FOSSIL EYES OF TRILOBITES. 299 



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 Trilobite still retained in the living Branchipus, 

 nor should the primeval form of Limulus have possessed 

 such an intermediate character, or have remained unad- 

 vanced in the scale of organization, from its first appearance "■ 

 in the Carboniferous Series,* through the midway periods 

 of the secondary formations, unto the present hour. 



Eyes of Trilohites. 



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 in- 



* Tlie 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 collectien 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 Trilo- 

 bite from Lake Huron (PI. 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,PI.27. 



