[MATTHEW] CAMBRIAN FAUNAS 101 
A circumstance affecting this comparison is that more abundant 
collections were made from the Etchemin terrane than from the 
Coldbrook, and as the size of the largest valves is recorded in the 
description of the species, this would give the Etchemin species an 
advantage as regards comparative size. But even after eliminating 
this possible occasion of a greater than the natural difference, there 
remains enough variation to prove an increase in size of the Brachio- 
pods as time went on. 
For the purpose of checking this result, an examination was 
made more in detail of the last four of the genera named above, 
as they are represented by species in the Etcheminian terrane, from 
which it will be seen that an increase in size is noticeable in all these 
genera, as they pass through the Etchemin terrane. The assise where 
each species occurs is given in the margin of the following table. The 
assises occur in the following order from below upward, the Coldbrook 
being the lower terrane. 

Co: FOSSILIFEROUS } CoLDBROOK 
SHALE OF THE TERRANE 
la | 
16 
oe Division 1 
ld 
le 
2a 
2b + LE 
Division 2 Etchemin Terrane 
2c 


Lower Fauna 
3a 
36 
-3¢ 
34 
3e 
3 f 
———_—s i” 
Division 3 
Upper Fauna 

nn 
~ 

The fauna of the two lower divisions of the Etcheminian is 
distinct by its species from that of the upper division, and to some 
extent also by the genera. 
