forms of more perfect Crustaceans may, during the lapse of ages, have been derived; but according to this hypothesis, we ought no longer to find the same simple condition as that of the Tribolite still retained in the living Branchipus, nor should the primeval form of Limulus have possessed such an intermediate character, or have remained unadvanced in the scale of organization, from its first appearance in the Carboniferous Series,[1] through the midway periods of the secondary formations, unto the present hour.
Eyes of Trilobites.
Besides the above analogies between the. Trilobites and certain forms of living Crustaceans, there remains a still more important point of resemblance in the structure of their eyes. This point deserves peculiar consideration, as it affords the most ancient, and almost the only example yet found in the fossil world, of the preservation of parts so delicate as the visual organs of animals that ceased to live many thousands, and perhaps millions of years ago. We must regard these organs with feelings of no ordinary kind, when we recollect that we have before us the identical instruments
- ↑ The very rare fossil engraved in Martin's Petrifacata Derbiensia (Tab. 45. Fig. 4,) by the name of Entomolithus Monoculites (Lunatus) appears to be a Limulus. It was found in Iron Stone of the Coal formation on the borders of Derbyshire. A similar fossil in the collection of Mr. Anstice, of Madely, is engraved in our Plate 46″, Fig. 3. In the Secondary period, during the deposition of the Jurassic limestone, the Limulus abounded in the seas which then covered central Germany; and it still maintains its primeval intermediate form in the King Crab of the present ocean. My friend Mr. Stokes has discovered, on the under side of a fossil Trilobite from Lake Huron (Pl. 45, Fig. 12.,) a crustaceous plate (f) forming the entrance into the stomach, the shape and structure of which resemble those of the analogous parts in some recent Crabs. This organ forms another link of connexion between the Trilobite and living Crustaceans.—Geol. Trans. N. S. vol. i. p. 208, Pl. 27.
