THE CAMBRIAN PERIOD 



73 



the summit of the Cambrian, is well-nigh world-wide in its distri- 

 bution and beautifully illustrates the importance of such forms 



A B 



Fig. 34 

 A Cambrian Jelly-fish, Brooksella alternata. (After 

 Walcott, from Shimer's "Introduction to the Study 

 of Fossils," permission of The Macmillan Company.) 



Fig. 33 



A Cambrian 

 Sponge, Lep- 

 tomitus zitteli. 

 (After Wal- 

 cott.) 



for purposes of correlation over wide areas. It 

 should be stated that Graptolites occur only 

 in the older Paleozoic strata. 



Anthozoans (Corals) were 

 more doubtfully present be- 

 cause the fossil forms so greatly resemble 

 Sponges (Fig. 35), but recent study seems to 

 indicate that some at least were true Corals. 

 Locally such coral-like forms were common 

 enough to form reefs. 



Echinoderms. — Of the Echinoderms the 

 very simplest class, called Cystoids, are known 

 to have existed. These were the bladder-like 

 forms, sometimes with rudimentary arms, set 

 on segmented stems. Holothuroids ("sea cu- 

 cumbers") have been found in the Cambrian 

 of British Columbia but these are of no special 

 Fig. 35 geologic importance. 



A Cambrian Sponge Worms. — Tracks and borings of marine 



or Coral, Archeo- Worms are common but no actual remains are 

 cyatnus rensse- 

 laericus. (After known. 

 Walcott.) Molluscoids. — Brachiopods, next after the 



