Early Trilobites of the Cambrian (Rocks — Matthew. 5 
The foregoing table shows the species found in Stage i 
of the Acadian series. No organic remains are known from 
Band (or Assise) a, and it is therefore omitted from the table; 
and to exhibit better the relations of the rich fauna of c the 
column containing it is divided. 
In this table the genera are arranged according to their ap- 
parent relationship to each other. In Group i, are placed the 
species devoid of eyes and having a thorax of a few joints only. 
Group 2, includes the genera with longer thoraces, but which 
like the first group have no visible eyes. Group 3 contains the 
smaller species which possess eyes, and group 4 the large species, 
/'. e. the Paradox ides. 
The trilobites of Group i, for various reasons are to be re- 
garded as the most primitive of the genera of this fauna. They 
have no visible eyes, the joints of the thorax are few, as in the 
first larval stages of all trilobites; and the cephalic and caudal 
shields show little change in aspect from the youngest known 
to the adult stage. Of the two sections into which this group 
is divided we cannot hesitate to give to the Agnosti the first 
place for simplicity of structure, and for the most perfect re- 
tention of embryonic features. Among these are the long nar- 
row glabella possessed by the most abundant of the early 
Agnosti, and the clubshaped glabella of another of the earliest 
types. The Agnosti are also primitive in the absence of mova- 
ble cheeks and the want of genal spines, but more especially in 
having pleural joints barely sufficient in number to enable the 
animal to fold itself together. 
This genus is highly characteristic of the Paradoxides beds 
both In Europe and America. S. A. Tullberg divided the 
Agnosti into four sections, three of which are represented in 
the beds of Stage i, of the Acadian series, and they appear here 
in much the same chronological order as in Europe. 
This priinitive genus is woi"thy of special study. In its pe- 
culiar thorax, the joints of which are simply hinged together, 
without free ends arranged for sliding one over the other, it 
differs from all its cotemporaries. Although the writer in this 
paper has grouped it for convenience with Microdiscus, the 
feature last named as well as the unchanging aspect of the 
shields In young and old examples of Agnostus separate it very 
