FOSSIL MEDUSA. 



The known geologic and geographic range of fossil medusae is shown 

 in the following table: 



Table showing the known geologic and geographic range of fossil medusae. 



List of species occurring at each horizon: 



Semseostomites zitteli. 

 Eulithota fasciculata, 

 Acraspedites antiquus. 

 Rhizostomites admirandus. 

 Rhizostomites lithographicus. 

 T . Leptobrachites trigonobrachius. 



Medusina deperdita. 

 Medusina quadrata. 

 Medusina bicincta. 

 Medusina staurophora. 

 Medusina circularis. 

 Medusina porpitina. 



Permian Medusina atava. 



r « f Brooksella alternata. 

 -5 -{ Brooksella confusa. 

 S v. Laotira cambria. 



( Dactyloidites asteroides. 

 ® Medusina costata. 

 o I Medusina priuceps. 

 ^ Medusina radiata. 



There is also to be considered the possibility that the Ordovician species 

 Bytliotrcpliis (f ) radiata Nich., from the Skiddaw slates, and Discophyllwm 

 peltatwm Hall, from the Lorraine formation, are the remains of medusae. 



Of the evolution of the medusae, the fossil forms give little positive infor- 

 mation. According to Haeckel, the Discomedusae were among the latest to 

 develop of the Acraspeda. Geologically , their representatives appear in the 



Cambrian 



