This genus derives its name from the Greek word Ασαφης--obscure. It
embraces perhaps more species than any other genus of the family of
trilobites. About twenty have already been discovered. Most of them
are very characteristic and can easily be determined, but as the genus
Asaphus, is intermediate between Calymene and Ogygia, it is sometimes a
little difficult to decide the genus to which the inosculating species
on each side, belongs.
In general, the Asaphs may be known by the body being very much
depressed, and by the membranaceous development, which extends beyond
the lateral lobes. The middle lobe of the abdomen, is rarely more
than one-fifth the width of the body. As the abdomen and tail of the
Asaph are the only portions of the animal commonly found entire, the
distinctive characters of the genus above given, may generally be
ascertained.
Professor Brongniart remarks, that the ribs of the _Asaph_, which
correspond in number and position to the articulations of the middle
lobe, "are sometimes simple or undivided, at least in the post abdomen,
but that they are always bifurcated in the _Calymene_" As far as our
observations have extended, these remarks do not apply either in the
one case or the other.
The head or buckler of the _Asaph_, is not so deeply divided into
three lobes as the _Calymene_; they are, however, quite distinct. The
oculiferous tubercles are in some species exceedingly well marked by a
reticulated structure.
This genus often occurs at the same localities with the Calymene,
though in some instances it seems to occupy rocks peculiar to itself.
Dr. John Bigsby, in his list of organic remains occurring in the
Canadas, states, that he never found a single species of the genus
Calymene, on the north side of the River St. Lawrence, although
the Asaphs were very abundant.[23] In his Sketch of the Geology of
the Island of Montreal, he however observes: "Of Trilobites, the
Asaph genus is the most abundant, they approach nearest the species
_caudatus_, of Brongniart. I have found no entire Calymene, but many
bucklers or heads of the Blumenbach species, some of them an inch and a
half in diameter. They are found whole in considerable numbers in the
vicinity of Quebec."[24]
[Footnote 23: Silliman's Journal, vol. viii. p. 83.]
[Footnote 24: Annals New York Lyceum, vol. i. p. 214.]
Asaphus Laticostatus.[25] _Green._ Cast No. 13.
[Footnote 25: From the Latin for "broad ribbed."]
Cauda prælonga, pars ad marginem vix membranacea; cute coriacea,
tuberculis minimis; costis latis, convexis et valde distinctis.
The fragments of this species, which we have examined, comprise ten
articulations of the middle lobe, and the corresponding ribs of the
sides, all in a very good state of preservation; the extent to which
the membranaceous expansion reached beyond the tail and the lateral
lobes is very apparent, but it has been unfortunately broken off all
round. Our specimen appears to be a natural cast of the internal part
of the shell, or the coriaceous covering of the animal.
The portion of this specimen of trilobite which still remains perfect,
is two inches long, and three inches and a quarter broad. The middle
lobe exhibits the appearance of a very exact and gradually tapering
cone, its articulations being rounded and slightly flattened on the
top. The ribs of the lateral lobes are nearly straight, slightly
arched, broad, rounded, and gradually increase in width from the point
of their insertion; they are simple or not bifurcated throughout, and
are covered with very minute granulations, which are probably produced
by the sandstone in which the animal is mineralized. The membranaceous
expansion near the caudal termination, is a good deal prolonged.
The A. Laticostatus occurs in a light coloured ferruginous sandstone,
which contains a multitude of other fossil remains, particularly
a large species of Productus and of Terebratula. It is said to
have been found in Ulster county, in the State of New York, by the
late Charles Wilson Peale, Esq., the distinguished founder of the
Philadelphia Museum. During the memorable search after the bones
of the _Mastodon Giganteum_, in the marl pits of that county, this
enterprising naturalist procured our Asaph with many other remarkable
petrifactions. The rocks which contain them were probably found not
_in situ_, but were masses rolled from the neighbouring Shawangunk
mountains,[26] which by some geologists are supposed to be a link in
the grand chain of the Alleghanies. Mr. R. Peale, of New York, lately
visited the rich repository of fossils in Ulster County, and procured a
number of specimens of the A. Laticostatus, all of which he has kindly
permitted me to examine. These are much smaller than our cast, but in
many instances the caudal elongation is perfectly developed. The A.
Laticostatus also occurs in the Helderberg mountains, specimens of
which are in the Albany Institute.
[Footnote 26: The Lenape tribe of Indians, who formerly inhabited this
district of country, gave the name of Shawangunk to this stupendous
ridge of hills a name which has been very properly preserved.]
Asaphus Selenurus.[27] _Eaton._ Casts Nos. 14 & 15.
[Footnote 27: Derived from _Selene_, moon, and _ouros_, tail.]
Cauda semilunari; costis angustis, valde distinctis; abdominis
articulis duodecim; corpore convexo.
I am indebted to Professor Eaton, for two specimens of this very
interesting species. In his Geological Text Book, he thus describes
it: "Tail crescent-form, or concavo-convex, with the convex side
forward, upon which the post abdomen terminates: abdomen contains
about 12 articulations, with an abrupt termination equal in breadth
to one-fourth of the length of the transverse lunate tail; the
articulations of the side lobes gradually incline towards the axis
of the body, until the last pair terminate at the tail. Found in
transition limestone at Glenn's Falls, and Becroft's mountain, near
Hudson. I have a specimen from Becroft's mountain, with part of the
original covering of the animal remaining."
When we first noticed the remarkable lunate appearance of the tail
of this Asaph, we supposed that it was occasioned by some accident,
but there seems no doubt that this conformation is natural. In
our specimens of this species, which are not however perfect,
the articulations of the abdomen do not exceed 8 in number. The
representation of this animal remain given by Mr. Eaton, plate 1,
figure 1, is exceedingly inaccurate; it will confuse rather than
illustrate the subject. Our cast and the drawing, we believe, are taken
from the same specimen, which was kindly loaned by Mr. Eaton for this
work. It is but justice to the amiable, industrious, and indefatigable
author of the Geological Text Book to remark, that he regrets as much
as any one, the insufficiency of his figures of the trilobites, to give
any correct idea of the fossils they are intended to represent.
In the cabinet of the Albany Institute there are a number of specimens
of the A. Selenurus. One of our models represents the natural mould
made by the animal in the rock; the other is an impression taken from
it, in order to exhibit the animal in a more satisfactory manner.
Asaphus Limulurus.[28] _Green._ Cast No. 16.
[Footnote 28: From two Greek words, which signify "Limulus tailed."]
Cauda longa, spina munita sicut in Limulo; costis abdominis in
spinis retrorsum flexis, desinentibus.
It is very much to be regretted that the abdomen and caudal end only of
this remarkable Asaph have hitherto been discovered; it is, however,
exceedingly gratifying that the fragment still remains in so perfect a
state. It forms a part of the magnificent cabinet of organic remains
belonging to J. P. Wetherill, Esq., now deposited in the Academy of
Natural Sciences, of Philadelphia.
Dr. J. J. Cohen discovered a small specimen of this species at
Lockport, New York, which he has presented to the Athenæum, in
Baltimore.
Eight articulations of the abdomen, and ten of the tail, are all of
this fine species that we have seen. The ribs, or costal arches of
the abdomen have a deep furrow on their upper surface, commencing
at the middle lobe, and terminating near their free extremities;
these extremities appear all detached from each other, and end in
reflected points or spines, so as to give the side of the animal a
serrate appearance. The costal arches of the tail are grooved through
their whole extent, and present no spinous terminations. Beyond the
membranaceous expansion of the tail, which is somewhat similar to that
of the Asaphus Caudatus, there projects a single spine, like that from
the tail of the _Limulus polyphemus_; this spine may be traced under
the caudal membrane to its insertion into the middle lobe. A portion
of the crustaceous shell is still entire, and it seems to have been
covered with very minute granulations. A row of large granulations
may easily be traced on each side of the middle lobe. Length of the
fragment, one inch and a half. Breadth one inch and a fourth.
The A. Limulurus was found in the dark brown, shaly limestone, at
Lockport, in the State of New York; it is associated in the same rock
with the terebratula and several other fossils.
The singular spinous projection from the tail of this Asaph, furnishes
another analogy, between the trilobite and the limulus; an affinity
which was suggested by Dr. Dekay; and which has been argued with great
ingenuity both by himself and Professor Wahlenberg.[29]
[Footnote 29: See Nova Acta Regiæ Societatis Upsalensis: 1821. Also,
Annals of the Lyceum of Natural History. New York. Vol. i. pages
179-185.]
Asaphus Caudatus.[30] _Brünnich. Brongn._ Cast No, 17.
[Footnote 30: From the Latin word for "tailed,"]
Clypeo antice subrotundato, postice valde emarginato, angulo
externo in mucronem producto; oculis exsertis, conicis, truncatis,
distincte reliculatis; post abdomine in caudam membranaceam, acutam
extenso. (Vide Brongniart.)
The middle lobe of the buckler is marked by three transverse plicæ
or folds on its posterior part, and its cheeks or lateral portions
are triangular; the posterior exterior angles of which, are acute,
and considerably elongated. The cheeks are furnished with conical,
truncated, semilunar and externally convex tubercles, which were beyond
all doubt the eyes of the animal, being reticulated as in those of
the Limulus. The middle lobe of the back is narrow, and has twelve
articulations. The lateral lobes are composed of double ribbed costal
arches. Beyond the lateral lobes and the caudal termination, there is a
smooth, thick membranaceous expansion, which forms an acute projection
below the central portion of the tail.
The specimen in the Philadelphia Museum, by which I have identified
this species, is marked as coming from Ripley, Ohio. It reposes on a
fragment of ash coloured limestone--which contains also a mutilated
specimen of what seems to be a calymene, and a few small terebratulæ,
&c.
Dr. John Bigsby, in his "List of Organic Remains, occurring in the
Canadas," states that the A. caudatus is frequently met with, thrown
up by the water on the north shore of Lake Superior--on the bank of
Rainy river--at the Lake of the Woods, and at several other places. In
some localities they are astonishingly numerous, and so small as to be
almost microscopic. They occupy indiscriminately limestone of every
colour, but are most numerous in that which is brown or crystallized.
They are composed of the kind of limestone in which they happen to be
embedded.
We have seen a number of specimens of this species in the Albany
Institute, in Mr. Wetherill's cabinet, and in the Baltimore Athenæum;
but in all of them, the abdomen and caudal extremity only remain
perfect: from their exact resemblance, however, to the same parts of
the A. caudatus, figured by Brongniart, (plate 2, fig. 4, D.) we have
no hesitation with regard to their identity. The description which
we have given of the _buckler_, supposed to belong to our Asaph, is
therefore taken from Brongniart, whose specimens were found at Dudley,
the celebrated locality of the C. Blumenbachii.[31] The coriaceous
membrane, which extends beyond the lateral lobes and forms the caudal
termination of our species, is not covered with minute dots, as in
the European fossil; and if a new name is to be applied to it on that
account, it may be called _A. glabratus_.[32] M. Wahlenberg, has given
the figure of a trilobite which he calls _caudatus_, but ours cannot
be mistaken for that species, to which Brongniart has very judiciously
applied the name of _A. meucronatus_.
[Footnote 31: In the first volume, 2d series, of the Transactions of
the Geological Society of London, Mr. Weaver has published some highly
interesting observations on the fossils found in Gloucestershire,
England. The A. caudatus, he states, is there found in the transition
limestone, though very much mutilated. (Vide p. 326.)]
[Footnote 32: In the cabinet of G. W. Featherstonhaugh, Esq., I have
examined a fine specimen of the A. caudatus, from Dudley, England,
but could not perceive the minute dots on the tail, as mentioned by
Brongniart.]
The conical eye-like protuberances on the head of this species, are
very remarkable, and so much resemble the reticulated eyes of the
limulus, as to leave no doubt that they once contained the organs of
vision.