S99) Kofoid (1906). Station 4734.

Fig. 9. //. supcrhum Kofoid (1907a, jjI. S, fig. 49). Station 4699.

Fig. 10. //. globosum Kofoid (1907a, pi. S, fig. 51). Station 4699.

Subgenus Heterodinium.

Expansum group.

Fig. 11. //. cxpan.sii.m. Kofoid (1907a, pi. 6, fig. 36). Station 4637.

Fig. 12. //. o;?._(7)//rt/?<»( Kofoid and Michener (1911, p. 285). Station 4691. Dorsal view.

Fig. 13. //. spinifcrum Kofoid and Michener (1911, p. 286). Station 4695.

Fig. 14. Il.fmcstriilnm Kofoid (1907a, pi. 8, fig. 47). Station 47.30.

Fig. 15. //. praetextum Kofoid (1907a, pi. 7, fig. 41). Station 4740.

Rigdeiiac group.

Fig. 16. //. rigdcnac Kofoid (1906a, pi. 18, fig. 6). San Diego.

Fig. 17. //. crassipcs Schiller (1916, p. 210, fig. 1). Adriatic.

Fig. 18. H. scrippsi Kofoid (1906a, pi. 17, fig. 1). San Diego.

Fig. 19. H. irirostrc (Murray and Whitting, 1899, pi. 29, fig. 5). Kofoid (1906a).

Dispar group).

Fig. 20. H. dispar Kofoid and Adamson. Station 4683.

Fig. 21. //. dongntuiii Kofoid and Michener (1911, p. 284). Station 4732.

Fig. 22. H. Iciorhynchum (Murray and Wliitting, 1899) Kofoid (1906a). From Murray

and ^^■lutting, 1899, pi. 29, fig. 2a.
Fig. 23. //. hindmarchii (Murray and Whitting, 1899) Kofoid (1906a). Station 4689.
Fig. 24. H. curvatum Kofoid (1907a, pi. 8, fig. 48). Station 4699.
Fig. 25. //. hlackmani (Murray and Whitting, 1899) Kofoid (1906a). Station 4724.

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 15

HfUIOTYPE CC-SP. BOSTON

PLATE 16

PLATE 16.

Figures 26-40. — Species of the genus Heterodinium, subgenus Platydinium, arranged in
groups, all drawTi in ventral view, except as noted, and to the same magnification, namely, 200
diameters.

Subgenus Platydinium.

Patnllardi group.

Fig. 26. H. pavillardi Kofoid and Adamson. After Pavillard (1916, pi. 2, fig. 2). Gulf

of Lyons.
Fig. 27. H. agassizi Kofoid (1907a, pi. 6, fig. .35). Station 4699.
Fig. 2S. H.jidcs Kofoid (1907a, pi. 7, fig. 45). Station 4728.
Fig. 29. H. whUiingae Kofoid (1906a, pi. 19, fig. 11). California Current.
Fig. .30. //. latidncfum Kofoid (1907a, pi. 7, fig. 46). Station 4724.
Fig. 31. H. asymmdricum Kofoid and Adamson. Station 4701. Dorsal view.
Fig. 32. H. inaequale Kofoid (1906a, pi. 18, fig. 91). San Diego.
Fig. 33. H. laeve Kofoid and Michener (1911, p. 284). Station 4639.

Gesticulatum group.

Fig. 34. H. si.nistrum Kofoid and Adamson. Station 4638.
Fig. 35. H. deformalum Kofoid (1907a, pi. 8, fig. 40). Station 4724.
Fig. 36. //. mediocre Kofoid (1907a, pi. 6, fig. 39). Station 4724.
Fig. 37. //. gcstimlatum Kofoid (1907a, pi. 6, fig. 37). Station 4699.
Fig. 38. H. extremum Kofoid (1907a, pi. 8, fig. 38). Station 4699.
Fig. 39. //. varicator Kofoid and Adamson. Station 4699.

Fig. 40. H. scotti Kofoid and Adamson. After Wilson (1905) in Scott (1905, vol. 2,
plate facing p. 192).

MEM MUS. COMP. ZOOL,

KOFOID AND ADAMSON. Dl NOFLAGELLATA, PLATE 16

MELiOTYPt CCRP. 90STCN

PLATE 17

PLATE 17.

Fig. 41. Distribution of Ileterodin.ium curvatum (marked by circles) and Dulichodinium
lineatum (marked by squares). Large solid circles and squares indicate locations of stations
with records from vertical or intermediate hauls. Large open circles indicate locations of
stations with records from surface hauls. Small open circles mark locations of stations at
which these species were not found.

Figures 42-47. Heterodinmvi rigdencie Kofoid. X 500.

Fig. 42-44. Ventral views. Stations 4724, 4732, 4734, respectively (300-0 fathoms).
Fig. 45. Dorsal view of specimen with more of an apical horn and shorter antapical
than are normally present, tentatively referred to this species. Station 4742 (300-0 fathoms).
Fig. 46. Ventral view. Station 4638 (300-0 fathoms).
Fig. 47. Dorsal view. Station 4613 (300-0 fathoms).

Plates labelled as follows on Figures 42 and 45 : — apical plates, l'-3'; anterior intercalary
plate, 1*; precingular plates, l"-6"; postcingular plates, 1" '-7" '; antapical plates, 1" "-3" ".

MEM. MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 17

4" ^^'

fHANGA REVA

^ Tratk of An>olroi% m t904-t9OS

HELIOT-iCe CCRP. BOSTON

PLATE 18

PLATE 18.

Figures 48-51. Plates of H,-tcrodinium scrippsi Kofoid (1906a, pi. 17, fig. 1^). X 500.
From California Current, off San Diego.

Fig. 48.

Ventral view.

Fig. 49.

Dorsal view.

Fig. 50.

Oblique left lateral view.

Fig. 51.

Apical view.

Figs. 52-
oms).
Fig. 52.

-55. Plates of H eterodinit

Ventral view.

Fig. 53.

Left lateral view.

Fig. 54.

Dorsal view.

Fig. 55.

Right lateral view.

X 500. Station 4724 (300-0

Abbreviations: — ap. po., apical pore;/, po., flagellar pore;/ur., furrow; /. mitap. h., left
antapical horn; midv. sut., midventral suture; posiind., postindentation ; postm., postmargin;
postc. l, postcingular ledge; prcc. I., precingular ledge; r. aniap. h., right antapical horn; sul.,
sulcus; i'. ar., ventral area; i\ pu., ventral pore; girdle plates, 1-7; apical plates, l'-'3'; anterior
intercalary plate, 1*; precingular plates, l"-6"; postcingular plates, 1" '-7" '; antapical plates,

1 " "_<!" "

MEM. MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 18

ap.po.

midv. Jut.

prec. I. ..

postc. L:

postind

ap. po

r. antap. h.

postind. -i \^'- 1, antap. h-.

_ prec. I.
5/ fur.

■postc. I.

3"-

HfLIOlVPc CORP. BOSTCN

PLATE 19

PLATE 19.

Figs. 56-5S. Hetcrodinium fides Kofoid. X 500.
Fig. 56. Ventral view. Station 4fi.3S (.300-0 fathoms).
F"ig. 57. Left lateral view. Station 4728 (300-O fathoms).
Fig. 58. Dorsal view of the same.

Figs. 59-(i5. Ilctrrodinium mrdiocrr (Kofoid). X 675.

Fig. 59-61. Ventral views of different lorieae from Station 4742 (300-0 fathoms).
Fig. 62. Dorsal view. Station 4637 (.300-0 fathoms).
Fig. 63. Dorsal view. Station 4724 (300-0 fathoms).
Fig. 64. Ventral view. Station 4699 (300-0 fathoms).

Fig. 65. Dorsal view, outline of spherical nucleus dotted in. Station 4742 (.300-0
fathoms).

Plates labelled on ?'igures 59 and 63 as follows ; — apical plates, l'-3'; anterior inter-
calary plate, P; precingular plates, l"-6"; postcingular plates, 1"' -7"'; antapical plates,
1 " "_ Q" ^

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA PLATE 19

MELIOTyPE CORP. BOSTON

PLATE 20

Figs. 66-72. Heterodinium varicator Kofoid and Adamson. X 500.

Fig. 66. Dorsal view. Station 4691 (300-0 fathoms).

Fig. 07. Ventral view. Station 4699 (300-0 fathoms).

Fig. 68. Dorsal view of forma distortum Kofoid and Adamson. Station 4681 (SOO-0

fathoms).
Fig. 69. Dorsal view. Station 4734 (300-0 fathoms).
Fig. 70-72. Dorsal views. Stations 4705, 4734, 4691, respectively (300-0 fathoms).

Plates labelled on Figures 66 and 67 as follows: — apical plates, I'-S'; anterior inter-
calary plate, 1"; precingular plates, l"-6"; postcingular plates, \" '-""'; antapical plates,

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA, PLATE 20

HELIOTYF£ COfl^. eOfeTON

PLATE 21

PLATE 21.

Figs. 73-78. Species of Heterodinium related to //. gesficulatum. X 500.

Fig. 73. Heterodinium deformatum {Koioid),d(jTsii\\iew. Station 4720 (300-0 fathoms)

Fig. 74. Heterodinium mediocre (Kofoid), ventral view. Station 4689 (300-0 fathoms).

Fig. 75. Heterodinium deformatum (Kofoid), ventral view. Station 4724 (300-0 fathoms).

Fig. 76. Heterodinium deformatum (Kofoid), dorsal view. Station 4736 (300-0 fathoms).

Fig. 77. Heterodinium agassizi Kofoid, ventral view; hypotheca detached from girdle
at girdle-postcingular suture showing arrow-shaped process from postcingular 7' " running
towards flagellar pore. Station 4731 (.300-0 fathoms).

Fig. 78. Heterodinium sinistrum Kofoid and .Vdaiiison, \entral view. Station 4638
(300-0 fathoms).

Plates of //. deformatum are labelled on Figure 73 and of //. mediocre on Figure 74 as
follows: — apical plates, l'-3'; anterior intercalary plate, 1'^; precingular plates, l"-6"; post-
cingular plates, 1" '-7" '; antapical plates, 1" "-3" ".

Figs. 79-81. Heterodinium extremum (Kofoid). X 500.

Figs. 79, 80. Dorsal views. Stations 4699, 4707 (300-0 fathoms).

Fig. 81. Ventral view. Station 4699 (300-0 fathoms).

Plates labelled on Figures 80 and 81 as follows: — apical plates, l'-3'; anterior intercalary
plate, 1"; precingular plates, l"-6"; postcingular plates, 1" '-7" '; antapical plates, 1" "-3" ".

MEM MUS COMP. ZOOL.

KOFOID AND.ADAMSON. Dl NOFLAGELLATA. PLATE 21

H6LIOTYP£ COBP, BOKTCK

PLATE 22

PLATE 22.

Figs. 82-84. Heterodinium cxtremum (Kofoid). X 50().

Fig. 82. Ventral view. Station 4699 (300-0 fathoms).

Figs. 83, 84. Dorsal views. Stations 4691 and 4687 (300-0 fathoms).

Fig. 85. llt'h'wdininm scotti Kofoid and Atlamson. Wntral \ie\v, after a figure by
E. A. Wilson in Scott (1905, vol. 2, plate facing p. 192). In this figure all suture lines on the
ventral face are drawn as in Wilson's figure. Those which he drew as on the ventral face, but
which we interpret as dorsal, are represented by dashes. Sutures whose location we con-
jecture are dotted in, as in the sulcus, plate 7" ', and the ventral area.

Fig. 86. Heterodinium gcsiiculatum Kofoid. Ventral view. Station 4691 (300-0
fathoms). X 500.

Figs. 87, 88. Dolichodinium li7ieaimH (Kofoid and Michener), tj'pe specimen. Station
4701. X 1000.

Fig. 87. Ventral view.

Fig. 88. Dorsal view.

Abbreviations: ap. jjo., apical pore;//, pa., flagellar pore; gird., girdle; prcc. r., precingular
ridge; postc. r., postcingular ridge; suL, sulcus; v. po., ventral pore. Plates labelled as follows:
— girdle plates, 1-6; apical plates, 1 '-4'; precingular plates, 1 "-6"; postcingular plates, 1" '-
6" '; antapical plates, 1" "-3" ".

MEM MUS. COMP. ZOOL.

KOFOID AND ADAMSON. Dl NOFLAGELLATA. PLATE 22

O'ftf

HELIOTYPE GOBP. BOCTOh

PUBLK^ATIONS

OF THE

MUSEUM OF COMPARATIVE ZOOLOGY

AT HARVARD COLLEGE.

There have been pubhshed of the Bulletin Vols. I to LXV,
Vols. LXVII-LXXIV; of the Memoirs, Vols. I to LI.

Vol. LXVI, of the Bulletin, and Vols. LII and LIII of the
Memoirs, are now in course of publication.

A price list of the publicatiotis of the Museum will be sent on appli-
cation to the Director of the Musetim of Comparative Zoology, Cambridge,
Mass.

Date Due

a^st#M97;

Harvard MCZ LIbrar

3 2044 066 302 266

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