VI. Pyrgocystis. 



1915 5 



VI. Pyrgocystis n.g. 

 [Part I.] 



[Geol. Mag., n.s., Dec. VI, Vol. II, pp. 5-12, Pis. II, III: Jan., 1915.] 



MATERIALS for the study of this very distinctive genus have 

 been accumulating for many years, and at last afford a firm 

 basis for certain definite conclusions. Some important matters remain 

 obscure, and the comparison of the Swedish material has been 

 hindered by the dangerous state of the North Sea, but further delay 



