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BSERVATIONS

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OBSERVATIONS

ON THE

TERATASPIS GRANDIS, Hall.

THE LARGEST KNOWN TRILOBITE.

By J. M. CLARKE.

OBSERVATIONS ON THE TERATASPIS GRANDIS, Hall,
The Largest Known Trilobite.

By J. M. CuarkeE.

Communicated to the State Geologist December, 1890.

Trilobites of great size have been reported from various forma-
tions. With rare exceptions, however, these relics are but fragments
of the test, leaving to the imagination the restoration of the original
proportions of the animal, and without an earnest mental effort one
is apt to leave the contemplation of the large fragment with no ade-
quate conception of the imposing lineaments of its owner. Indica-
tions of these gigantic forms occur in all the grand faunas of the
Paleozoic, with the exception of the Carboniferous where diminution
in numbers was accompanied by diminution in size, or, in other words,
by the prevalence of genera in which great size was never attained.

Almost with the earliest known appearance of the Trilobites the
genus Pasrapoxipes attained magnificent proportions. Paradoxides
Harlan, the well-known species of the Braintree argillites, must have
grown to a length of 18 inches. Anaettn has figured an entire speci-
men of P. Tessini 12 inches in length, and Barranve a fragment of an
individual of P. imperialis which must have had about the same size.
Mr. G. F. Marruew has described a nearly entire individual of an
immense P. regina from the St. John beds, 15 inches long and 12
inches across the base of the cephalon, and it is claimed, with
undoubted accuracy, that this is the largest undismembered specimen
of a trilobite found in any country.

In the second faunas great Asaphids were not uncommon. As
early as 1839 Dr. Joun Locke described in the report of the Geological
Survey of Ohio, a portion of an immense pygidium to which he gave
the name /sotelus maximus. In 1843 Dr. Locke figured an entire indi-
vidual of what he considered the same species, changing the name,
however, to Jsotelus megistus. ‘This specimen measured nine and three-
quarters inches in length. The figure was accompanied by outlines
of two large pygidia, the greater of which was that referred to in 1839,
which, the author says, coincided “ with the end of an ellipse 22 inches

4

”

long and 12 inches broad.” This is an evidently much compressed
fragment, measuring seven inches in its greatest transverse diameter,
and assuming this as the greatest diameter of the pygidium and
restoring the length from the proportions of the animal as there
given, the original length of its owner would have been about 13
inches. The plate is incomplete on its anterior portion, and it is
probable that the error in this estimate due to the exaggeration of
size from compression of the shield, is compensated by the loss of
diameter from imperfect retention. This great pygidium, with other
large fragments of the same species, were used as a basis for a well-
known restoration in plaster to be found in some of the older muse-
ums of this country. ANncELIN has given a restoration of Megalaspis
heros 14 inches in length and Broacezr estimated the original length of
Megalaspis acuticauda to be fully 16 inches. Barranpz figured an
entire Asaphus nobilis from Etage D which measures 10} inches.

Not until the introduction of the genera Datmantres, HomaLonotus
and Licuas do we meet with the most gigantic proportions attained
by these crustaceans, and then only after these genera have become
well established. Perhaps none of their representatives in the lower
Silurian faunas were of commanding size; in the upper Silurian large
but not extravagant proportions were sometimes attained. Lichas
Boltoni of the Niagara fauna, is a magnificent species, one of the
largest of its race and remarkable for the frequency with which its
parts are found together, an extremely uncommon occurrence in this
thin-shelled group. The Lichas pustulosus of the Lower Helderberg
shaly limestone was a great species attaining a length of 10 inches or
more. Homalonotus delphinocephalus of the Niagara fauna grew to
large size but does not appear to have attained the length of its suc-
cessor in the Lower Helderberg, H. Vanuxemt, which, according to the
restoration from a very large fragment given in the Paleontology of
New York, Volume VII (plate V B) grew toa length of at least 11}
inches. Satter has mentioned (Paleontographical Society, vol. xvii,
p- 109) a large fragment of Homalonatus rudis which he estimates may
have been a foot in length. In later faunas are found traces of this
genus of still greater size. Dr. Beusnausen has figured a pygidium of
H. gigas from the Spiriferen-sandstein of the Hartz, the possessor of
which must have been upward of one foot in length. Unquestion-
ably the largest individual of Homatonotus known is that of H. major,
from the Oriskany sandstone, figured in the Paleontology of New
York, Volume VII (plate V A), a large fragment representing the
greater part of the thorax and the pygidium, and according to the
restoration there given the original length of the animal must have

5
been well nigh 15 inches. The later and common Hamilton species,
Hf. DeKayi, attained no extravagant size though frequently large, e. g.
the enrolled individual figured on plate IV (op. cit.), the largest entire
specimen reported, which is about 9 inches in length; some large
fragments indicate that the animal was sometimes as long as 11
inches. :

The size attained by some of the Devonian species of Dat-
MANITES and their immediate predecessors was marvelous. The
pygidium of PD. micrurus figured in the Paleontology of New
York, Volume III, page 359 (there given as D. pleuroptyx), indicates
an individual at least 11 inches in length, and there is reason to
believe that the Lower Helderberg species, D. nasutus and D. tridens,
attained a size fully as great. Most remarkable however is the great
pygidium of D. myrmecophorus of the Corniferous limestone, figured
upon plate XV of Volume VII (op. cit.), which from the restoration
there given, made from careful comparative measurements, would
imply an individual 16 inches long.

An interesting feature of the early Devonian trilobitic faunas is
the reappearance of Catymenr in the Schoharie grit and Corniferous
limestone, a fact which has been duplicated by the recent
description by Dr. Ornterr of a large species (C. reperta), from
the lower Devonian of Saint Malo in Angers. The American
Devonian species, C. platys, is not only the latest but the largest known
representative of the genus, and for a group which at its maximum
development in species and individuals in the Silurian, rarely attained
considerable dimensions, the proportions reached by C. platys are
especially ndteworthy. The entire individuals on plate 1 of Volume
VII of the Palzontology show this, and the restoration accompanying
a very large pygidium on plate xxv, if accurately drawn, indicates
that a length of upward of eight inches was sometimes attained by
the species.

No larger or more extravagantly ornamented trilobite than the
Terataspis grandis, Hall, is known. This giant of its race has left
fragments of its test in the Schoharie grit of eastern New York, and
in the commingled Schoharie and Cornifercus faunas of the Province
of Ontario. A very complete illustration and discussion of its differ-
ent parts, are given in Volume VII of the Paleontology (p. 73, pls. xvii,
XViii, xix), and from these one readily obtains an idea of the structure
of the cephalon, thorax and abdomen, the free cheeks alone being
there unrepresented. There is, however, a very large free cheek in a
fragment of Schoharie grit in the collection of the American Museum
of Natural History, which in all probability belongs to this species.

6
At the time of the preparation of this volume of the Paleontology of
New York, the original specimen of Mr Brturnas’ species Lichas
superbus, was made accessible for study by the kindness of the Director
of the Geological and Natural History Survey of Canada. This
specimen is a portion of the cephalon and a pygidium of Terataspis
grandis, lying in juxtaposition on the same block, there being no
doubt of their having belonged to the same animal. From this speci-
men it was possible to establish the relative proportions of cephalon
and pygidium in this species, and from the data furnished by all the
material under study, with careful comparative measurements of entire
specimens of Licuas in the collections of the State Museum, and of
figures of such specimens as have been given by ANGELIN, BARRANDE
and Scumipt, the accompanying reproduction of the original size of
the animal has been drawn, its base being the largest and most com-
plete cephalon figured in the work cited (pl. xvii, fig. 1; xviii, figs. 1, 2).

This restoration gives to the proprietor of this cephalon a length of
nearly 20 inches. The figure does not however do full justice to
the proportions of the animal. In the cephalon which has served
as a base for the restoration the great ovoid central lobe of the
glabella has a length of 2} inches. Mr. Bituinas speaks of a
specimen of Lichas superbus in which the length of this lobe was fully
3 inches. If the increase in size of this part was accompanied by
the same relative increase in the size of the entire animal (and there
is no good reason for assuming the contrary), such a fragment would
represent an individual fully 24 inches in length, a size unsur-
passed and unequaled by any other known trilobite.

With his extravagant armor of defense and aggression, Terataspis
grandis must have been easy lord of his invertebrate domain and no
very palatable morsel for the heavily plated fishes of his day.

In the genera Puacors and Prortus great size was never attained.
The earlier forms of both of these genera were of inconspicuous pro-
portions and their maximum size was attained in the middle Devonian.
An entire Phacops rana is figured in the Paleontology of New York,
Volume VII, which has a length of 4 inches, and cephala in the
Museum collection indicate an original length of 5 inches, perhaps
the greatest size which has been observed in this genus. Prorrus has
a still smaller habit, that is, its maximum size is never so great, and,
probably, the largest example of the genus recorded is represented
by a cephalon of Proetus macrocephalus from the Hamilton group,
which belonged to an individual fully 33 inches in length.

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