Genus Paradoxides. Brongniart.
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.