characteristic being in its central part elongated in a short evenly
rounded projection. The side wings are triangular acuminate, bent a
little backwards and towards the interior surface. There is only a
single rounded field passing into an evenly bent border, in front of
which the projecting, elliptic maculæ lie. A second pair of wings
stretches backwards near the posterior margin. We have not obtained any
sections of the maculæ.
The cephalic eyes figs. 36-38 are covered with an uncommonly thick
stratum of homogenous shell, one and a half times as thick as the
subjacent lenses. These are comparatively broad, above passing
indistinctly in the covering stratum, below, at their basis, convex.
In a horizontal section figs. 33, 34 they exhibit the common hexaedral
or pentaedric aspect, their exterior sides being white and confluent
without any separating lines. Their interior is dark and from the
polygonal sides white lines go in giving the whole the appearance as
of a starry, composite coral with its septa. The correspondence in
structure with Bronteus laticauda pl. II fig. 7 is striking. A narrow
space separates the surface of the eye from a nearly similar patch
below the eve on the cheek 35 _b_, 38 _b_. But there the position
of the composing strata is singularly reversed and the spongious or
pseudo-prismatic stratum lies close to the outside and the homogenous
stratum on the inside. The white longitudinal lines are well marked
out and regular in the vertical section, fig. 38 _b_, indicating the
prismatic structure most clearly.
=B. barriensis= MURCH.
Pl. II figs. 31, 32.
The hypostoma fig. 31 is of so transverse a shape that the breadth much
surpasses the height, the former being 6 millim., while the latter
attains only 3,5 millim. The anterior margin is so much arcuated and
sloping backwards that it forms an obtuse angle. The side wings are
triangular and acuminated and from them a thick pad runs backwards and
forms the posterior margin. Below the largest field of the exterior
surface the maculæ rest on a ridge having a much elongated, vermiform
shape and sunk in the surface (fig. 32) a little more than three times
longer than broad. In its shape it approaches much to the hypostoma of
Bum. insignis HALL as delineated by SALTER pl. 27 fig. 7.
In another, undetermined Bumastus (pl. II figs. 47, 48)[40] the
hypostoma (from Klints, Othem, isle of Gotland) is of a more elongate
obovate form, the anterior margin elevated, rounded, the terrace lines
faint, the tubercles are larger than in the former Bumasti, oblong,
curved, beanshaped, evenly rounded and smooth.
[Footnote 40: Probably the same as Bum. sulcatus pl. XII fig. 12 in my
paper on the Trilobites of Gotland 1885.]
Another of the new species is one that LILJEVALL has found at Korpklint
near Wisby (Pl. II figs. 41-46). The hypostoma is more elongate than
transverse with the anterior margin regularly arcuated, by far not
so prominent as in B. sulcatus and the former. By a shallow groove
the exterior surface is divided in two fields, the anterior one the
largest and covered with a few, distantiated, concentric terrace
lines. The posterior field is smooth, nearly even and the maculæ lie
just in the groove, with their axis oblique to the longitudinal axis
of the hypostoma, beanshaped and smooth. The cephalic eyes show in
a horizontal section hexaedral white walls enclosing a dark space
in which some indistinct radii emanate, fig. 41 _a_. In the vertical
sections the prisms are narrow and elongate and the integument by far
not so thick as in Bumastus sulcatus, fig. 42, 43. The border zone
of the eye in this (fig. 41) as well as in B. sulcatus, as seen in
horizontal sections, agrees with that of the Asaphidæ.
=Bumastus= sp. inlet.
Pl. III fig. 1, 2.
In a detached piece of limestone, found in Gotland, at Norderstrand,
near Wisby, two hypostomas and a free cheek lay embedded along with
a coral of the genus Acantholithus and a Bronteus probably belonging
to a new species. As the coral has not been found above the uppermost
beds of the Lower Silurian it is probable that the trilobites also are
derived from the same horizon.
The hypostoma, figured pl. III fig. 1, is broadly tongueshaped, with a
short, blunt, triangular wing on each side of the anterior margin. The
exterior side is nearly completely occupied by a single large field,
which is convex and decorated by sparse terrace lines. Below this a
smooth, nearly even plane, reaching to the inferior, elevated border
of the hypostoma. The two tubercular macula' are situated exactly on
the boundary line between the convex and the plane field. They are
elongately ovate, pointed outwards, rounded inwards, with smooth and
glossy surface. That portion, on which in the species of Bronteus
the granular spot rests, is transversally wrinkled by some faintly
elevated, sigmoid lines (fig. 2). It would have been of great interest
to investigate the interior structure of these curious maculæ, but the
scarcity of the material has prevented our doing so.
The other hypostoma, pl. III fig. 3-5, is larger and has the terrace
lines more distantiated and forming more open curves, but for the rest
it is of the same shape as the smaller, so that we may not ascribe
these small deviations to a specific difference. The maculæ are more
elongated, narrow, curved tubercles, thus differing from the next
preceding. A section running through its left tubercle does not show
any structure, but the shell of the maculæ is extremely thin, thus
contrasting strongly with the surrounding thicker shell, fig. 4 _a_.
The cephalic eye, again, remaining on the free cheek found in the same
piece of limestone and probably belonging to the same specimen, has its
surface well preserved and exhibits semiglobular lenses in low relief,
fig. 5.
=Calymmene= BRONGN.
In the following species of this genus hypostomic tubercles have
formerly been recorded.
_Cal. Blumenbachi_ SALTER Monogr. pl. 8, fig. 9. The identity of the
species is dubious.
_Cal. duplicata_ SALTER Mon. pl. 9, fig. 22. The tubercles rather more
linear and approximated than in the subsequent. SALTER calls them »two
small transverse lobes ... forming a nearly continuous ridge».
_Cal. tuberculata_ ANGEL. Tab. XIX fig. 5 c from the inside.
It is remarkable that the eyes or that part of them where the cornea
and the lenses should be found, has been destroyed and entirely lost in
all specimens of the Calymmene known to us, many hundreds having been
searched and every one with a lacuna on that spot. It must have been
of an excessive thinness. We know only of one instance, the Bohemian
Calym. Arago, in which BARRANDE has seen the eye intact and provided
with a small number of about eleven sphærical lenses.
=Calymmene intermedia= LDM.
Pl. III figs. 6, 7.
The clypeiform hypostoma is divided in two fields, one anterior larger,
in the centre elevated in a short, blunt knob, and a posterior, bearing
the two elevated rounded maculæ, just below the semicircular groove
which separates it from the anterior field. These fields are surrounded
by a large border which is posteriorly emarginated through a short
rounded sinus. The surface is entirely covered by small semiglobular
wartlets perforated by a straight pore or duct, which being filled
with a black mineral, probably iron pyrites, gives a peculiar and
characteristic aspect to the sections. In the same manner the whole
mass of the hypostoma is pierced by straight, black lines, also filled
up pores, starting from the outside and ending before attaining the
inner surface.
The maculæ are prominent, separated from the hypostoma through narrow,
distinct grooves, ovate, with the pointed end directed obliquely
outwards, against the margins of the hypostoma. They are covered with
wartlets and leaving only a little oblong spot free, quite smooth, this
being consequently the macula proper. But in a longitudinal section
there is not the least distinction between this macula and the other
hypostoma, only, that it is free of pores.
=Calymmene tuberculata= BRÜNNICH.
Pl. III figs. 8, 9.
We have succeeded to prepare a horizontal section of the macula. This
is oval, perfectly homogenous and without any structure proper, showing
only indistinctly a mottled medley of pale, brownish spots in the clear
mass. There is in both maculæ a small dark, angular spot placed in
their inferior part, fig. 9.
=Centropleura= ANGELIN.
This author has delineated most distinct maculæ in Centr. Steenstrupi
pl. III fig. 4, b. two, small elongate darkish spots, near the
posterior margin. I have not seen any specimen of this trilobite and
have consequently not been able to follow up ANGELIN'S observation.
=Chasmops= M'COY.
Pl. III fig. 10.
In his work on the Russian Phacopidæ FRIEDR. SCHMIDT has given the
figures of Chasmops Eichwaldi and Ch. Wesenbergensis showing, as it
were, patches of black maculæ. But as there is no mention of them, and
as they are quite unlike the macula? which are described here, I am in
doubt of their real nature. We have figured a macula from the hypostoma
of a Chasmops, probably Ch. macroura, from a drift block near Rostock.
It is elongate and narrow, more than four times longer than broad. Its
smooth surface is a little scooped out and no structure is observable.
=Chirurus= BEYRICH.
We find the hypostomic maculæ annotated and delineated as occurring in
the following species.
_Ch. bimucronatus_ SALTER pl. 5, fig. 5 as two narrow elongated pits,
surface seems intact. No mention of them in the letter-press.
_Ch. exsul_ SCHMIDT pl. VI fig. 9. Indications of the oblong, narrow
maculæ.
_Ch. macrophthalmus_ SCHM. pl. VII, figs. 1 c, 2. Faint indications of
narrow pits.
_Ch. Quenstedti_ BARR. Tab. 42 fig. 3. Maculæ near lower border as two
narrow slits.
_Ch. spinulosus_ SCHM. pl. VII fig. 10. The lateral pits well visible.
_Ch. tumidus_ SCHM. pl. VIII, fig. 22. The pits are short, but present.
The exterior surface of the hypostoma is entirely covered with small
wartlets, closely set, of different size in the various species,
and spread between them lie a great number of elongate smooth spots
dispersed, on the interior side of the hypostoma showing an excavated
surface (pl. III fig. 16).
=Chirurus (Cyrtometopus) clavifrons= DALM.
Pl. III figs. 17-21.
The shape of the hypostoma is shown in fig. 21 pl. III. It is regularly
shield-formed with posterior margin rounded. A shallow groove running
parallel with the margins forms a large, faintly elevated border. The
anterior margin projects on both sides in a short, backwards directed,
broad and flat wing, hollowed out with a pit on the front side, and
there is a posterior lateral wing, midways between the anterior and
posterior margin short, blunt, directed obliquely backwards. The whole
exterior surface is covered with diminutive tubercles, the above
mentioned smooth spots interspersed on the central disk. A little below
the middle there are two lengthened pits, so shallow that they often
are not discernible. In a specimen of Chirurus spinulosus NIECZKOWSKI
from Estland there are two, almost 3 mm. long dots, one on each side
above the maculæ as the fig. 21 shows and in several others of this
generic group there are also indications of similar. I cannot compare
these dots with anything more than the lengthened spots visible in
Acidaspis crenata.
The maculæ are wanting in this species, but the cephalic eyes are well
developed. A section of them fig. 19 shows the enormous difference of
the shell in the eye and the surroundings where the shell surpasses it
many times in thickness. The eye consists in fact only of the ovate,
beadlike lenses of which a string is seen sectioned in the figure
mentioned. More enlarged (fig. 20) a nucleus is visible in each lens,
and in a horizontal section (fig. 18) a little below the surface, where
they are more pressed against themselves, they have a polygonal shape.
The figure 17 seems to represent lenses that have been much changed
interiorly, having only a narrow zone left of the primary structure.
=Chirurus glaber= ANGELIN.
Pl. III fig. 11.
As a sample of the shape of the surface of the eyes in this genus, we
have given a figure, showing the small rounded lenses.
=Chirurus ornatus= DALMAN.
Pl. III figs. 12-14.
The cephalic eyes have globular lenses, of more than double the size of
those in Chir. clavifrons. The difference between the lenses and the
surrounding shell amounts at the highest to thrice the former, while
in Ch. clavifrons it is at least seven times as much. In a horizontal
section the lenses have a little, darkish irregular nucleus surrounded
by a radiated structure (fig. 12).
The maculæ (fig. 14) are slightly concave, oblong, smooth, surrounded
by comparatively large granulations.
=Chirurus speciosus= DALM.
Pl. IV fig. 1.
The exterior surface of the hypostoma is sparingly covered by granules
of larger size than in other Chiruri. The maculæ as seen in a cast
are prominent near the posterior border, sunk in their centre and
surrounded by a narrow distinct border line. In a horizontal section
it as not been possible to detect any peculiar structure, only a dark
border surrounding the interior clear surface.
_Chirurus spinulosus_ NIECZKOWSKI.
Pl. III fig. 15.
We have had the interior surface of a hypostoma at our disposal from
the lower Siluria, of Esthonia (Kuckers C^2) belonging to Dr. G. HOLM.
The macula are well preserved, standing out black on the white surface,
oblong, 1,5 millim. in greatest length (fig. 15). There are indications
as of a great number of small lenses on these maculæ. Remarkable are
the two elongated spots, almost 3 mm. in length, above these maculæ, of
which already mention has been made under Ch. clavifrons.
=Chirurus= sp. indet.
Pl. III fig. 16.
The hypostoma of an undescribed species from Öland. The maculæ are
lengthened, ellipsoid and smooth tubercles lying in a groove. The
finely granulated surface of the hypostoma shows rare smooth spots
interspersed, being on the inside smooth pits, from which again in
casts of the hypostoma larger tubercles are moulded. Of the same nature
are those that are visible on the nucleus of Chir. speciosus and
others. There are still some undescribed Lower Silurian species, for
instance one nearly related to Ch. conformis with tubercular maculæ. A
large hypostoma from the Leptæna limestone of Dalecarlia, 33 millim. in
length, has a longitudinal macula, 2 millim. in length, as seen on the
inside of the fragment.
On pl. VI fig. 10 a little hypostoma is delineated that shows some
resemblance with that of the Chirurus, but probably belongs to some
other, unknown genus. It is Upper Silurian, found at Mulde in Fröjel,
Gotland. It is of an elongated ovate shape, with the anterior border
faintly arched, the anterior wings broad, truncate. A narrow elevated
border surrounds the lateral and posterior margins. The somewhat
vaulted surface is covered by fine granulations, and the macula,
situated on equal distance from the anterior and posterior margins are
ovate, smooth and directed obliquely inwards. There are two minute
pointed processes on each side of the lateral borders and one on each
side of the pointed posterior margin.
=Ctenopyge= LINSN.
=Ct. spectabilis= BR. (I, pl. XII, fig. 12 a).
A small lengthened, apparently smooth hypostoma with two globular
tubercular maculæ near the posterior border. No mention made of them
in the description of BRÖGGER. Cambrian. I am not, however, quite sure
whether this really belongs to a Ctenopyge, as it rather more resembles
the type of a Peltura as shown in Pelt. scarabæoides. As Ctenopyge is
so nearly related to Sphærophthalmus it could be expected to see its
hypostoma of the same type and the maculæ entirely wanting. The eyes of
this genus have been described above at page 29.
=Cybele= LOVÉN.
=Cyb. bellatula= DALMAN.
Pl. IV fig. 2.
We give a new figure of the hypostoma to complete that of FR. SCHMIDT,
pl. XIII fig. 9. The anterior wings are larger and obtuse, excavated
below and the border rim is not so distinct all round as he has
figured. There are two pair of oblique, lengthened grooves above each
other. The opposite do not, however, join to form a coherent groove
across the median field of the hypostoma, which is level between them.
No maculæ. Nearer the anterior border close below the wings, there is a
small roundish, dark spot. The surface of the hypostoma is granulated.
=Cyphaspis= ANG.
=Cyph. elegantula= ANG.
Pl. III figs. 22-25.
The hypostoma is elongated, anterior margin evenly arched, anterior
wings triangular, lateral margins faintly curved as well as the
posterior margin, at both sides of which there is one diminutive
spine. The posterior wings are short forming a spiny process from the
lateral margin. The surface of the hypostoma is smooth with a shallow
transverse groove on the inferior moiety and two corresponding lateral
impressions below it, one on each side. The elevated lateral borders
are longitudinally striated by a few terrace lines. There are no maculæ
visible. The eyes consist f short hexagonal prisms (figs. 22, 23)
nearly resembling those of Proetus.
=Dalmanites= EMMRICH.
In this large genus the hypostoma has been figured in a great number
of species. But it is only in the following that we, at least in the
figures, if not in the descriptions, are able to detect the maculæ.
_D. atavus_ BARR. Suppl. pl. 5 fig. 14.
_D. Calypso_ J. HALL, vol. VII, pl. XI A. fig. 21 p. 66
»Postero-lateral pits, moderately strong and elongate». There are casts
of the two well distinct maculæ.
_D. caudatus_ BRÜNN.
a. FORBES and SALTER in British Organic remains, Dec. II pl. 1, fig.
3 give a good figure, showing the oblique pitlike maculæ. On page 2
is told that »a pair of lateral strong indentations indicate a second
furrow above» (»the transverse furrow between the tip»).
b. SALTER, pl. 3, figs. 7, 8, bad figures, the description verbally the
same as above. What ANGELIN pl. VIII, fig. 2 c gives as the hypostoma
of »Ph. caudata» is in fact the hypostoma of a species of Lichas.
_D. Mac Coyi_ BARR. Supl., pl. 13 f. 32. This magnificent hypostoma
belongs to the same group as D. micrurus HALL as to which we may
hesitate whether there not be a double pair of maculæ above each other
near the posterior border. In this species, however, there is the
transverse lower groove and above probably the two maculæ united by a
groove so closely as to resemble the lower groove.
_D. micrurus_ J. HALL, Pal. N. Y. III pl. 74 fig. 20. Shows, as it
were, a double pair of maculæ, very like D. spinifer BARR.
_D. rugosus_ BARR. pl. 24 f. 23. The two maculæ in the ordinary place,
without being united by a groove.
_D. socialis_ BARR. pl. 26 f. 21. Rather of an uncommon shape, not so
triangular as in the other species, the two maculæ distinct as narrow
slits. P. 553 »Vers l'extrémité du corps central, on aperçoit de chaque
côté, près du bord, une impression oblique, alongée et arquée».
_D. spinifer_ BARR. Pl. 25, fig. 20. A large beautifully preserved
hypostoma, shows what I think we positively must interpret as a double
pair of maculæ close above each other. As stated above there is
reason to believe that in other species of Dalmanites there also are
indications of four maculæ, though not so evident as in this species.
BARRANDE says nothing about this remarkable feature.
=Dalmanites imbricatulus= ANGELIN.
Pl. III figs. 43, 44.
The interesting image, as given by the agglomerated eyes, is
represented in the magnified figure 43 Plate III. The lenses lie there
separated from each other at much varying distance, some in close
contact. The presence of the delicate covering membrane is clearly
seen, being of white colour contrasting with the black, glossy lens.
It is much lacerated and only preserved around the periphery. The size
of the ocelli is on an average 0,5 mm., a little one has 0,3 mm. The
surface between the ocelli is most finely granulated. The granules
scarcely attaining the fourth of the granules in Dalm. vulgaris.
In a vertical section the regular biconvex lenses are seen to be
covered with the extremely thin integument, which is a direct
continuation from the test. The test between the lenses is perforated
by some longitudinal tubes, as usual in the skeleton of the trilobites.
We have not found any hypostoma with the maculæ.
=Dalmanites obtusus= LDM.
Pl. III figs. 45, 46.
We have not succeeded in finding any hypostoma, but as the structure
of the cephalic eyes is sufficiently well preserved, we here describe
it. The lenses seen from the surface look globular, and in a vertical
section they are ovate and in a horizontal circular. They are
covered by a very thin and delicate membrane, that envelops their
superior moiety completely and between the eyes it is enclosed by the
surrounding test and growing out from it. In the horizontal section,
fig. 45, it looks as a circular frame around the lenses and the
membranes of two contiguous lenses sometimes lie so close, that they
entirely fill up the interspace between the lenses, leaving only a
narrow slit between them marking their boundaries. The space between
the lenses, fig. 46, is porous, being perforated by tubes, which
continue vertically down through the shell of the cheek.
_Dalm. sclerops_ DALMAN.
Pl. IV fig. 3.
Commonly this species has been ranged with Phacops, but it is evident
that it as to the conformation of its glabella and the head in general
is highly discrepant, and in these respects is more concordant with
Dalmanites, though still deviating as for instance in the pygidium and
some details of the head. Therefore it may be justified with FRIEDR.
SCHMIDT[41] to consider it as a generic division, though not, as he has
it, as an independent genus, but as a subgenus of Dalmanites.
[Footnote 41: Revision, I, p. 76.]
The granulated hypostoma differs from that of Dalmanites proper in
having the anterior margin strongly arched, the pointed wings almost
on the median line of the hypostoma. There is one groove near the
posterior border and the maculæ lie as two, narrow long, crescentic
grooves close below the wings. The few sections give no clear idea of
any structure.
The cephalic eyes are constructed on the same plan as in the previous
species, the lenses being surrounded by a frame.
_Dalm. vulgaris_ SALTER.
Pl. III figs. 47-52.
The hypostoma has the common shield-like shape, fig. 51, anteriorly
slightly arcuated, the short obtuse wings curvated towards the interior
surface. It is finely granulated. The groove does not go so near the
cuspidate posterior margin as in other species. The two maculæ, fig.
52, are narrow and elliptic, somewhat convex and lie in a little
concavity, a narrow smooth space around is devoid of the granules,
which cover the surface of the rest. They show absolutely no structure,
excepting a few indistinct blackish spots.
The cephalic eyes have been often described and delineated. Most
detailed are the descriptions and figures given by SALTER in the
Memoirs of the Geological Survey Dec. II. pl. 1. In the figure 4 a
part of the surface is shown in well preserved state. He says that
»the cornea is ... present and distinctly convex over each lens, the
intermediate portions being ornamented with tubercles and granules».
He thinks also that there are undeveloped or small lenses between the
larger. His fig. 5 represents the frames around the lenses, these being
probably lost. His explanation of fig. 6 I cannot understand. There are
weathered or spoilt lenses figured.