244 



M. K. A. Zittel 071 Fossil Lithistidce. 



Phyletic Development. 



From the mode of life of the existing Lithistidse we may 

 fairly conclude that their fossil ancestors also preferred to 

 dwell in moderately deep water. The fossil Lithistidae, espe- 

 cially in the Upper Jura, and here and there also in the Upper 

 (Cretaceous, are very frequently accompanied by numerous 

 Hexactinellida? ; but there are localities (e. g. the Chalk of 

 Touraine, Normandy, and Yorkshire) where the Lithistida^ 



