10 LINDSTRÖM, ON THECOCYATHUS NATHORSTI. 



tbree cycles of septa and four in one system. The septa have 

 a dentate crest and detached papillee (= so called paluli), in no 

 way different from the few, twenty or less, papillse in the central 

 area, coramonly regarded as columella. ReüSS also says concerning 

 Thec. velatus: »Kronblättchen (= paluli) können leicht mit den 

 Axenpapillen (== Columella) verwechselt werden.» 



The chronological distribution of the species of this genus 

 is interesting as it can be followed from Lias to the present 

 times. It may be seen through the following list. 



Lias. 



Thecocyathus Moorei Edw.H. from the Upper Lias, England. 



Thec. mactra GOLDPüSS, also from the Toarcien or Upper 

 Lias, Calvados, France, S'witzerland; Thec. tlntinnabulum from 

 the same Stratum and localities is now regarded as identical 

 with Th. mactra. 



Jura. 



Thecoc. discus Fromentel, Bajocien, France. Moreover 

 there are three badly preserved species annotated by Fromentel 

 with some doubt, as belonging to this genus. They are from the 

 Oxfordien of France. 



Cretaeeous. 



Thecoc. Nathorsti LiNDSTR. Neocom, King Charles Land. 

 Thecoc. C7^etaceus From. Aptien, France, according to 

 KoJBY related to Thec. mactra. 



Thec. radiatus KoBY, Aptien, Switzerland. 



Tertiary. 



Thec. velatus Reuss. 



Thec. mic7^ophyllus Reuss, both from the Miocene of Bohemia. 



