The fossil remains of the trilobite family, are supposed by most naturalists to belong to a race of beings now extinct; but from the strong analogy which exists between them and certain species of crustaceous animals now living, it is highly probable that they will yet be found alive. This opinion will not be regarded as visionary, when it is recollected how large a portion of the surface of the earth is still unexplored by its enlightened and civilized inhabitants--how small the number of animated beings are yet known to the scientific world--and above all the fact, that many animals as confidently declared to be peculiar to a former world, are now found to be among the creatures at present in existence. This opinion, we think, is quite as plausible, and far more interesting, than the blank and unsatisfactory hypothesis that all the trilobites are confined to an order of things before the present glorious creation.[7] [Footnote 7: The incorrectness of the inference that all the genera and species of fossil animals found in the transition rocks must be now extinct, will appear from the following extract from Bakewell's Geology:--"The _Madrepora stylina_, so common in transition lime-stone rock, is entirely wanting in the secondary and tertiary strata, but a living animal of this species has been recently discovered in the South Seas. The Pentacrinus makes its first distinct appearance in the lias; but is not frequently met with in the upper strata, and disappears entirely in the uppermost formations: hence it was long supposed that the species was extinct. A living Pentacrinus has recently been discovered in the West Indies, and its stem and branches in a perfect state have been sent to this country." (England.) In the Museum at Albany, N. Y., I have examined a recent Pentacrinus, which I conclude, came from the West Indies, from the proprietor's account of the manner in which he obtained it. It has been a very perfect specimen but the branches are gradually dropping off.] There appears to have been known to naturalists, when the improved edition of Prof. Brongniart's work on the trilobites appeared in 1822, but 17 well marked species, and out of which he constructed the five following genera, which he thus characterizes. _Genus First._ Calymene. _Body_ capable of contraction into nearly a semicylindrical sphere. _Buckler_ with many tubercles or folds. Two reticulated eye-shaped tubercles. _Abdomen and Post-abdomen_ with entire edges. Abdomen divided by 12 or 14 articulations. No elongated tail. _Genus Second._ Asaphus. _Body_ broad and rather flat. Middle lobe prominent and very distinct. _Flanks or lateral lobes_ each double the size of the middle lobe. _Submembranaceous expansions_ extending beyond the lateral lobes. _Buckler_ semicircular, with two reticulated eye-shaped tubercles. _Abdomen_ divided into 8 or 12 articulations. _Genus Third._ Ogygia.