5^ 



PORODISCUS. 



GENUS 180. PORODISCUS GREV, 1863. 



.flse?37sg 





Fig. 269. Porodiscus elegans (girdle view) . 



Fig. 270. Porodiscus splendidus (valve view). 



Valves elliptic, circular, or rhomboidal, with cellular or coarsely- 

 punctate structure, showing at the median portion a pseudo-opening 

 in reality a depression the bottom of which is either hyaline (?) or 

 more or less finely punctate. 



I give, after Greville, the girdle face of Porodiscus elegans (fig. 269), and 

 the valve face of P. splendidus. 



From an examination of the forms in my collections, I cannot see any 

 difference between the Craspedodiscus and Porodiscus, except that in the latter 

 the depression is deeper and smaller. I therefore agree with the opinion of 

 Mr. Grunow, who ranks the Porodiscus with the genus Craspedodiscus. 



About a dozen forms have been classified as Porodiscus, all of which are 

 fossil, with the exception of P. Stolterfothii Cast. 



