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Reprintcl from The Ottawa Xati-ralist, V.>1. XXIV, X.^v . I'Mo. with-
out change' in jja^in^;. PuMishf'i X'>v ^, I'Mii.]

|0

ON TWO NEW TRILOBITES FROM THE
CHAZY NEAR OTTAWA

By PERCY E RAYMOND

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THE OTTAWA NATURALIST.

VOL. XXIV, PLATE II.

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OM TWO NEW TRILOBITES FROM THE CHAZY NEAR

OTTAWA.*

By Percy E. Raymond.

Bathyurus superbus Sp. Nov. Plate II. Figs. 1—3.

Entire test broadlv oval in outline, the breadth var>Hng
from 6 o 8 of the length. Dorsal furrows deep on tliorax and
PvS^dium but shallow on the cephalon. Axial lobe narrow and
?atler^ow. not being raised much above the general level of the

'"^"ceDhalon short and wide, surrounded by a very narrow
concave border Glabella nearlv smooth, expandmg slightly in
front of the eyes marked by two pairs of faint furrows^ Eyes
?0 ifrge low extending bJck to the neck furrow and forward
to^he middle of the glabella. Free cheeks wide convex the
trenal angles drawn out into spines which extend back to the
fifth or sfxtb se^ent of the thorax. Surface of the test smooth
except fi^firieTrL which are rather prominent on the inner

'''%i:^:^ll7nt:e%n.s. Axiallobe narrow. Pleura with

'^""^PvSdhL nearly semicircular in outline, with ^ broad con-
cave bofdtrTndlVw. smooth axial lobe. Jhe pleura^ lobes are

S:cS\^sI°Se^a^^^^er&3{£^

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"'"^The hvTo.-.^a is about as broad as long, almost straight

stoma of Baihvurus extans, but broader in t'ont.

T enjrth of the largest specimen 74 mm., width 58 mm. A
smaller s^eci^en is 4lmm.'long and 25 mm. wide. One pygt-

Tpublished by permission of the Director of the Geologicl Survey of Canad..

l.iU

TlIK (JTTAWA N'ATURALIbT.

[Nov.

(iiuni IS IX mm. hm^ and iO mm. uulc, while another is 12 mm.
lon^ and 21 nmi. \vi<U A \ery large cephalon is 27 mm. long
and 58 nmi. wide.

This S]iecies is (.losely related to Buthyiinis Citaii.s (Hall),
l)Ut ditkrs irom that species in being wider, in having a much
less con\ e.\ axial lobe, a depressed and rounded, instead of a very
convex and subtnangular ])y^'idium, an'i a much wiiier concave
border on the pvgi<lium. The surface of tlie glabella of B. cxtiim
is ()uite granulose, while the test in this s[»ecies is smooth. The
species also altams a much larger size than li. cxtiiiis or any other
species of the genus.

Locality. Tliis s])ecies seems to oe rather common in a
laver of dark gray dolomitic limestone southwest of the outcrop
of the Black River an(] Lowville at La Petite CHaudicre,
Mechanicsville, Ontario, and has not yet l)een observed in any
other siralum. This layer is sui)posed to behjng to the Chazy.

The entire specimen, which is probably the largest Bathyurus
known, was colkxted by Mr. J. E. Xarraway, and is in his col-
lection. The other si)eciniens figured were collected L-y the
writer and are in tlie collection of the (leological Survey. Mr.
N'arrawav has a pygidium of this sjiecics which he collected some
vears ago from a loose fragment of rock in Ottawa South.

The onlv other Bathyurus known from the Chazy is B.
auj^dini Billings, a species which is peculiar in that the axial
lol)e of the pygidium extends across the border to the posterior
margin.

ISOTELUS AREN'ICOLA SP. NoV.

For a number of years fragments of a large Isotelus have
been found in the sandstone of the Chazy about Ottawa, but
as the cephalon was unknown, it was not possible to determine
what species was represented. It has usually been listed as
Asaphus or Isotelus canalis. (See Sowter, T. W. E.. Ottawa
Naturalist, Vol. IL. pp. 11-15, 1888; Ami. H. M., Appendix to
Dr. Ells' "Geology of Ottawa and Vicinity." 1901). A free
cheek recently found by the writer at Britannia supplies the
missing information, and this, with the large headless specimen
collected by Richardson at Deschenes, furnishes the material for
the description which follows.

DESCRIPTION. — Cephalon, judging from the free cheek,
nearlv three-fourths as long as broad, surrounded bv a wide
concave border. Eves large, situated less than their own length
from the posterior margin of the cephalon. Free cheek broad,
with the genal angle drawn out into a short, broad, flat spine.
Thorax of eight segments, the axial lc:)be narrow for the genus—
one-third the total width. Pygidium roughly triangular in out-

1910]

The Ottawa Naturalist.

131

Fig. 1. Inntflua arrnirola Out-
line of free check and portion of cran-
idium from Britannia One-third
natural size

Kir 2. iHotrlux afCHietUa. Outline of the
specimen collected by kictianlson at Ueichenes.
One-lhinl nafiinil 3iz< .

line, three-fourths as long as wide; border concave. On the
specimen described, which is a cast of the interior, there are two
rather distinct ribs on each of the pleural lobes. The axial lobe
is hardly distinguishable.

Width of thorax at back of fourth segment, 1.35 mm., width
of axial lobe at same point, 45 mm. , length of pygidiimi, 98 mm.,
width, 130 mm. The specimen is only very slightly flattened.
The total length of this specimen appears to have been about ten
inches. Another specimen, described below, seems to have been
at least four inches longer.

This species is more closely allied to Isotclui, ^igas than to
any other species, the pygidia of the two forms being almost
alike. The axial lobe of the thorax of the species here described
is, however, much narrower than in either /. gigas or /. maximus.
I. gigas has no genal spines at maturity, and / maximus has a
shorter and more nearly semicircular pygidium. /. harrisi has
a wider and shorter cephalon, and /. plalymarginattis has a much
wider concaxe border around the pygidium

A rather remarkable specimen of tiiis same species was
found by W. C. King, Esq., on the shore of Lake Deschenes at
Britannia. This specimen is an impression of the lower surface
of the trilobite, and shows a longitudinal ridge corresponding to
the central furrow along the axis of the ventral side of the animal,
10 pairs of transverse furrows, and the impression of the hypo-
stoma — first noticed by my friend. Mr. Narraway. The doublure
of the pygidium has also left a wide smooth impression, but in
the cephalic region the hypostoma is the only portion of which
there are any traces remaining. The specimen was fovmd bv Mr

1.^2

The Ottawa Naturalist.

(Nov.

King on a watervvorn surface of the beach, partially covered by
the shingle, and many details of the structure have doubtless
been removed since it was first exposed to the action of the
elements. The outline of the hypostoma is rather faint on the
specimen, but the excellent photograph made by Miss Bentley
brings it out clearly. The forks are rather short and far apart,
and the anterior portion is narrow, so that the general form of
the hvpostoma is more like that of Isotdus harrisi than /. gigas.
The total length is 75 mm., the greatest width, 65 mm.; length
of the body portion, 53 mm.., width, 50 mm.

The tran.sverse furrows are the impressions left by the
gnathobases of the basal joints of the legs. These gnathobases
were evidcntlv long and very heavy, but the specimen hus been
so abraded that ail details are obscured. The first six pairs of
impressions are longer and deeper than the four behind. The
first eight pairs seem to belong to the thoracic appendages, while
the last two belong to the pygidium. From the posterior tips
of the hvpostoma to the first gnathoba.ses of which traces are
present there is a distance of about 22 mm. without impres.sions.
In holelui gigas the hyj)0.stoma normally extends back to the
posterior margin of the cephalon, so that it seems that in this
specimen the impressions of the first two pairs of gnathobases
under the thorax may not have been preserved. T > that case,
the six pairs of strong impressions may represent the last six
pairs of thoracic .segments, and the pygidium might begin witii
the first of the fainter ones.

Two specimens of Isoielus, somewhat siniilarlv preser\-ed.
have been figured. One is Billings' specimen from ihe Trenton
at Ottawa, and the other was described by Mickleborough and
by Walcott from a specimen found near Cincinnati. Both of
these specimens, howe\er, show the trilobite itself, as well as
the impression. Both show the long heavy gnathobases of the
coxopodites, and it becomes evident that, as the coxopodites
are attached directly under the dorsal furrows, the increase in
the width of the thoracic lobe, which is so marked a feature in
Isoielus, is due to the great development of these gnathobases.
The writer believes that this impression on the ripple-marked
sand of the Chazy gives a clue to the development of the gnatho-
bases. Apparently Isotdus was a bottom crawler, and the
gnathobases may have served as ambulatory appendages. In
both the specimens of Isotdus mentioned above as retaining the
appendages, the gnathobase of a thoracic appendage is nearly
as long as the remainder of the appendage, and being a single
rod, and not jointed, is much more useful as a lever. On all the
specimens known, the gnathoba.ses are strongly developed on
the thorax, and only feebly so on tl^e pygidium. Beecher found

?fe-!l

-^Wi*"

1910]

The Ottawa Naturalist.

133

Mm

that the appendages under the pygidium of Triarthtis were
flattened and adapted for swimming, while those under the
thorax covild be used either in swimming or crawling. It would
seem .hat this sort of vSpecialization had gone still further in
Isotelus than in Triarthus. Here there is a large pygidium,
probably provided with swimming organs (Walcott found traces
of them under the pygidium of the specimen he described), and
under the thorax the inner portions of the appendages were
strengthened to function as ambulatory- appendages. In Tri-
arthus, a form adapted primarily for swimming and secondarily
for crawling, the appendages are very long, and extend far
beyond the outer margins of the test, while in Isotelus the
appendages are hardly long enough to reach the outer margins.
The swimming power had to some extent beer sacrified in the
adaptation to crawling. Triarthus depended on its swiftness in
swimming to escape from its enemies, and lacked the power of
enrolment. Isotelus, a slower moving, but heavier-shelled
animal, protected itself by complete enrolment.

it

.V

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t

PiK. 3. Diagram of the trails on a slab of
sandstone t'ound at Deschenes. 1 is the trail shown
in the photograph on the plate, and 1 and 3
are supposed to have been made by an iMotelua.

t

Certain trails found by the writer on the surface of slabs
of sandstone from the Chazy at Deschenes tend to confirm the
suspicion that the gnathobases were used as ambulatory organs.
A diagram and photograph of one of these trails is here repro-
duced, and it will be seen that it is exactly the sort of marking
that would theoretically be produced by a trilobite which was
crawling with the aid of the gnathobases only. The trail num-
bered I in the diagram can be traced for about 100 mm. on the
slab, and consists of a series of pairs of approximately parallel
ridges, arranged on opposite sides of a narrow furrow. The
ridges are inclined at angles of from 30 to 60 degrees to the
direction of the furrow. Each ridge is about 10 mm. long, and
the furrow is from 3 to 5 mm. wide. The slab is a mould of the

134

The Ottawa Naturalist.

[Nov.

impression made in the sand, and the ridges correspond to the
depressions made by the gnathobases. The t—il numbered 3
is similar to the one described, but the one numbered 2 is of a
different sort.

The increase in width of the axial lobe, caused by the de-
velopment of the gnathobases in the adaptation to the crawling
mode of life, explains the parallelism which exists between certain
genera of the Asaphui<£, and the parallelism between Nileus
and some of the Itluanida;. A number of forms, arising from
different stocks, were becoming adapted to near-shore life, and
all fovmd that enlarged gnathobases assisted them in their new
mode of life. Thus the narrow-axised Asaphus produced Oncko-
metopus, Isoteloidi's produced hoielus, and Symphysurus de-
veloped into Mleus, just as some as yet unknown form developed
into the Illcenurus of the sands of the Potsdam.

Locality. — This species is represented in the collections
at the Museum of the Geological Survey by a thorax and
p\gidium from Deschenes, and a free cheek from Britannia, which
are holotvpe and paratype respectively. There is also a partial
thorax and pvgidium collected by James Richardson in 1853
from the sandstone of the Chazy at West Hawkesbury. The
pygidium of this specimen is 72 mm. long and about 110 mm.
wide, and shows a .single rib on each pleural lobe. The axial lobe
of the thorax is very narrow, being only 35 mm. in width. The
total width appears'to have been somewhat over 100 mm. The
fourth specimen was found loose at Point Claire, but was un-
douMedlv from the Chazy, which outcrops there. This speci-
men shows the posterior portion of the hypostoma and portions
of six thoracic segments. The forks of the hypostoma are very
shorv. and the bodv portion is convex. The axial lobe of the
thorax is 53 mm. wide, and the total width of the thorax is
160 mm.

EXPLANATION OF PLATE II.

1. Bathvurus supcrbus Raymond. A small cranidium.
About natural size.

2. The same species. An imperfect thorax and pygidium.
Slightly smaller .han natural size.

3. The same species. A nearly complete specimen. About
natural rize.

4. Trail, supposed to be that of an hotclus.

5. Impression of the ventral surface of a trilobite, presum-
ablv Isotelus arcnicola. About one-fifth natural size.

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