TRILOBITES, THEIR DISTHIBUTION. 389 
mencements of the history of fossil Crustaceans, 
I proceed to select one very remarkable family, 
the Trilohites, and to devote to them that detailed 
consideration, to which they seem peculiarly en- 
titled, from their apparently anomalous struc- 
ture, and from the obscurity in which their history 
has been involved. 
Trilobites. 
The great extent to which Trilobites are dis- 
tributed over the surface of the Q:lobe, and their 
numerical abundance in the places where they 
have been discovered, are remarkable features 
in their history ; they occur at most distant 
points, both of the Northern and Southern Hemi- 
sphere. They have been found all over Northern 
Europe, and in numerous localities in North 
America ; in the Southern Hemisphere they occur 
in the Andes,* and at the Cape of Good Hope. 
ence at this early period of a crustacean approaching to Pali- 
nurus, and as large as our common Sea Crawfish. 
Two other specimens exhibit the breathing organs of another 
delicate Crustacean, with the tips of the four larger and four 
smaller branchiae preserved, and pointing towards the region of 
the heart, showing that these fossil Crustaceans belonged to the 
highest division of the Macroura. They reminded Mr. Broderip 
of the living Arctic forms of the macrouroiis decapods. 
* I learn from Mr. Pentland that M. D'Orbigny has lately 
found Trilobites accompanied by Strophomena and Producta in 
the Greywacke slate formation of the Eastern Cordillera of the 
Andes of Bolivia. Fresh water shells, Melania, Melauopsis, and 
probably Anodon, occur also in the same rock; a fact which 
