44 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



Gallery X. resemble in the simple mouth and absence of mesenteries ; 



others place them with the Anthozoa, which they resemble 

 in the origin of the reproductive cells. Other features, 

 however, distinguish them from both these Classes. 



Class SCYPHOZOA. 



Many Coelentera being soft-bodied animals can leave no 

 fossil traces except impressions that they may have formed 



Fig. 18. — A fossil jelly-fish, Bhizostomites lithographiciis, one of the Scypho- 

 medusae, from the Kimmeridgian of Solenhofen. a, imprint on the 

 exposed surface of the Lithographic Stone, about ^ natural size. (From 

 E. Ray Lankester's "Extinct Animals." After Walcott.) b, diagram 

 interpreting the marks seen in a. (After Brandt.) c, diagram to show 

 how the imprint is formed by the jelly-fish settling down on the mud ; 

 a vertical cut has been made through the mud and through the middle 

 of the jelly-fish. (After Walcott.) 



on a sandy shore ; these of course can only be left by free- 

 swimming jelly-fishes or medusae, not by fixed forms. Such 

 impressions are actually known in various rocks from the 



