The animals arranged under this generic name, include the organic
remains described by Linné as Entomolithus paradoxus, and Brongniart
has given the specific appellation which the great Swedish naturalist
applied to these singular animals, out of compliment to him, though he
considers it quite inappropriate. The late Professor Dalman calls this
genus Olenus, and quotes Paradoxides as a synonyme, but the term of
Brongniart seems to have the priority, and therefore must be preferred.
The animals belonging to the Paradoxides have the body very much
depressed, and the lateral much wider than the middle lobe.
The buckler is nearly semicircular, the cheeks are destitute of eyes,
and the front is marked with three transverse furrows. This last
character is probably not a permanent one.
But the most distinguishing character, is the prolongation of the
costal arches, particularly those of the tail, beyond the membrane
which they are supposed to support; the termination of these arches
is in teeth or spines. Some species of the Asaph have prolongated
extremities to the ribs of the abdomen, but we have never seen them on
the arches of the tail.
This genus is said to comprise a great number of species, but the only
one found in North America, as far as our knowledge extends, is that
described by J. J. Bigsby, in the fourth volume of the Journal of the
Academy of Natural Sciences of Philadelphia. As we have not seen the
specimen, we add the description of it in the author's own words.
Paradoxides Boltoni. _Bigsby._ Figure 5.
Oval, blind; surface with small tubercles and striæ; clypeus rounded
before; exterior angle extending in a broad spine; abdomen fourteen
jointed; segments recurved, falcate; tail membranaceous and serrate.
The shape of this individual is oval, approaching ovate; it is
moderately flat; the whole length is five inches and four-fifths; its
breadth across the middle is four inches and nine-tenths; wherever the
cutis is not removed, it is covered profusely and irregularly with
small tubercles. The denuded portions in this specimen, for the space
of three quarters of an inch from the external margin, is, in a very
small degree, depressed, and displays a number of broken and continuous
striæ, parallel to that margin. There are no traces of organs of
vision. The buckler is nearly the segment of a circle; anterior edge,
in the present case, imperfect; it is four inches and three-fifths
broad, and one inch and one-ninth long at the centre; it joins the
abdomen by a somewhat sinuous transverse line; cheeks and front of
equal breadth; the former are flat, but rise at the sharp ridge by
which they unite with the front; they are triangular in shape; their
outer angles terminating by an acute tip. The striæ mentioned above
are here not quite parallel to the external border; the front is a
shallow depression; rounded but tapering anteriorly; it is intersected
from above on each side obliquely towards the mesial line, by a ridge
bifurcating downwards; another smaller ridge nearly bisects the front
perpendicularly.
The abdomen and post abdomen are not distinct. The abdomen exclusive
of the cauda is three inches and a half long; it exhibits fourteen
costæ varying indiscriminately from one-fifth to one-fourth of an inch
in breadth, except the three inferior ones, which are rather broader;
they occupy the whole abdomen without membranous interspaces, and are
separated by a black sulcus, not always well defined, and sometimes a
line in diameter. Each costa is canaliculated from the upper and under
angle to the tip.
The middle lobe is separated from the lateral by a shallow, rude
sulcus, which however, does not always destroy the continuity of the
costæ, as they cross it; this lobe is slightly convex, one inch and
a half broad at the top, and so continues to the sixth costa, after
which it gradually contracts, until at the bottom it is one-fifth of
an inch broad, subsiding insensibly into a flat membrane-like surface;
its longitudinal sulci pass one inch farther downwards, and expanding
a little, unite with the costæ on each side the posterior edge of the
space included by them, being dentated.
The lateral lobes are quite flat, one inch and a half broad anteriorly,
and, by gradual prolongation, become at the fourth costa one inch and
four-fifths in breadth; this dimension is maintained to the ninth
articulation, when it slowly decreases to one inch at the bottom;
the recurvature of the costæ is gentle in the upper eight, but then
decreases rapidly. Their extremities, advancing two-fifths and
four-fifths of an inch into the embedding rock, are falcate with their
raised black edges, and clearly marked points.
This trilobite was found by Lieut. Bolton, at Lockport, in the state
of New York, in the black, shaly, horizontal limestone forming the
lower part of the ravine by which the Erie canal ascends the _parallel
ridge_ of Lake Ontario. Dr. Bigsby remarks on this locality, "I am not
prepared to assign to this limestone its exact place in the series
of geological formations; it is above the saliferous sandstone, and
therefore more recent than the rocks best known as abounding in
trilobites." We have, therefore, in this instance, another fact, which
demonstrates that blind trilobites are not confined to a geological
period more remote than That which has produced the animals with
oculiferous tubercles.