Cauda rotundata; cute coriacea tuberculis minimis spinulosis tecta.
In De la Beche's Geological Manual, there is a list, of the trilobites
which have been discovered in the grauwacke group of rocks. This list
we have given in our introduction. Among the trilobites he states that
the Asaphus Hausmanni has been found in the United States; as we have
not seen the species, and presuming the author to be correct in his
locality, we give the following description from Professor Brongniart.
I know, he observes, only the tail of this Asaph, but it is so
different from that of other trilobites, that I do not hesitate to
establish a particular species, upon the consideration of this part
alone. Its general form is that of a semi-ellipsis; the middle lobe
represents a very slender cone. The arched ribs of the lateral lobes
are perfectly distinct and simple. I cannot perceive in them the
slightest appearance of bifurcation. This sufficiently characterizes
the species. But that which further distinguishes it from the others,
are the small, elevated points, scattered, and of course rough
(serrés), with which the skin or epidermis is covered, resembling, in
this respect, the tail of the _Apus canceriformis_.
This fragment of an Asaph is in a homogeneous, compact, blackish
limestone, which contains no other kind of petrifaction. I know not
where it was found. It is in the cabinet of M. de Drée.
On plate 2 of Professor Brongniart's work, he has given figures to
illustrate this species; fig. 3 A. represents the whole fragment,
and 3 B. two of the ribs of the lateral lobes, magnified to show the
arrangement of the tubercles, which are very peculiar.
From the above description it will be readily perceived, that the A.
Hausmanni comes very near to the A. Laticostatus. There are, however,
many striking differences, which will be obvious to those who compare
our cast with the figures of Brongniart. The shape of the ribs, and the
tubercles upon them; the form of the middle lobe and of the interstices
between the articulations, are all peculiar to each. The elongation of
the tail in our species is alone sufficient to distinguish it. We have
always been doubtful whether the minute granulations on our species
were not produced by the sandstone in which it is petrified.
Upon what authority the A. Hausmanni has been considered as a species
belonging to the United States we cannot determine. In the valuable
and extensive cabinet of trilobites belonging to the Albany Institute,
there are a number of specimens labelled with this name by Professor
A. Eaton. If we mistake not, he mentioned to us that similar fragments
of this fossil were sent by him to Brongniart, who, we understand,
is the author of the list of trilobites found in the manual of De la
Beche. The specimens which have been examined, both in the cabinet of
Professor Eaton, and in that of the Albany Institute, are certainly
not identical with the figures or descriptions published of the A.
Hausmanni. Professor Eaton, in his Geological Text Book, at page 31,
thus describes his A. Hausmanni:--"Tail rounded, and forming the middle
of a circular arc whose centre is in the fore abdomen, near the head;
covering tubercled or spined. Found in coral rag on the south shore of
Lake Erie. Also, in its underlaying grit slate on the Helderberg." Some
other trilobites mentioned in De la Beche's list as occurring in the
United States, we have not been so fortunate as to meet.
Asaphus Pleuroptyx.[33] Cast No. 18.
[Footnote 33: From the Greek word for "grooved ribs."]
Corpore depresso; cute coriacea tuberculis minimis; costis
striatis; cauda acuta, brevi.
This species like most other specimens of this genus, in our cabinets,
is decapitated--every other part, however, appears to be in a good
state of preservation.
The articulations of the abdomen and tail, which cannot readily be
distinguished from each other, are seventeen in number. The middle lobe
is flat, and regularly tapers to an obtuse lip; it is marked on each
side with longitudinal impressed lines or little grooves. The costal
arches on their upper side have a deep and narrow channel, running
through their whole course. The costal arches of the abdomen have no
membranaceous expansion beyond their terminations; this organization
is only visible immediately below the end of the middle lobe, where it
quickly finishes in an acute point. A large portion of the crustaceous
shell remains, and is covered with distinct granulations; those on the
tail are the least obvious.
This species approaches very near the A. caudatus, but the grooves on
the middle lobe, the smallness of the costal arches, and the limited
extent of the membranaceous expansion round the lower portions of the
shell, will sufficiently distinguish it.
Two specimens of this Asaph are in the cabinet of the Albany Institute.
The one from which our cast is taken, was found on the Helderberg
mountains; it is embedded in a light grey coloured limestone shale. The
other specimen, which is much smaller, was discovered near the Genessee
River, in the State of New York. The rock in which it occurs is
identical in its constitution with the other. It contains other species
of trilobites, and a number of shells.
Asaphus Micrurus.[34] Cast No. 19. Fig. 3.
[Footnote 34: From the Greek, for "minute tail."]
Cauda attenuata, acuta; corpore valde convexo; costis striatis;
parte marginali vix membranacea.
This fine, large caudal termination of an Asaph is in the cabinet
of the Albany Institute--and it is a subject of great regret, that
all that has yet been discovered relating to this highly interesting
trilobite, is to be seen in this fragment.
There are eighteen articulations of the tail and abdomen, which cannot
be distinguished from each other. The middle lobe is composed of a
series of straight, distinct, parallel articulations, very convex
about the middle, so as to form a kind of longitudinal ridge down
the back. The costal arches of the lateral lobes are very distinct,
and are longitudinally striated or grooved on their upper surface,
particularly those near the upper part of the animal. The membranaceous
expansion is very narrow along the sides of the body, and forms a sort
of hem; below the central portion of the tail it makes a short acute
projection, which seems to be supported by a short costal elongation of
the middle lobe. Length two inches and a half.
The A. Micrurus was found in the black fœtid limestone of Trenton
Falls, by M. H. Webster, Esq., and by him placed in the rich collection
of trilobites in the Albany Institute. The limestone in which this
Asaph is embedded, is almost one entire mass of petrifactions. The
general aspect of the A. Micrurus is very similar to that of a
calymene--but judging from its structure, it could never contract
its shell into a spherical figure. Its minute tail, and narrow
membranaceous expansion round the terminal edges of the lateral lobes
are quite peculiar, and determine it to be an Asaph.
Asaphus Wetherilli.[35] _Green._ Cast No. 20.
[Footnote 35: I have named this species in compliment to my friend,
John P. Wetherill, Esq., whose magnificent cabinet of fossils in the
Academy of Natural Sciences of Philadelphia, will ever remain as a
monument of his discrimination, enterprise, and liberality.]
Clypeo postice arcuato, sulcato; abdominis articulis duodecim;
cauda vix membranacea; cute coreacea vix punctata.
The contour of this beautiful Asaph is very regularly ovate; unlike
most of the remains of this genus, the buckler is still attached
to the abdomen, though one of the _cheeks_, and a portion of the
_front_ are obscured by the rock in which the animal is imbedded. The
cheeks form spherical triangles. The oculiferous tubercles, though a
good deal defaced, seem to have been circular and not lunate, as in
the A. Caudatus. A raised, curved line passes from and over the eye,
between it and the lateral lobe of the abdomen. The central lobe of
the back is composed of twelve double joints, and that of the tail of
six single articulations; where the epidermis or shell is perfect,
all the articulations appear single. The last joint of the tail is
longer than in any other of our species. The ribs of the abdomen are
rather broad, and have a deep furrow scooped out along their upper
surface; their extremities, where they can be discovered, are detached
from each other, and terminate in reflected points, like those of the
A. Limulurus. The costal arches of the tail are delicately grooved,
and terminate in the membrane. The membranaceous expansion round the
edge of the tail is very narrow, and appears to form no projection
beyond its central part. The whole epidermis is finely marked with
granulations. Length one inch and three-fourths--breadth one inch and
one-fourth.
This interesting species was found in limestone shale, near Rochester,
in Munroe County, N. Y.; and is now in the valuable cabinet of the
Albany Institute. An accidental fissure of the rock disclosed not only
a fine specimen of both the mould and the cast of this animal, but
also another individual of the same species in contact with it. From
the peculiar attitude which these fossilized animals maintain towards
each other, they appear to have been combatants at the very moment when
the catastrophe occurred which produced their mineralization. In the
Museum of the Garden of Plants at Paris, there is a large specimen of
two fossil fish, which are supposed by many to have been destroyed and
covered with mineral matter, when one of them was in the very act of
swallowing the other. Mr. Bake well, however, who accurately examined
this specimen, is of opinion, that the two heads of the fish had been
pressed together by the superincumbent weight.