QE905

.H3

1913

Halle, T

Some remarks on the classification
of fossil plants

T. G. HALLE

SOME REMARKS ON THE CLASSIFICATION
OF FOSSIL PLANTS

P^ 'RIKTED FROM GEOLOGISKA FORENINGENS 1 STOCKHOLM FuRilAXDLlNGAR NOV. 1913)

-H3

GEOL. FUKEX. F»"»R1IANDL. 15(1 ;'..".. Iliift. •'.. Xov. 1 0 1 ii. '.Wu

Somo remarks on the classification of fossil plants.

By

T. G. I^ALLE.

(With Plates 0 and 10).

The dithcultit'S attending the determination of fossil plants
are due, to a Jarge extent, to the diiference in the principles
adopted by different writers in the delimitation of species.
(Jne of the most important points of dispute is whether, in
doubtful cases, a broad or a narrow delimitation of species
should be preferred. In a recent paper ^ I have advocated a
narrow classification as being less apt to cause confusion in
nomenclature and hasty conclusions in geological and palaeo-
geographical matters. This course has later been criticized
by Professor A. C. Seward ^ in his review of the paper men-
tioned. In addition to his general reflections on the princip-
les, Professor Seward has also made several interesting re-
marks on the determinations of the Antarctic material. These
remarks, which are closely connected with the general stand-
point of Prof. Sewaud, call for an explanation from myself;
and it would appear, too, that some points in my discussion
of the principles would need emphasizing. It is naturally
hopeless to attempt a reconciliation of the two opposite prin-
<'iples, and a continued abstract discussion would serve no

' Hallk. T. G. The Mesozoic Flora of (Jraham Land. Wissens<'h. Ergebn.
(). Srhwedisihen Siidpolar-Expcdition 1901—1903. Bd. 3, Lief. 14, Stockholm
1913.

- Seward. A. C An extinct Antarctir Hora. The New Phytologist. Vol.
12. Nos. 4 Sc f). London 1913.

368 T. G. HALLE. [Nov. 1913.

useful purpose, but a few of the points in question may
deserve some further consideration. i

After quoting my opinion 'that it is a lesser evil to keep j
forms separated which are identical than to identify such as
are distinct' Prof. Sewakd argues as an antithesis that it is
a sound general principle 'to keep the mind open when there
is no sufficient warrant for closing it'. It is a strange illu-
stration of the difference in the conception of the problem
that this very principle is the first and chief reason also for
the exactl}^ opposite course advocated by the present writer.
Indeed, I believe that a brief consideration of the process of
classification of fossil plants will show the narrow delimita-
tion of species to represent the less committing way.

The individual specimens constituting the material of the
palaeobotanist are grouped into species according to the degree
of morphological similarity — very much in the same manner as
in the classification of recent plants. There is the important
difference, however, that the palaeobotanical specimens, in the
overwhelming majority of cases, do not consist of individuals
but only of portions of such. Therefore different organs of
one individual may be referred to not only different species
but different genera, this being the rule in many groups. And
in cases of dimorphism, and even of great variation according
to position on the plant, different specimens of one and the
same kind of organ must often be described under different
specific names though they really belong to the same species.
These consequences, as every one knows, are unavoidable, being
with necessity connected with the nature of the palaeobota-
nical material. And they cannot be eliminated by means of
even the very broadest classification: there will always be
cases of dimorphism in which it is impossible to trace the
connection of the different t^^pes, and it is only exceptionally
that the material to be described is sufficiently large to give
a satisfactory idea of the range of variation of the species.
It follows, therefore, as a generally accepted fact, that the

i 1 :;.";. II. i;.] CLAssiFirvTiox of fossil plants. 309

jalaeobotanical species, especially in critical frnjujjs, is not a
taxononiical unit in llic same sense as species in the recent
flora. The fact of two groups of forms being described under
different names does not imply, therefore, that they are ne-
cessarily distinct species but only that tliey cannot at pre-
sent be ]) roved to be identical. And this, it must be
re])eat('(l. holds true even in the case of a broad classification.
The process of classification of fossil plant- remains, in other
words, must naturally be, on the whole, a synthetic one. It
consists in grouping together specimens into form-units (arti-
ficial species) and piecing together such different parts and
variations of a plant which have been described as artificial
species, in order to get as accurate an idea as possible of the
whole plant and its variations (the natural species). The
writer who prefers in a dou])tful case to regard two similar
forms as different species therefore only confesses his inability
to establisl^ an identification at the moment. He cautiousl}*
makes a pause in the synthetical process just because he
believes it to be a sound principle 'to keep the mind o])en
when there is no sufficient warrant for closing it'.

The fact that the palaeobotanical species cannot be acce])ted
as necessarily coinciding w4th the taxonomical may be used
and has been used also as an argument for a broad classifica-
tion. Since it is hopeless to strive at a natural delimitation of
the species in all cases, it may be as well, it is argued, to use
the specific name in a liberal sense, as a designation for a
certain general ty])e of the organ in question. In referring a
questionable form to a certain palaeobotanical species, it is
said, the former has not been stated actually to belong to
the same natural species but only to show a certain resem-
blance of form. — This way of reasoning raises the (|uestion:
'what's in a name?' It cannot l)e helped that the palaeo-
botanical species to a large extent is treated as a natural
one. An observation made on one or some few specimens of
a ])alaeobotanical species is generally and naturalU' regarded

37U T. G. HALLE. [Nov. 1913.

as applicable to the whole species. Palaeobotany in general
is, indeed, dependent on the possibility of so nsing, with all
possible precaution, the palaeobotanical species, and the em-
])loyment of specific designations mainly serves just to mark
utf such units. It is clear, therefore, that it must be an im-
perative demand to make these units as pure and unmixed
as possible, so that a statement made in regard to some spe-
cimens of the species may with the greatest possible proba-
bility apply to all others designated by the same name. An
example may serve to illustrate the dangers w^hich, from this
point of view, attend a broad classification. We may imagine J
two sets of specimens of fern-leaves, which an adherent of h
narrow classification would prefer to treat as two species but
which, with a liberal delimitation of the species, are regarded
as one. Specimens of the first of these sets are later found
to have sporangia of, for instance, Osmundaceous type, and
the result will be that the whole species will be stated to
belong to that group. If then, after some time, specimens of;
the second set are found to belong to stems showing the ana-^
tomieal features of the Marattiales, this character, by still
regarding the species as a unit, will probably be applied to
the species as a whole. The simple explanation may be that
the name is used for two different natural species which may
well belong to quite different groups. — It is clearly imposs-
ible to guard satisfactorily against this risk, even with a
narrow delimitation of species, and no doubt a large group
of mistakes in palaeobotany is of this nature. But the use
of specific names in a narrow sense will naturally tend to
lessen this risk, whereas it hardly brings any other danger
instead of it. In the case quoted, a mistake in this direction
would only mean that the process of reconstruction of the.
particular species is delayed.

However one may look at the problem, it would appear that
the use of specific names in a restricted sense would be less apt to
cause confusion and mistakes. The most conspicuous objection,

r.< I :•..'.. II. f.. CLAPSIl rCATlON (iK FOSSIL I'l^ANTS. 371

iind the (nic most often exj)r»'sse(l, is that this cniirsf imolves
the creation of lari^^e niunhers of transient speeitic names,
due onh' to the mistakes' of the respective authors. Havini;
r^'gard to thr limited nature of the i)alaeobotanical material,
it nf'»'(l hardly be feared that the mere nunilM-r of names will
cause serious troubles. And there is this very important
<litterence between the two eases: that a laro^e number of
name-, which are bound each to a well-defined form, when
finally acknowledged as mere synon^'ms of a species brini;
murh less confusion than a much smaller number of others
which are used in a different sense by different authors and
have Ijeen applied each to different species. The splitting up
of a vaguely defined species will always be found much more
<lifficu]t than the joining of tw(t narrowly defined forms to
one species and the latter process only represents a natural
stage in the progress of the classification of fossil plant-remains.

The phytogeographical side of the question has been for
the present sufficiently considered in my paper on the Gra-
ham Land Flora, but it remains to add a few words in regard
to its bearings on the stratigraphy. The importance of not in <;
tliH exact geological horizon on which a certain form occurs
lia< been emphasized by Prof. Xathorst — who gives, more-
over, in his paper on the naming of dicotyledonous leaves* an
exposition of many of the most important precautions to be
considered in the classification of fossil plants. Kven a small
difference between two forms may be of importance if each
form is found to be restricted to a certain horizon. A closer
attenti<m to this question than is generally bestowed b\'
palaeol)otanists may often be found useful in the delimitation
of species, and, rice rcr.sa, may increase the geological impor-
tance of fossil plants. For this purpose, however, a narrow
and careful deliniital ion of species is of itaraniount im])ortance.

It is not intended to advocate, with the above remarks, an

' Xathorst. A. <J rdier die Hentnnung f<issil«T l»iki>tylonhlatter. Hota-
nisches Centraildatt. Vol. 2^). iMSfi.
\t^ — i:i022U. G. F. /•'. /!'/.y.

:\r2 T. (i. HALLE. [Nov. 11)13.

iiu restricted use of new specific names. The aim must always
be identification of those forms whose identity appears
probal)le, and there is no doubt that with the increase of
the material more and more 'species' will be found to be iden-
tical. Professor Seward, indeed, has clearly demonstrated,
how a large material makes it possible to recognize as mere
varieties forms which in case of a smaller number of speci-
mens no doubt would be described as different species —
linffordia Gocpperti of the AVealden-flora being a very good
instance. <)nly, it would appear that, when a less extensive
material has to be described, a narrow delimitation would
represent the more cautious course. The chief point is, of
course, that the material should be sufficient for a description.
It need not be large, since even a fairly small material may
often be valuable, but it must be distinct and it must be
well described and w^ell figured. If these demands are met
the species may be safely used as a basis for future discus-
sion and thus answers its purpose, even if it is ultimately
found to be a mere synonym.

After this abstract discussion the most important of Pro-
fessor Seward's remarks on the determinations of the Antarctic
plant-remains will be considered. These remarks, as already
mentioned, for the most part are closely connected with the
general standpoint of Professor Seward, and in such cases
need no other discussion than the general exposition given above.
The case of the only Eqnisetites-sjyecies of the Hope Bay
Flora may be mentioned, however, as a good illustration. The
close resemblance of some specimens of the Antarctic species
E. approxiniatiis Natii. to E. rajinalialensis Schimp. is noted
in my memoir, with the remark that both forms may be
identical. The Indian material of the species is very poor,
however, consisting only of diaphragms, short pieces of stems
and broken leaf-sheaths with teeth indistinct or wanting.^

^ The specimens in Feistmantei/s PI. 35, figs. 3, 4, are probably inverted.

IM 3.',. 11. tj.] CLASSIFICATIOX n|.- FnS.SH, I'LANTS. 378

The charactors displayed l)y this material are so vague that
they may well occur in many different species. The r^^sem-
hlance between some of the more impei't'eet specimens of leat*-
sheatiis from (-rrahani Land and tlie t'<|uall\- imperfect Indian
ones, therefore, does not seem suttieient to warrant the use nf
the name given to the latter: the identitication would he
l»ased chietly on the lack of characters in (jne of the forms,
in this case — which is worse — in the type-specimens. There
is undoubtt'dJv a very ffreat risk in extendino: a name siv^'u
to such imperfect specimens to a much bettei* characterized
form, as thereby the name, on very insufficient grounds, is
made to mean so much more than it has done originally and,
therefore, perhaps something fpiite different. The danger is
tliat forms from other parts of the world would probably be
identitied hy other authors with the Indian E. rajmaludensis
because of their resemblance not to the type-specimens but to
the Antarctic ones. And the true Indian E. rajmahaJrusis
may ultimately be found to l)e something different: this is, at
any rate, just as ])ossible as that it is identical with the
Antarctic form. The confusion arising then may be easily
imagined, whereas, if the two forms are temporarily kept
separate, an ultimate identification would l)ring no such con-
sequence.

Regarding the use of the generic name Schroptcris^ the reas-
ons have been set forth in my discussion of P(icl/yj>trrfs (1. c,
!». oD). To a reference of my S. f'nrcafa to the genus Dicho-
jifriis I must most strongly object. As types of Didiojiti ris
should be regarded the large Italian species for which Zigno
founded the genus. The difference, in regard to both shape
and venation of the pinnules, between Scbroptrfis f'nrcafa
and Dichopttris risianica Zkjno is so obvious as to need no
further explanation, and the coincidence in the forking of the
rachis cannot be regarded as being of any importance. If
Dirhoptrris is extended so as to embrace forms like Schro-
})trris f'urcata it would much sooner come to include the genus

374 T. (J. HALLE. [Nov. 1913.

Pachypti r'is. And as Fachi/pteris is the older name and has
been commonly used — also by Professor Seavard in the 'York-
shire Flora' — the name Dicliopteris should be rejected. The
only ])lan to retain the genus Bichopicris is evidently to em-
plo}' it in a very restricted sense for forms like those from
the Italian Oolite, in which case my species of ScJerojyteris
naturally cannot be included in it. Whether the venation
and the peculiar habit of the Italian forms are sufficiently
important characters to warrant this course, will not be dis-
cussed here, but it is certain that if Dicliopteris is used
in the sense of Prof. Seward's ^ it cannot be upheld but must
be rejected in favour of Facliyptcris. Whichever course be
followed, therefore. Dichopjfrris has only a secondary impor-
tance for the delimitation of the genera Pachypteris, Tlmui-
feldia and Sclcropteris. This is the reason why I did not consider
it in the discussion of these genera, judging it wiser to leave
this question to somebody who could make a thorough compara-
tive study of the Italian forms. — From what has been said above
regarding the relation of Pachyptteris and Dichopteris, it will
already be clear why P. dalmatica, which was probably cor-
rectly^ referred by v. Kerner to Pachypteris^ has not been in-
cluded in Dichopfcris.

The nomenclature of Zamitean fronds, on which Professor
Seward also remarks, is a very difficult matter, and as yet
there hardly exists any method of classification which is not
beset by difficulties. In my Grraham Land paper I have dis-
cussed the relations of the genera ZamiUs. Ptilopliyllum, and
Otozamites: and Professor Seward remarks that I have used
Zamites 'for several forms which agree much more closely
with Ptilophyllnm fronds than with Zamites as usually em-
ployed'. This remark is interesting as it shows that Profes-j
sor Seward accepts the generic name Ptilophyllam. If both'
Zamites and Ptilopliylluni are employed it is naturally neces-
sary to establish some agreement as to how the genera are

* Fossil Plants. Vol. 2, p. 552.

15(1 3o. II. •;.] CLASSIKrCATIOX nj' Ko-SIL I'LANTS. 375

to be delimited, in order that the nauit's may not he used
difterently l)y difterent writers. I have tried to chdimit Pfi-
lophylhtm by aceeptini^ Feistmantki/s definition which makes
the downward trend of both pinna-edges at the base the ge-
neric character. This is thus no new idea, the genus having
been accepted in this sense also by other palaeobotanists af-
ter the days of Feistmantel. This character, it must be ad-
mitted, is not a very opportune one, since it is often only
seen with difficult}-, and it does not mark off the genus very
distinctly from all forms of Zamifrs, yet it seems to l^e the
better one under the circumstances. As typical members of the
genus Za mites may be regarded the species with large fronds
of which the pinna-bases are distinctly rounded and characte-
rized by a more or less marked callosity, Z. gigas being the
best known representative of this group. The callosity can-
not always be observed, however, and its occurrence is gener-
ally not considered as a conditio sine qua non for a reference
to Zcunites. To the same genus are often referred smaller
forms without callosity and with the pinna-basis very slightly
rounded. As well-known representatives of this group of forms
may be regarded the species of Zamitcs described by Heer*
from Greenland; and it was because of the resemblance of the
Antarctic fronds to these Grreenland forms that I referred the
former to Zamites.

The difference between these two groups is in many cases
obvious, and I have considered it in the paper quoted by
distinguishing the two types as different sections of the ge-
nus, resp. Kuzaiiiitcs and Snhzaniitis. It may be that the
latter section would ])e better designated by a new generic
name, but I did not judge such a course sufficiently war-
ranted. If, on the other hand, the choice is between includ-
ing these forms in Zdiuitts and referring them to PtilojtlniJ-
turn, it would appear that the former genus is decidedly t(> be
preferred.

* Flora I'ossilis arrtica. Vol. 3, li>73, p. •;:', :ni.l lull . VU 11 ami 1.'..

37(^ T. G. IIALLE. [Nov. 1913.

It is true that VtUopliylhim as originally defined would em-
brace also fronds of the type in question. But, as in the case
of Zaniitcs and other old genera of C^^cadophytean fronds, it
has become necessar}^ to substitute a more distinct definition
for the original one: otherwise the genus would come into
collision with other genera now commonl}^ accepted. This
has been done by Feistmantel, whose definition of the genus
seems to meet the most important demand to be made on a
new definition of an old generic name, viz. to be based on the
specimens for which the name was created.^ AVith exception
of the numerous illustrations given by Feistmantel of the
Indian species of FtUophylhwi, very few forms of that genus
have been figured with due regard to the shape of the pinna-
bases. In addition to a reproduction (PL 9, fig. 1) of one of
Feistmaxtel's figures of Ftnophyllum aciitifoUum I have there-
fore given, in PL 9, figs. 2 — 5, some photographs, in twice the
natural size, of the pinna-bases of one of the English forms
of the genus. This form, which is one of those commonly
known among English palaeobotanists as Williamsonia pecten^
is identical with Cycaditcs pectinoides Phillips and should
be named Ftilophyllum pectinoides (Phill.) Morr. It is
seen from the figures to show the generic character of Ftilo-
phyllani in Feistmaxtel's sense by having an asymmetric
pinna-base with both edges decurrent on the rachis. And it
must be admitted that this is a very characteristic type of
pinna-base which well deserves to be distinguished from that
of typical Zamites species, such as Z. gigas.

In order to decide whether the Antarctic species of Zamites
should be retained in that genus as a somewhat less typical
group or included in PtiloplnjUnm, they should be compared
with typical specimens of these two genera. The text-figures

^ Regarding the relation of Feistmantel's definition to Morris' type-speci-
mens see Halle, T. Gr.: Some plant-bearing deposits in Patagonia and Tierra
del Fuego and their floras. K. Sv. Vet. Akad. Handl., Bd 51, N:o 3, 1913,
p. 36.

l!'l l'"'. II.'"..' (I.ASSri irATIO.N OF FOSSIL I'LANTS. 377

\'2 and lo, pp. r)7 and ')!!, res])., in my ^lesu/oic Flora of Gra-
liani Land, the illustrations given hy Hkkii (I. c; 1^1. 14; Pi.
1'), tigs. 1 — 10) and es])peially the photographs in I'l. 10. figs,
l-fi. of thr present paper may he regarded as showing the typi-
<al shape of the pinna-hase (»f the group in (lutstion. A (-(^m-
parison of these illustrations with those given in 1*1. !• of spe-
eirs of Ffiloplnillnm cannot fail to show the diffei'ence. It is
true that there may he many cases in which the distinctive
characters cannot he discerned <in account of tlie })reservation,
and also that intermediate forms exist; hut the same will be
found to be the case with every other classification of these
fronds. In a fairly large material of Vtilophylhnn pcctinoi-
<lrs from Whitby in Yorkshire I have found the generic charac-
ter - in Feistmantel's sense — to be present in all well
preserved specimens. It is possible that in the larger collec-
tions in English museums there may be transitional forms;
l)ut as the proportion may be taken to be the same, these
cannot l)e very numerous. — The same remark applies to the
si)ecimens of F. pecten from the Middle Estuarine series and
probably to the larger number of the forms referred, in Pro-
fes.sor Seward's Jurassic Flora of the Yorkshire Coast, to
WiUiamsoiid pecten, not, however, to Otozandtes (ioldiei Bkun.,
(as figured l)y Saporta 1N75), 0. Hislojii Feistm.. 0. aufinsti-
foiius Heer, etc., which arie regarded in the same work as
synonyms of Williaiusonia pecte}t, but which I should prefer
to retain in the genus Otozamites.

If forms like my Antarctic species of Zamites and the
Greenland fronds described by Heer under that name are re-
ferred to J*ftl()2)hi/lln)ii, the chief character of that genus as
defined by Fel^^tmaxtel could no longer l)e upheld. Instead
there would li<* included in the same genus forms with two
tvjjes of pinna-bases: the symmetrical base with slightly
rounded corners of m}' Suhzaiitifes-gvoui) and the asymmetri-
cal decurrent base of VtiloplujllmH in Feistmantel'.>< sense.
It would be difficult to find any sufficient generic character

o78 T. G. HALLE. [Nov. 1913.

of this wider genus Ftilophyllnni. From the typical Zamitcs
it would diifer mainly by the less marked rounding of the
basal corners and by the smaller size. The former distinction
may be available in some cases but it would only be a dif-
ference of degree, since even the very slightly rounded base of
some of the Antarctic Zamites-forms belongs to the same type
as that of Z. gigas and other typical species. If the speci-
mens figured in PL lU, fig. 7, of this paper are compared
with those in figures 1 — () of the same plate, which show
typical pinna-bases of different species, from Greenland and
(Iraham Land, referred by the present writer to Zamitcs^
it will be difficult to find any dift'erence sufficiently distinct
to be expressed in a diagnosis. Indeed, it is not impossible
that, w^ith the classification advocated by Professor Seward.
the specimens in PI. 10, fig. 7, might be referred by some
authors to Ptilopliijlliim. Yet this figure shows very typical
specimens of Zamites gigas: only, these are reduced to the
average size of the Ftiloj^hyUiim-fronds. It would appear
from a consideration of this figure that the more stringent
definition of Zamites is based to a great extent on the size.
A difference of size may be a character of some importance;
but it would not seem to be convenient to base on such a
distinction a separation of two form-genera of a kind of
fronds which show a rather great variation in size.

The choice is thus between distinguishing Zamites and Ftilo-
pliyllum in accordance with either the difference of shape of the
pinna-base or the difference in the degree of rounding of the
latter and in the size of the frond. As the latter course
would involve both a mixing of two types with a diff'erent
symmetry of the pinna-bases in one genus and a vaguer gene-
ric distinction between the genera, it does not appear to pre-
sent any advantages.

It remains to discuss the question of the classification of
sterile Coniferous shoots. I have created a new name, Elato-
cladus, to be used for such sterile shoots of Conifers, whether

IM ;;:>. 11. t"..' classification of fossii, im.ants. 37i>

of (lorsiventral or of radial habit, which cannot be included in
any of the c^encra instituted for more i)cciiliar forms. Pro-
fcs.sor Skwaiid, who admits tliat the nomendaturt' for these
forms needs revision, remarks on tlie ohjecti(jn against the name,
alread\' discussed in my paper, that this generic term -includes
forms with leav»\s (tf the Tcuitcs type as well as branches
with leaves like those of Siilienolepidium, Elatidcs^ and other
genera'. He proposes as an alternative plan 'to retain Taxitrs
ill the wide sense in which it is used by most authors for
twigs bearing linear and usually distichous leaves similar to
those of Taxus, certain species of Podocarpus, Sequoia .senqx r-
riirns, and other recent Conifers, and to adopt the name
]*'n/(02)Jn/Uu)H, for forms with radially disposed leaves like
those of Elatides, Sphcnolepidium, and Chcirolcpis' .

As to the use of Ta.iites for shoots of dorsiventral habit
(with pseudo- distichous leaves) there is nothing to be said
against this plan. Brongxiart instituted the genus for forms
with only a general resemblance in habit to the recent spe-
cies of Taxus. He employed it, however, especially for Ter-
tiary forms which ])ossibly might be compared with the re-
cent genus with greater probability than those from older forma-
tions. U this (juestion is considered alone, it would seem con-
venient to retain Taxitcs as advocated by Professor Seward;
and 1 at first intended to employ the name in this sense.

In regard to the other group, shoots with radial symmetr}^
the question is more difficult. To use Pagioplnillnm in a wide
sense, for this group, would not seem to l)e an imjtrovement.
Fa(/ioj)ht/llu))i is usually employed as designation for a fairly
natural form-genus, which undoubtedly should be retained for
forms with short and thick, often more "or less triangular and
strongly keeled leaves, the species figured by Saporta (Plau-
tes jurassiques. Vol. T), 1884, Pis. 4;")— o')), under the name of
FarJu/jtl/i/lhoH being good representatives of the group, in ad-
dition to the type-species, ra<jiopliijllum jicrrgrinum (LiNDL. &
HuTT.) ScuENK. It is true that there are transitions from this

o80 T. G. HALLE. [Nov. 1913.

type to others — an example of this is the specimen of my
Elatocladus hefcrojthylla figured in p. ^5, text-fig. 18 h, of my
Mesozoic Flora of Graham Land — but a definite separation of
form-genera of sterile Conifers cannot be hoped for. Fagio-
pltyUnm is thus hardly available as a designation for the
larger group, and it is difficult to find any other existing
name for this purpose. Elatides would appear to be more
appropriate than Tagiopltyllum, as the former genus represents
a more general type with a less specialized kind of leaves,
but since cone-bearing specimens of the genus have been de-
scribed it would appear to be better to reserve the name for
these. If no other existing name can be found for the group
in question, there remains the possibility of creating a
new one.

At first it seems no doubt to be the best to use two difi'er-
ent form-genera for the sterile shoots of, so to say, the com-
mon, non-specialized Coniferous habit, and I originally intend-
ed to accept this plan in the description of the Antarctic ma-
terial. In this material, however, as well as in most collect-
ions of any considerable number of fossil coniferous twigs,
there are numerous specimens regarding which it is impossible]
to say whether the habit is radial or dorsiventral, i. c, toJ
which of the two groups they should be referred. Moreover,'
there exist species which show both types in distinct develop-
ment on one and the same specimen. Such, for instance, is the
case with the dimorphic species described as Elatocladus hete-
rophylla, for which it would be difficult to find a suitable
place with the classification proposed by Professor Seward.
Naturally a classification should not be rejected because of
the existence of a single case of dimorphism, with types of
two form-genera in connection. But this kind of dimorphism
is not rare among the Conifers, and it is known also in other
fossil forms, for instance in Stachyotaxiis. In any case the
fact that the generic name Elatocladus 'includes forms with
leaves of the Taxites-iy]^^ as Avell as branches with leaves

IM ;;.'). If. i). CLASSIFICATION OF FOSSIL I'LANTS. 381

like those of Sji/nnoh /lii/imii, FJiitnhs, and (jIIkt guiuTci', caii-
iiut be re^j^arded m ijfso as an <)l)jection ai^ainst its usj*. It
is, on the contrarv, the casp that th«* actual occiirreuce in the
same specimens of Ixtth these types iui|dird the use of the
same name for Ixith of them. W'lien we take into consideraticjii
the further fact that the two ty[)es are by no means distinct
— the dorsiventrality of the yV/:ri7c.s-shoots ncjt being due to
the arrangement of the leaves on the shoots, which is onl\-
pseudo-distichous — there won hi apjjcar to l)e good reasons for
using only one name.

The most important objection against the use of Elatocladus
as I have proposed it, and one of which I am well aware, is
that it will have to include a large number of forms which
really may be very diiFerent. But this is due to the nature
of the material: when the latter does not show any sufficient
gaps in the series of variations to permit the separation of
dilt'erent form-genera, the best thing seems to l)e to give way
before this fact. The genus is in a high degree a provisio-
nal one and should be used only for forms which it is im-
possil)le to place in a better defined form-genus. Some such
form-genera already exist, and many more will no doubt have
t(j be distinguished in the future.

In bringing these remarks to a close it may be once more
emphasized that it is not intended to advocate that the deter-
i minations discussed here are necessarily right. All determi-
nations of impressions of fossil plants must naturally be
])rovisional and errors ai*e inevitable, whichever method id'
classification is adopted. Of this, however, there can be no
doubt, that the errors bring much less evil consecjuenees in
the way (d" confusion and uncertainty if, within reasonable
limits, the species are kept small and as strictly defined as
possible.

382 T. G. HALLE. [XOV. 1913.

Explanation of Plates.

PI. J>.

Fig. 1. Ptilophyllum acutifolium MORR. Reproduction, in natural
size, of the twice enlarged fig. 1 a, pi. 2. of Feistmantel:
Ueber die indischen Cycadeengattungen Ptilophijllum und
Dictyozaniites, 1876.

Figs. 2 — 5. Ptilophyllum pectinoides (PlllLL.) MORR. Portions of
fronds from the Lower Estuarine Series of the Inferior Oolite,
at Whitby, Yorkshire, showing the pinna-bases, X 2.

PI. 10.

Figs. 1—3. Zamites antarcticus Halle. from the Jurassic of Hope
Bay, Graham Land. Fig. 1, portion of the frond in text-
fig. 13 c of Halle : The Mesozoic Flora of Graham Land;
nat. size; tig. 2, two pinna-bases from the same specimen,
showing indications of callosity, X 5; fig. 3, jnnna-bases of
another specimen, x 5.

Fig. 4. Zamites pusillus Halle. Pinna-bases of the specimen in
PI. 7, fig. 12, and text-flg. 12 a of Halle : The Mesozoic
Flora of Graham Land, X 5.

Figs. 5, 6. Zamites hrevipennis Heer, from the Cretaceous of
Western Greenland, X 2^ 2. Fig. 5, part of the specimen
in PL 15, fig. 10; fig. 6. of the one in PI. 15, fig. 9, of
Heer: Die Kreide-Flora der arctischen Zone. Flora fossilis
arctica. Vol. 3.

Fig. 7. Zamites gigas (Lindl. & HuTT.) AIORR. Large slab with
several fronds from the Lover Estuarine series in the In-
ferior Oolite of Whitby in Yorkshire, reduced to ^ '4 of the
nat. size.

All the specimens figured, with exception of the reproduction in PL
1. fig. 1. are in the Palaeobotanical Department of the State Mu-
seum of Natural History at Stockholm.

Geol. Foren:s FOrhandl. Bd 35.

PI. 9.

CcderqulsU Graf. A.-U., Sthlm.

Gool. [-orciKS Fiirhandl. Bd 35
X5

/¥''''<

X 2 • li 6

X' 4

CeOerquisis tir;ii. A.-H , Mhlm.

Bolanicat Garden Libra

QE905.H3 1913

Hall Thore Gustaf/Some remarks on the c

gen

llilllllll

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