The Evolution and Classification of the Genera 
of the Brachiopoda. 
In the foregoing pages, a consecutive account of the characters 
of the various genera of the Brachiopods has been given, without 
attempting to interrupt it with broader designations and group- 
ings. Ina work of this nature, such a consecutive narration of 
the genera is necessary, though wholly conventional and 
unnatural. The development of these animals throughout 
geologic time has not been along an undeviating line, but, on the 
contrary, isa series of departures at different periods in their 
history, from various comprehensive and prolific stocks. The 
courses of their existence can be expressed only by divergent and 
ramifying lines branching off here and there at rapid intervals 
during the vigor of the race, the off-shoots becoming more and 
more unlike as their growth continues, at times terminating 
abruptly as though unfavorable conditions had put a period to 
their existence, but usually in their prolonged existence and 
gradual decline resuming many of their early parental traits. 
As a preliminary and general principle, it must first be 
observed that, in the development of any great race of organisms 
(always exemplified by those whose history is known for such 
an illimitable period as the Brachiopoda) the specialization of 
generic characters and the evolution of distinct generic stocks is 
carried on with much greater rapidity during their early 
existence than at any time in their later history. The primitive 
types embody the potentialities of all subsequent expressions 
which the race assumes. 
It then becomes a question of elementary importance to ascer- 
tain these primitive generic types and to fix upon the radicle or 
root-stock from which all lines of evolution in this group have 
departed. With our present knowledge, it is believed possible 
to approximate these starting points in the history of the race 
with some degree of accuracy. Before, however, proceeding to 
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