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Postilla

PEABODY MUSEUM OF NATURAL HISTORY

YALE UNIVERSITY
NEW HAVEN, CONNECTICUT, U.S.A.

Number 112 17 November 1967

A REAPPRAISAL OF THE NORTH AMERICAN SPECIES OF
THE SILURO-DEVONIAN TRILOBITE GENUS SCOTIELLA

J. H. SHERGOLD

DEPARTMENT OF GEOLOGY
UNIVERSITY OF NEWCASTLE UPON TYNE
NEWCASTLE UPON TYNE, ENGLAND*

ABSTRACT

The type material of Scotiella Delo 1935 is redescribed and
the generic diagnosis emended to include trilobites in which the
anterior and median lateral glabellar furrows are both strongly
and poorly defined. The genus now embraces the species Scotiella
logani (Hall 1860), S. conservatrix (McLearn 1924) new com-
bination, S$. minor (M’Coy 1851), S. samsonowiczi Tomcezykowa
1962b and S. opatowiensis Tomczykowa 1962b. Scotiella obsoleta
Ulrich and Delo 1940 is reclassified as Kloucekia (Kloucekia)
obsoleta new combination.

* Present address: Bureau of Mineral Resources, P.O. Box 378, Canberra
City, Australia.

ii)

Postilla YALE PEABODY MUSEUM No; 2

INTRODUCTION

The genus Scotiella Delo 1935 has a geographical distribution
which extends from Nova Scotia across the Atlantic to Poland.
It is of importance in that it has a limited stratigraphical range,
being confined to the passage beds between the Silurian and Devo-
nian Systems.

The species now referred to Scotiella show considerable varia-
tion in characteristics associated with the furrowing of the glabella
and pygidium and with the axial structures of the latter. These
variations have been incorporated into an emended generic
diagnosis.

Scotiella is closely related to Acastella Reed 1925, a genus
existing contemporaneously during the late Silurian and early
Devonian in northwest Europe. Scotiella is differentiated on the
character complex diagnosed below. Trends found in Scotiella,
but not in Acastella, include a tendency towards obsolescence of
the anterior glabellar furrowing and a mesial interruption of the
posterior axial rings of the pygidium. The similarities between
Scotiella and Acastella suggest a common ancestry which may be
found in Acaste Goldfuss 1843.

During the research necessary for this short paper I have had
the opportunity to study at first hand types and other specimens
from collections in the Peabody Museum of Natural History, Yale
University, New Haven, Connecticut; plaster casts of type speci-
mens from the collections of the Geological Survey of Canada,
Ottawa; material recently collected from the type section at Ari-
saig, Nova Scotia, by Professor A. J. Boucot, Division of Geo-
logical Sciences, California Institute of Technology, Pasadena,
California; and also material deposited in the collections of the
Geological Institute, Warsaw, from approximately contempora-
neous strata in Poland.

In the following text YPM indicates specimens from the col-
lections of the Peabody Museum of Natural History; GSC those
from the Geological Survey of Canada and USNM those from the
U.S. National Museum, Washington.

When referring to the morphogenesis of the species considered
the terms “early” and “late” holaspid are constantly mentioned.
These terms are applied to differentiate the smallest and largest
groups of holaspid instars. In the Acastinae and related trilobites

A REAPPRAISAL OF THE TRILOBITE Scotiella 3

the smallest (earliest) holaspides frequently possess genal and
caudal mucronations which may be resorbed during the succes-
sion of holaspid instars. The largest (latest) holaspides, the adults
oi the species, may be completely non-mucronate, e.g. the develop-
ment of Acastocephala macrops (Salter 1864) (see Shergold,
1966).

The species primarily concerned in this paper were originally
described by Hall (1860, pp. 156-7) as Dalmania logani and
referred to Dalmanitina logani (Hall) and D. logani (Hall) var.
conservatrix by McLearn (1918a, 1918b, 1924). The genus
Scotiella was erected by Delo (1935, p. 409) with Dalmania logani
(Hall) as the type species.

SYSTEMATIC DESCRIPTIONS

FAMILY DALMANITIDAE Vogdes 1890
SUBFAMILY ACASTINAE Delo 1935
GENUS SCOTIELLA Delo 1935

TYPE SPECIES. Dalmania logani Hail, 1860, p. 156, text-fig. 18.

OTHER SPECIES. Scotiella conservatrix (McLearn 1924) (McLearn,
1OSasp. 33; 1918b, p, 1295 1924. p: 1168; pl. XXVIL, figs: 1,2,
5). Scotiella samsonowiczi Tomezykowa 1962 (Tomcezykowa,
RS 62D; apps. 193-5, ply XOCXTV; figs. 1-6, pl. XXKV, ‘ig:- 2).
Scotiella opatowiensis Tomczykowa 1962 (Tomezykowa, 1962b,
Peel95-6) spl, XXXIV tess 7-95 pl, XXX, ‘figs, 1 3).
Scotiella minor (M’Coy 1851) (M’Coy, 1851, p. 161 and Sher-
gold, 1967, pl. 25, figs. 1-3). Scotiella cf. minor (M’Coy 1851)
(Shergold, 1967, pl. 24, figs. 9-11).

AGE. Late Silurian to early Devonian

DISTRIBUTION. North America: Nova Scotia, Arisaig coast sections
(Moydart Formation, Stonehouse Formation, zones a-c, common
in zone c). North West Europe: Poland, Holy Cross Mountains
(Rzepin Beds); United Kingdom, Westmorland (Kirkby Moor
Flags) and Priors Frome, Herefordshire (?Downtonian, basal
Rushall Beds).

EMENDED DIAGNOSIS. Scotiella is defined by an association of
characteristics some of which are shared with other Acastinae but

4 Postilla YALE PEABODY MUSEUM No: 112

which differ in degree. The following are deemed diagnostic:
glabellar furrows incised to varying depths, there being apparent
gradations between species with well-defined furrows and those in
which the anterior and median lateral furrows are faint or obso-
lescent; convexities of associated lateral side lobes correspondingly
variable; preoccipital lobes approximately one-fourth as wide
(exsagittal) as median lateral lobes; a narrow (transverse), up-
raised, longitudinal glabellar ridge flanked by shallow depressions
joining anterior lateral and preoccipital furrows always present
but varyingly distinct; long genal spines in young holaspides, short
spinules in adults; pygidium with five to six strongly furrowed
pleural segments, up to 11 axial rings; posterior axial rings may
be uniformly entire throughout morphogenesis or mesially inter-
rupted in the adults; margin entire in late holaspides, possibly
denticulate on the shell of early holaspides; short, delicate, often
inflected, caudal spinule, as in Acastella.

RELATIONSHIPS. in emending the diagnosis of Scotiella an attempt
has been made to bring the genus into direct comparison with
Acastella. It seems most closely related to those species of Acas-
fella, similar to A. spinosa (Salter 1864), the type species, which
have non-denticulate late holaspid pygidial margins. Species of
Scotiella may be readily distinguished from those of the Acastella
spinosa species-group by their longer glabellar furrows, reduced
preglabellar furrow and shorter genal mucronations.

Scotiella conservatrix (McLearn 1924) new combination
pli, fiesy 1-7, text-fig-

Dalmanitina logani var. conservatrix, n. var.; McLearn, 1918a,
p. 33 (nomen nudum).

Dalmanitina logani var. conservatrix, n. var.; McLearn, 1918b,
p. 129 (nomen nudum).

Dalmanitina logani var. conservatrix McLearn; McLearn, 1924,
p, 168, pl. XX VII, figs. 1 (YPM 472), 2 (GSC 5999).
Dalmanitina logani (Hall); McLearn, 1924, pl. XXVII, fig. 5
(GSC 5998).

Scotiella logani var. conservatrix (McLearn, 1918); Delo, 1940,
p. 34, pl. 2, figs. 18 (GSC 5999), 19 (YPM 472), non=figy 20
(proetid, YPM 25656).

A REAPPRAISAL OF THE TRILOBITE Scotiella

Scotiella logani conservatrix (McLearn); Tomezykowa, 1962b,
jay EP.

Cet OR ee ee
we - bes

Text-figure 1. Scotiella conservatrix (McLearn 1924) new combination 10.

TYPES. Lectotype: cephalon, YPM 472. Paratypes: cranidium,
GSC 5999; pygidium, GSC 5998.

DISTRIBUTION. Scotiella conservatrix (McLearn 1924) occurs in
the Moydart Formation, zone a, and in the Stonehouse Forma-
tion, zones a-c, of the Arisaig coast section, Nova Scotia. It is not
a common trilobite (McLearn, 1924, p. 20).

AGE. Siluro-Devonian passage beds, probably equivalent to marine
Downtonian. Copeland (1964, p. 7) has considered the age of
the Stonehouse Formation, on the basis of ostracod faunas, to be
post-Ludlovian, similar ostracods occurring in the Obere Oesel-

6 Postilla YALE PEABODY MUSEUM No. 112

Gruppe on the island of Oesel, previously assigned a Downtonian
age.

DIAGNOSIS. A species of Scotiella Delo 1935 with the following
characteristics: glabella moderately convex (sag.); three well-
defined pairs of lateral glabellar furrows, with a tendency for the
anterior lateral and preoccipital furrows to converge adaxially;
frontal-lobe anteriorly gently angled, with irregularly dispersed
tubercles; anterior and median lateral glabellar lobes gently con-
vex (tr. and sag.); preoccipital lobes one-fourth as wide (exsag. )
as the median lateral lobes, with stronger convexity (tr.); preg-
labellar furrow very narrow (sag.), barely present; very short
genal mucronations in the adult; pygidium with nine to ten axial
rings; rings 5-6 often with very low mesial tubercle; rings 6-10
(more usually 7-10) interrupted mesially; five pleural segments,
strongly furrowed; short, delicate caudal spine; border smooth,
moderately wide; margin entire in adults.

DESCRIPTION. Cephalic outline pentagonal, postero-laterally
rounded-truncate with short genal mucronations. Surface of frontal
lobe of glabella with irregular rows of tubercles.

Glabella strongly pentagonal in outline, anteriorly gently
angled (the apparently strongly angled anterior contour of the
frontal lobe of the lectotype is due to slight lateral distortion),
laterally subparallel-sided, the enclosing axial furrows diverging
anteriorly at approximately 15-20 degrees. Frontal lobe large,
moderately convex in lateral profile, extending slightly across the
line of the axial furrows, occupying an anteriorly marginal posi-
tion with regard to the front of the cephalon, bearing roughly five
rows of tubercles radiating anteriorly from a point midway between
the axial extremities of the anterior lateral glabellar furrows. Ante-
rior lateral lobes subtriangular in shape, very narrow adaxially
(exsag.) where they encroach backwards towards the axial ends
of the median lateral furrows. Median lateral lobes subrectangular
with posterior curvature to the back, narrow adaxially. Anterior
and median lateral lobes are fused abaxially. Preoccipital lobes
very narrow (exsag.) being merely a narrow ridge about one-
fourth as wide (exsag.) as the median lateral lobes, with appreci-
ably greater transverse convexity than the latter so that the abaxial
ends slope to a lower level.

A REAPPRAISAL OF THE TRILOBITE Scotiella j/

Anterior lateral glabellar furrows strong, wide, deep, slightly
sigmoidal, posteriorly oblique, almost reaching backwards to the
ends of the median lateral furrows. The latter are short, equally
deep and wide (exsag.), linear or gently curved, failing to reach
the axial furrows abaxially. Preoccipital furrows very wide
(exsag.), deep, slightly curved to anterior at abaxial ends, strongly
curved to the anterior at the adaxial ends, with a tendency to con-
verge towards the posterior extremities of the anterior lateral fur-
rows, there being a shallow tract along the proposed line of con-
fluence between on the one side the anterior and median lateral
lobes, which are very slightly raised above it, and on the other a
narrow (tr.) median longitudinal field raised to an equal level.

Occipital furrow curving slightly forward mesially. Occipital
ring considerably wider (sag. and exsag.) than the preoccipital
lobes, having a similar transverse convexity, rising above the level
of the glabellar side lobes.

Genae laterally extensive, without marginal furrow, without
an area of librigena anterior to the frontal lobe such as that pre-
sent in species of Acaste and Acastella. Postocular section of the
facial suture cutting the lateral cephalic margins opposite the
median lateral lobes; preocular section marginal immediately ante-
rior to and defining the limits of the frontal lobe. The preglabellar
furrow is represented merely by a slight marginal break in the
slope of the convexity of the frontal lobe. Adult genae are provided
with minute genal spinules; young holaspides have somewhat
longer, more delicate, spines. Eyes moderately large and extending
from the anterior lateral to the preoccipital glabellar furrows.

Nature of visual surface, hypostome and thorax unknown.

Pygidium subtriangular in outline, the lateral margins cul-
minating posteriorly in a caudal spine which is long in young
holaspides but considerably shorter in adults. Axis strongly convex
(tr.), raised throughout its length above the pleurae, terminating
abruptly before the posterior spine without trace of a post-axial
ridge. There are nine clearly defined rings and a trace of a tenth.
Rings 1-3, forming the anterior third of the axis, are clearly
defined, being separated by deep transverse furrows. The remain-
ing rings are separated by poorly-defined furrows. Ring 4 is entire,
similar to 1-3. Rings 5 and 6 are broadly V-shaped (sag.), the
apex pointing posteriorly, bearing, in well-preserved material, a

8 Postilla YALE PEABODY MUSEUM No; £12

small tubercle which appears to lie sagittally within the fifth and
sixth transverse furrows. Rings 7-10 are mesially interrupted by
a smooth band or groove running longitudinally along the axis
from the sixth transverse furrow. Whereas the halves of rings
7 and 8 are directed sagittally to the posterior, those of rings 9 and
10 point forwards. There are four well-defined pleurae, deeply
grooved and separated by extremely weak interpleural furrows;
a fifth is faintly indicated and there is sufficient space for a sixth
in the smooth area at the posterior end of the pleural field. Border
moderately wide, separated from the furrowed pleurae by a weak
marginal furrow. Lateral margins entire in adults.

Scotiella logani (Hall 1860)
pl. 2, figs. 1-8; pl. 3, figs. 1-8.

Dalmania logani. n. sp.; Hall, 1860, pp. 156-7, text-fig. 18
(untraced ).

Dalmanites logani Hall; Bassler, 1915, p. 385.

Dalmanitina logani (Hall); McLearn, 1918a, p. 32.

Dalmanitina logani (Hall); McLearn, 1918b, p. 130.
Dalmanitina logani (Hall); McLearn, 1924, pp. 167-8, pl. XX VII,
fig; 3: (GSC 6211), 4 (GSC 6210), 6 (YRM 481), nommigS
(GSC 5998).

Scotiella logani (Hall); Delo, 1935, pp. 406-7, text-figs. 12 (un-
traced) 3 Guntraced)s 145(GSE€ 621).

Scotiella logani (Hall, 1860); Delo, 1940, pp. 33-4, pl. 2, figs. 14
(untraced), 15 (untraced), 16 (YPM 481), 17 (YPM 25102).
Phacopina (Scotiella) logani (Hall); Struve, 1959, p. 0489, text-
fig. 386, 5 a-c.

Scotiella logani (Hall); Tomezykowa, 1962b, p. 192

TYPES. It has not been found possible to trace with certainty either
of the specimens used by Hall (1860, p. 156, text-fig. 18) to
illustrate Scotiella logani. All the specimens figured by McLearn
(1924, pl. XX VII) were labeled as plesiotypes and none of these
can be accurately matched with the original syntypes. I have,
therefore, selected from among McLearn’s plesiotypes, GSC 6210,
as neotype of the species.

DISTRIBUTION. All the available material is from the Arisaig coast
sections of Nova Scotia, the species occurring there in zones a-c

A REAPPRAISAL OF THE TRILOBITE Scotiella )

of the Stonehouse Formation and being most common in the last
(McLearn, 1924, p. 20).

AGE. As for Scotiella conservatrix cited above.

DIAGNOSIS. A species of Scotiella Delo 1935 with faint to very faint
anterior and median lateral glabellar furrows occasionally repre-
sented by fine upraised ridges; preoccipital furrows deep and wide
(exsag.); anterior and median lateral glabellar lobes fused abax-
ially; frontal lobe anteriorly depressed, gently angled, not encroach-
ing laterally across the courses of the axial furrows; genae with
minute posterolateral points; eye moderately large; seven lenses
at the maximum height (vert.) of the visual surface; pygidium
with eight to ten axial rings, mesially interrupted in the posterior
two-thirds of the axis; five pleural segments; border moderately
wide especially along the lateral margins, without distinct mar-
ginal furrow; margin entire in adults, denticulate in young hol-
aspides.

DESCRIPTION. The description is based on cranidia, glabellae and
pygidia. There is one specimen in which the eye is preserved. The
geometry of outline of the cephalon, the nature of the hypostome
and the thorax remain unknown.

Glabella trapezoidal, laterally subparallel-sided, anteriorly
gently angled. The axial furrows diverge at about 25-30 degrees
in small specimens, about 20 degrees in large adults. Anterior
lateral and median lateral glabellar side furrows faint to very faint
on internal moulds or represented by weak elevated ridges; very
faint to obsolete on casts taken from external moulds. The reliet
of the anterior part of the glabella is uniformly convex (tr. and
sag.). When visible the anterior lateral furrows are long, very
shallow, narrow (exsag.), and slightly sigmoidal, with a weak
posterior median deflection; as in Scotiella conservatrix (McLearn)
they tend to converge towards the adaxial ends of both the median
lateral and preoccipital furrows. The median lateral furrows are
rather wider (exsag.), shallow and considerably shorter, linear or
gently curved and failing abaxially to reach the axial furrows.
The preoccipital furrows are deep and wide (exsag.) in all speci-
mens regardless of preservation; they curve slightly to the ante-
rior at both their abaxial and adaxial ends, this curvature being
most strongly emphasized in small specimens. There is apparent

10 Postilla YALE PEABODY MUSEUM Nos ii

on some specimens a narrow (tr.) median longitudinal field,
slightly upraised, and separated from the equally raised anterior
and median lateral glabellar lobes by a faint, discontinuous furrow
lying along the proposed line of confluence between the anterior
lateral and preoccipital furrows.

Frontal lobe, when viewed in lateral profile, with lower con-
vexity than that of S. conservatrix, falling anteriorly to a very
narrow (sag.), dorsal intramarginal rim, running concentrically
to the anterior contour of the frontal lobe and representing the
preglabellar furrow; not extending laterally across the courses of
the axial furrows; bearing up to five rows of very faint tubercles,
radiating from a point between the adaxial extremities of the
anterior lateral furrows. Anterior lateral glabellar lobes subtrian-
gular, fused distally with the subrectangular median lateral lobes.
Preoccipital lobes very narrow (exsag.), about one-fourth the
width of the median lateral lobes but having a slightly greater
transverse convexity.

Occipital furrow deep, especially abaxially, wide (sag.).
Occipital ring raised above the general surface of the glabellar side
lobes, with a somewhat stronger transverse convexity than that of
the preoccipital lobes.

Genae postero-laterally provided with very small mucronate
points, similar to those of Acastella prima Tomezykowa 1962a.
Eyes moderately large, extending from the anterior lateral glabellar
furrows to the preoccipital furrows; sited a little closer to the
glabella than to the cephalic margins; rising to about the level of
the top of the glabella. The visual surface at hand is incomplete,
the posterior third being broken off, but the remainder contains at
least 73 lenses (giving an estimated total for the surface of approx-
imately 120) contained in at least 15 dorso-ventral files (an
estimated 22 for the complete surface) with rows of six lenses
alternating with seven at the maximum vertical height of the
surface.

Pygidium with subtriangular outline, laterally evenly rounded,
culminating in a short, sharp, inflected caudal point. There are
eight to ten axial rings and five pleural segments. The axis is
moderately convex (tr.), raised above the pleurae and abruptly
terminating before the posterior border without a marked post-
axial ridge. Rings 1-3 separated by deep and wide (sag.) trans-

EXPLANATION OF PLATES

PLATE 1

Scotiella conservatrix (McLearn 1924), Stonehouse Formation, Ari-
saig coast section, Arisaig, Nova Scotia.

Figs. 1, 2. YPM 472, holotype, exfoliated cephalon; fig. 1, dorsal view
showing minute genal spine, <4; fig. 2, lateral view, <4.

Figs. 3, 4. YPM 25111, exfoliated pygidium largely masked by matrix;
fig. 3, dorsal view, <4; fig. 4, axis showing mesially interrupted poste-
rior rings, x12.

Fig. 5. YPM 25113, early holaspid cranidium, exfoliated, dorsal view, X 4.

Figs. 6, 7. YPM 25112, exfoliated pygidium; fig. 6, dorsal view, <5;
fig. 7, lateral view, x5.

PLATE 2

Scotiella logani (Hall 1860), Stonehouse Formation, Arisaig coast
section, Arisaig, Nova Scotia.

Figs. 1, 2. YPM 481, plesiotype, internal mould cranidium; fig. 1, dorsal
view, 4; fig. 2, lateral view, <4.

Fig. 3. YPM 25106A, early holaspid, exfoliated cranidium, dorsal view,
«4.5.

Fig. 4. YPM 25104A, cranidium, latex cast from external mould, dorsal
view, <4; YPM 25104B, early holaspid pygidium, latex cast, oblique
view, <4.

Fig. 5. GSC 5999, plesiotype, plaster cast cranidium, dorsal view, «4.

Fig. 6. YPM 25114, internal mould glabella, lateral view frontal lobe, X 8.

Fig. 7. YPM 25109, exfoliated cranidium, dorsal view, <4.

Fig. 8. GSC 6210, neotype, plaster cast cranidium, dorsal view, <3.

PLATE 3

Scotiella logani (Hall 1860), Stonehouse Formation, Arisaig coast
section, Arisaig, Nova Scotia.

Fig. 1. YPM 25108, internal mould cranidium, dorsal view, <5.

Fig. 2. YPM 25106B, internal mould, visual surface, «10.

Fig. 3. YPM 25103, internal mould pygidium, dorsal view, <4.

Fig. 4. YPM 25105, internal mould pygidium, dorsal view, 4.

Fig. 5. YPM 25104B, early holaspid pygidium, latex cast from external

mould, showing entire axial rings and denticulate margin, 10.
Fig. 6. YPM 25107, pygidium, latex cast from external mould, dorsal
view, <4.
Fig. 7. YPM 25102, plesiotype, exfoliated pygidium, dorsal view, <5.
Fig. 8. YPM 25101, internal mould pygidium, dorsal view, «4.

A REAPPRAISAL OF THE TRILOBITE Scotiella et

verse furrows, rings 4-10 by weak furrows. Rings 7-10 appear to
be mesially interrupted as in S. conservatrix. Pleurae bear deep
and wide (exsag.) pleural furrows and are separated by very
weak interpleural furrows. Border moderately wide, smooth,
without marked marginal flattening, save posteriorly. Margin in
late holaspides apparently entire. One very small external mould
(YPM 25104b), approximate width 2.90 mm, approximate length
1.40 mm, associated with a cranidium of S. logani (YPM 25104a),
shows clearly eight uninterrupted axial rings and five pleural seg-
ments. The margin bears small denticulations which must also
have been present on the shell. During the ontogeny of the species
there appears to be a definite increase with size in the number of
posterior rings becoming mesially interrupted. Rings 5-10 may
have this characteristic in large specimens.

SUBFAMILY ZELISZKELLINAE Delo 1935
GENUS KLOUCEKIA Delo 1935
SUBGENUS KLOUCEKIA Delo 1935

Kloucekia (Kloucekia) obsoleta (Ulrich and Delo 1940)
new combination

Scotiella obsoleta Ulrich & Delo n. sp.; Ulrich and Delo 1940 in
Delo, 1940, pp. 34-5, pl. 2, figs. 21, 22 (USNM 79128, both
specimens).

TYPES. Cotypes (designated Delo, 1940, p. 34): USNM 79128,
73130:

OCCURRENCE. The species occurs in the Whiteoaks Sandstone of
Tennessee.

AGE. Lower Silurian, ? Llandoverian.

COMMENTS. The species obsoleta Ulrich & Delo 1940 is rejected
from Scotiella. Although photographs sent to me by Dr. C. Harper,
Jr., of the original syntypes show faint anterior and median lateral
glabellar furrows they also show a slight bifurcation at the adaxial
ends of the preoccipital furrows, where these are overdeepened.
In addition the pygidium of this species as described by Delo
(1940, pp. 34-5) is small, semicircular, non-spinose and has only
three well-defined pleural segments. All these characteristics dif-

12 Postilla YALE PEABODY MUSEUM Nop i

ferentiate it from other species of Scotiella described above, but
ally it with species of the zeliszkellinid subgenus Kloucekia
(Kloucekia) Delo 1935 to which it may be referred.

K. (K.) obsoleta is not the only representative of its genus
to have been confused with Scotiella. Kloucekia (Phacopidina)
major (Harper 1947) was originally placed in the same genus.
These assignations serve to underline the relationships between
zeliszkellinid trilobites of the Kloucekia type and the Acastinae.

The trend towards obsolescence of both the anterior and
median lateral glabellar furrows appears to be operative at more
than one time during the history of the Dalmanitidae and espe-
cially among those genera close to Acaste. The trend is observable
in Kloucekia, Calmonia and Phacopina as well as in Scotiella.
In each case there is considerable variation in the depth of furrow
impression. In Phacopina braziliensis (Clarke) (1890, pl. 1,
fig. 2) and P. devonica (Ulrich 1892) (see Kozlowski, 1923, pl.
4, figs. 7-11) these furrows are present, though faint. In P. anceps
(Clarke) (1890, pl. 1, fig. 3) and P. nylanderi (Clarke) (1907,
pl. 22, fig. 1) they are completely absent.

THE RELATIONSHIPS OF THE NORTH AMERICAN
SPECIES OF Scotiella

Some of the observations made by Hall (1860, pp. 156-7) in
his original definition of Scotiella logani differ from those given
above. Hall noted the presence of strong genal spines but these
cannot be confirmed in the material presently available. He further
noted (p. 157) six segments in the pleural field of the pygidium
and his text-figure shows seven, possibly eight, though on all the
material at hand only five are present.

The type-species, Scotiella logani, is in the majority of its
characteristics most closely related to S. conservatrix (McLearn),
differing mainly in the weakness of the anterior and median lateral
glabellar furrows and the lower convexities (exsag.) of the frontal
and lateral lobes. The tubercles prominent on the frontal lobe of
S. conservatrix, are also present but less distinct on that of
S. logani. The glabellar furrows in both species extend adaxially
to a similar distance but the rather distinctive, slightly upraised,
and narrow, median longitudinal ridge of S. conservatrix is very

A REAPPRAISAL OF THE TRILOBITE Scotiella 13

much less prominent in §S. logani. The pygidia are almost
inseparable.

In cephalic characteristics S. logani is very nearly homeo-
morphic with S. opatowiensis Tomczykowa 1962b, save that the
eyes of the latter are a little further distant from the posterior
border furrow and the frontal lobe is a little more anteriorly
rounded. The pygidium of S. opatowiensis is unknown but is pos-
sibly identical to that of S$. samsonowiczi Tomczykowa 1962b,
which occurs at the same localities and in the same beds.

Scotiella conservatrix is most closely related on cephalic
characteristics to S$. minor (M’Coy 1851). Both species have
strong glabellar furrows, but in the latter they are somewhat
shorter. In S$. minor the frontal lobe of the glabella is decidely
anteriorly angled (Shergold, 1967, pl. 2, fig. 1). The same com-
ments also apply to S. cf. minor with its distinctly pentagonal
glabella (ibid., pl. 1, fig. 9).

Scotiella samsonowiczi is in its cephalic form intermediate
between S. conservatrix and S. logani and also between S. con-
servatrix and S. minor. The glabellar furrows are present but weak
in the type specimens although other material from the same
locality shows considerable diversity in strength (Dr. Ewa Tom-
czykowa, pers. comm.). The genal spines are somewhat longer
than in other species of Scotiella at the equivalent morphogenetic
stage. The frontal lobe is anteriorly angled and the preocular sec-
tion of the facial suture is marginal as in S. minor. In the pygidium
there are six pleural segments as against five in S. logani and
S. conservatrix and the posterior axial rings are entire, as in young
holaspides of S. logani, not mesially interrupted.

The interruption of the posterior axial pygidial rings in adults
of S. logani and S. conservatrix is paralleled in other dalmanitid
genera only in Acastoides henni (R. Richter 1916), affecting
rings 5-8 in both A. henni posthuma R. & E. Richter 1952 and
A. henni henni (R. Richter 1916) (see R. & E. Richter, 1952,
pl. 2, figs. 8, 13). The reason for this development is unknown.

Young holaspides of Scotiella logani and/or S. conservatrix
appear to have pygidia with lateral marginal denticulations, these
appearing in Scotiella contemporaneously with similar structures
in young holaspides of species of Acastella. In the latter genus
these denticulations appear in the adult ontogenetic stages at a

14 Postilla YALE PEABODY MUSEUM No ite

later date, e.g. Acastella tiro R. & E. Richter 1954. They are also
present in young holaspides of species of Acastocephala Shergold
1966 but, as in Scotiella they do not persist into the adult mor-
phogenetic stages.

DISCUSSION

The type material for Scotiella originally described by Hall
(1860) has not been traced though it is possible that the two
specimens concerned (Hall, 1860, p. 158, text-fig. 18) were
unknowingly refigured by McLearn (1924). The specimens of this
latter author now constitute the type series. In this there are no
complete specimens with articulated cephala and pygidia; and
no such specimens have been observed in the recently collected
material. All the specimens available to date are isolated heads
or tails, these being preserved either as moulds or are exfoliated,
with the greater part of the shell usually missing.

Within the material at his disposal McLearn (1918a, 1924)
was able to differentiate two cephalic types, one referred to
Scotiella logani, sensu stricto, and the other to the variety con-
servatrix. The logani type of cephalon (McLearn, 1924, pl.
XXVII, figs. 3, 4, 6) is characterized by having a rather smooth
glabella with low sagittal convexity and faint, weakly impressed.
anterior and median lateral glabellar furrows. The axial furrows
of early holaspides diverge anteriorly at a greater angle than do
those of late holaspides (see pl. 2, figs. 1, 3, 5, 7, 8). The con-
servatrix type of cephalon (McLearn, 1924, pl. XXVII, fig. 1)
has a greater glabellar convexity (sag.) and there are three pairs
of clear, well-defined glabellar furrows, as in the genus Acastella.
Throughout morphogenesis the axial furrows appear to diverge
at an angle similar to that of the early holaspides of Scotiella
logani, sensu stricto, (see pl. 1, figs. 1, 5). The greater anterior
angle to the frontal lobe of the conservatrix cephalon figured by
McLearn (1924, pl. XXVII, fig. 1; YPM 472) is due to slight
lateral distortion. In this characteristic there is very little difference
between the two cephalic types on undistorted material.

McLearn (1924, p. 168) considered there to be every grada-
tion between the strongly furrowed cephalic form (conservatrix)
and the pauci-furrowed type (logani), this presumably influencing
his contention that the conservatrix type of cephalon should be

A REAPPRAISAL OF THE TRILOBITE Scotiella 15

regarded as having no higher taxonomic status than that of a
variety. His opinion was supported by Delo (1940, p. 34).

In originally assessing only the type material the present author
was inclined to disagree with the above stated view. Large holaspid
cephala appear to be quite distinct, though the number of charac-
teristics in cOmmon between the two cephalic types certainly
establishes their close relationship. Small holaspides, however,
show greater affinity and are often difficult to separate, the one
diagnostic difference being a slightly greater lobar convexity in the
conservatrix forms, which have as a result somewhat deeper fur-
tows. On examining additional material, recently collected and
kindly loaned by Professor A. J. Boucot, however, the differences
between specimens of large holaspid cephala gradually became
reduced. The statement, “in the distinctness of the anterior
two pairs of furrows ... the /ogani form ... grades more or less
indistinguishably into the variety conservatrix” (Delo, 1940, p. 34),
is justifiable, the conservatrix and logani cephalic forms being
interpreted as the end members of this morphological gradation.

McLearn made no differentiation between the two taxa he
recognised on pygidial characteristics. Delo (1940, p. 34), how-
ever, referred to S. logani a pygidium with a short, inflected, rather
incongruous, caudal mucronation (Delo, 1940, pl. 2, fig. 17; YPM
25102) and to conservatrix a non-mucronate pygidium (pl. 2,
fig. 20; YPM 25656). The latter has been re-examined by the
writer who concludes that it belongs not to Scotiella but to a
proetid trilobite.

It is indeed difficult to make a differentiation on pygidial
characteristics because all the pygidia represented in the collec-
tions examined, and referable to an acastinid genus, have the
Same segmentation, five pleural segments and nine to eleven axial
rings, depending on the morphogenetic stage attained. All the
pygidia observed are further characterized by a mesial interrup-
tion in the posterior rings of the axis. Nevertheless there are
pygidia similar to that figured by Delo (1940, pl. 2, fig. 17) as
S. logani. In addition there are others with lateral margins a little
more sharply drawn in, very slightly narrower borders and slightly
longer mucronations. These may belong to the conservatrix type
of cephalon. Just as the head of this species is closely similar to
that of Acastella, so is the narrower, more triangular pygidium.

16 Postilla YALE PEABODY MUSEUM Nos ii

It must be stressed, however, that the pygidia of logani and con-
servatrix are very similar and as such cannot be used confidently
as a basis for differentiation, a problem which may only be re-
solved by the discovery of a completely articulated specimen of
either species.

Thus among the type material of Scotiella there are two dis-
tinct cephalic types, which may be end members of a gradational
morphological series, accompanied by scarcely distinguishable
pygidia. There can be no question of the observed differences being
attributed to preservation or to morphogenesis, for specimens,
quite distinct and of comparable size, occur together at the same
localities in both calcareous and argillaceous matrices. That sexual
dimorphism may account for these differences might be considered
but cannot be proved. It is interesting to note in this respect that
Tomezykowa (1962b) has recently described two species of
Scotiella from the Holy Cross Mountains, southern Poland:
S. samsonowiczi, having glabellar furrows present but incised to
varying depths, and S. opatowiensis, having weak anterior and
median lateral furrows. Only one type of pygidium is known and
this is articulated with the samsonowiczi type of cephalon. Both
species occur on a similar horizon in the Rzepin Beds (Pod-
lasian = ? Downtonian) at Lezyce-Belez near Opatow and at
Lipniczek near Sandomierz (Tomezykowa, 1962b, p. 203).

The inclusion of both strongly and weakly furrowed cephaia
within the single genus raises certain taxonomic points. Delo
(1935, p. 409) in erecting Scotiella originally confined the genus
to the type species, S. logani (Hall), the generic diagnosis thus
incorporating the observation “anterior glabellar furrows faint to
obsolescent.” This diagnosis was left largely unmodified in a later
paper (Delo, 1940) though in considering the pygidium the earlier
definition “rounded, with short spine” was altered to “rounded,
with or without short spine” (p. 33), presumably to reconcile the
differing species which Delo attributed to the genus at this time.
The variety conservatrix was included in Scotiella in his paper, in
spite of the original definition which excluded trilobites with
strongly defined glabellar furrows. No emendation was made to
the diagnosis to account for this inclusion.

Disregarding the latter assignation later authors have come to
regard the faintness of the anterior glabellar furrows as absolutely

A REAPPRAISAL OF THE TRILOBITE Scotiella ilyé

diagnostic of Scotiella. Struve (in Moore, 1959, p. 0489) for
example has considered Scotiella as representing a subgenus of
Phacopina Clarke 1913, in which the anterior and median lateral
furrows may be similarly faint. His diagnosis retains Delo’s (1940)
statements concerning the nature of the pygidium of Scotiella. If
these authors are to be followed strictly, then only such species as
S. logani with the anterior two pairs of furrows faintly defined,
can be classed within the genus.

With respect to the differences and similarities between the
cephalic forms noted above, this situation is somewhat unsatis-
factory. Until it can be conclusively proven that the /ogani and
conservatrix forms are conspecific or otherwise, I would prefer
to regard them as separate species, thus following the procedure
adopted by Tomezykowa (1962b) in dealing with the Polish
species. The generic diagnosis of Scotiella has been emended here
to embrace both strongly and weakly furrowed glabellar forms.
Some allowance has also been made for the differing pygidial
characteristics between North American and European species.
The species thus included in the genus are: Scotiella logani (Hall
1860), S. conservatrix (McLearn 1924), S. samsonowiczi Tom-
czykowa 1962b, S. opatowiensis Tomczykowa 1962b and S. minor
(M’Coy 1851).

CONCLUSIONS

1. The exact taxonomic status of Scotiella must remain in
doubt until fully articulated specimens of either S. logani or
S. conservatrix are discovered, in which event the correct assign-
ment of the pygidium may be facilitated.

2. McLearn (1924) and Delo (1940), impressed by the
apparent morphological transition between the logani and con-
servatrix cephalic types and being unable to distinguish associated
pygidia readily, referred both species to Scotiella, a procedure
followed here.

3. It is suggested that the poorly furrowed cephalon represents
a derivation from the strongly furrowed type, though there is a pos-
sibility that this difference is the result of sexual dimorphism.

4. The strongly furrowed Scotiella of the Stonehouse Forma-
tion probably represents a rapidly evolved branch of Acastinae

18 Postilla YALE PEABODY MUSEUM No: tt

derived from a parent species of Acaste at a time when Acastella
was evolving from a similar source in northwest Europe.

5. Acastella, present in Europe and north Africa from Lud-
lovian to Siegenian time, has not been reported from North
America. Scotiella, present from Ludlovian to Lower Gedinnian
time in North America, is only sparsely represented in Europe,
where iis range is confined to beds about the Siluro-Devonian
passage (late Ludlovian to early Downtonian). Scotiella may
thus be interpreted as the temporal equivalent in North America
of the genus Acastella in Europe and north Africa.

ACKNOWLEDGEMENTS

For allowing me access to either their personal collections
or to Museum material in their care I am gratefully indebted to
Dr. C. MacClintock, Peabody Museum of Natural History, Yale
University, New Haven; Professor A. J. Boucot, California Institute
of Technology, Pasadena, California; and Dr. T. E. Bolton, Geo-
logical Survey of Canada, Ottawa. I am especially grateful to
Dr. Ewa Tomcezykowa, Instytut Geologiczny, Warsaw, for much
helpful discussion and for her hospitality during my brief visit to
Poland. Dr. C. Harper, Jr., U. S. National Museum, Washington,
kindly sent me photographs of the types of Scotiella obsoleta and
Dr. G. K. B. Alberti, Geologische Staatsinstitut, Hamburg, Ger-
many, passed on to me material from Professor Boucot’s collec-
tions. I thank Professor T. S. Westoll, University of Newcastle
upon Tyne, Newcastle upon Tyne, England, for providing me
with facilities to complete the study, and Dr. A. A. Opik, Bureau
oi Mineral Resources, Canberra, Australia, for his critical reading
o. the manuscript. The research was partially financed with the
aid of a travel grant from the Natural Environment Research
Council.

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A REAPPRAISAL OF THE TRILOBITE Scotiella 19

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—_———. 1924. Palaeontology of the Silurian rocks of Arisaig, Nova

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