396 FOSSIL EYES OF TRlLOBFrES. 
retained in the living Branchipus, nor should 
the primeval form of Limulus have possessed 
such an intermediate character, or have re- 
mained unadvanced 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 Tri- 
lobites 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 af- 
fords the most ancient, and almost the only 
* The very rare fossil engraved in Martin's Petrifacata Derbi- 
ensia (Tab. 45, Fig. 4,) by the name of Entomolithus Monocu- 
lites (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 be- 
tween the Trilobite and living Crustaceans. — Geol. Trans. N. S. 
vol. i. p. 208, PI. 27. 
