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 it is 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 



