‘AND DISTRIBUTION OF TRILOBITES. PL 
III. On the Distribution of the Trilobites in the Strata. 
The Trilobites belong to the oldest class of animals that we 
are acquainted with; they are restricted to the first of the three 
principal groups into which we may arrange the long series of 
fossiliferous formations, namely to the paleeozoic rocks. As- 
sertions of the discovery of this class of animals, both in the re- 
cent state and likewise in the younger strata, have been made, 
but every one of these statements has proved to be unauthenti- 
cated and erroneous. The newest deposits in which they have 
hitherto been found to occur is the lower coal formation, the 
fundamental rock of the coal beds, the mountain limestone of 
the British Islands, and the equivalent strata of the continent. 
No trace of them has as yet been discovered in the Zechstein 
formations: for that which Von Schlotheim described as Tri/. &i- 
tuminosus are the gum-teeth of a fish (Janassa), as was subse- 
quently recognised by Count Miinster, who gave a more accu- 
rate representation of them. Lower downwards, however, they 
have been found through almost all the subdivisions of the trans- 
ition rocks. Within these limits, which, comparatively speak- 
ing, are restricted, they are found widely distributed throughout 
the known earth, abounding in species and genera, at many lo- 
calities in almost inconceivable numbers. They belong therefore 
to the most important inhabitants of those oceans in which the 
subdivisions of the palzeozoic rocks were deposited. The struc- 
ture of their eyes, which entirely corresponds with the structure 
of that organ in recent marine Articulata, affords us a proof that 
the water of those oceans and the supernatant atmosphere must 
have been equally as transparent a medium at that time as it is 
at the present day, and that therefore no material permanent 
alteration can have resulted in either during the thousands of 
years which have elapsed since the creation of the animal world 
on this earth. 
It is perhaps well to commence with the Trilobites in the pa- 
leozoic rocks in the countries surrounding the Baltic. 
1. Countries adjacent to the Baltic.—The succession of strata 
of the different subdivisions of the transition rocks is nowhere 
so evident and striking in any part of the globe as in the 
countries on the Baltic. It need not be matter of surprise 
| therefore that Linnzus (in his ‘ Journey through West Goth- 
land, 1765, p. 21, &c.) makes us acquainted with the entire 
