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. 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.