220 HOMOLOGIES. 
groups were wanting that are most prominent in 
modern geological periods, those that existed 
were expressed in such endless variety that the 
Animal Kingdom seems to have been as full then 
as itis to-day. The Class of the Echinoderms is 
one of the most remarkable instances of this pe- 
culiar distribution. In the Silurian period, the 
Crinoids stood alone; there were neither Ophi- 
urans, Asterioids, Echinoids, nor Holothurians ; 
and yet in one single locality, Lockport, in the 
State of New York, over an area of not more 
than a few square miles, where the Silurian de- 
posits have been carefully examined, there have 
been found more different Species of Echino- 
derms than are living now along our whole 
Atlantic coast from Maine to Florida, where we 
find representatives of all the five orders of the 
class. 
There is nothing more striking in these early 
populations than the richness of the types. It 
would seem as if, before the world was prepared 
for the manifold existences that now find their 
home upon our earth, when organic life was 
limited by the absence of many of the physical 
conditions now prevalent, the whole wealth of 
the Creative Thought lavished itself upon the 
forms first introduced upon the globe. After 
thirty years’ study of the fossil Crinoids, I am 
every day astonished by some new evidence of 
