IX. 



EVOLUTION OF FOSSIL CEPHALOPODA. 

 By James Perrin Smith. 



Most of the paleontologic contributions to the evi- 

 dence of evolution were gathered before the time of 

 Darwin, and are therefore all the more 

 General evidence trustworthy because the naturalists that 

 pa eon o ogy. g^j.j^gj.ed them were not evolutionists. 

 It is indeed remarkable that their classifications have 

 been so little changed by the introduction of the theory 

 of evolution into the study of biology. Since this is the 

 case the paleontologic record ought to show the order 

 of appearance of genera in time, and their genetic rela- 

 tionship. It does do this in a general way. Thus in 

 the echinoderms we have the cystoids, apparently the 

 primitive stock, beginning in the Cambrian and disap- 

 pearing in the Carboniferous; the blastoids, somewhat 

 higher, began in the Upper Silurian and disappeared in 

 the Carboniferous; the true crinoids, or sea lilies, began 

 in the Lower Silurian and survived until the present day. 

 Asteroids we know from the Cambrian on, and echinoids, 

 or sea urchins, from the Lower Silurian until now. 



Although their succession in time suggests genetic 

 relationships, the crinoids, and especially the cystoids, 

 being the most primitive type, the first known of the 

 three great groups are apparently as widely separated 

 from each other as they now are. Either they are par- 



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