122 AN INTRODUCTION TO THE STUDY OF FOSSILS 



become filled with fine sand or mud; this mud or sand filling 

 becoming covered by other mud before the soft jelly-fish body 



A B 



Fig. 45. — A fossil jelly-fish, Brooksella alternata Walcott, from the Middle Cambrian 

 of Coosa Valley, Alabama. A, top view showing the nine lobes and a trace of the 

 furrow in the ring about the central disk ; B, under view of same specimen. The 

 lobes are shown, as also are what appear to be oval arms (.v) for carrying food to 

 the central stomach. A central depression (a') may represent the position of 

 the mouth. Natural size. (After Walcott.) 



has become disintegrated preserves the outline of its contain- 

 ing cavity (Fig. 45). 



Derivation. — Scyphozoa > Greek scyphos, cup, + zoon, ani- 

 mal, referring probably to the inverted cup-like appearance of 

 the swimming jelly-fish. 



CLASS C, ANTHOZOA (CORALS) 



Type of class, Astrangia danoe (\\\'mg) (Fig. 46). 



This is a colonial form, with the individuals, — the polpys, — 

 in sessile, star-like cups encrusting stones, dead shells, etc. 

 Living and active it looks much like a tuft of white, translucent 

 moss ; after death and the decomposition of the flesh nothing is 

 seen but a calcium carbonate mass (one-half to three inches 

 in diameter) of star-like cups (corallites), each with a diameter 

 of three to five millimeters. 



It lives in shallow seas off the coast of North America from 



