72 



of Primltia ToUi ; the part of llie valve of Primita ToUi which is 

 situated in front of the node, and the part of the valve with the 

 three bnlb-like })arts with that part of the valve of Primitia ToUi 



Fig. U. 

 Left valve of Beyrichia tubercu- 

 lata Klöden sp. X 10. 



Fig. 4. 

 Left valve of Beyrichia protu- 

 herans Boll. X 10. 



which is located behind the lateral grove. My opinion that this com- 

 parison was correct, was corroborated on comparing the valves of 

 the Ostracoda mentioned above with one oï Beyricliia protuberans Boi,l, 

 originating from an erratic boulder of Beyrichian limestone found at 

 Groningen, which lies between the two others in structure (fig. 4). 



From this then we may conclude that the edge near which the 

 two nodes are located, is to be regarded as anterior. 



Next I began to investigate if the structure of the free edges of 

 the tw^o kinds of valves was in accordance with the conclusion drawn 

 from the location of the muscle impression. 



For this purpose sections were made of the two kinds of valves 

 at right angles to the dorsal edge, somewhere about the muscle 

 impression. 1 then found that the structure of the free edges entirely 

 corroborated my conclusion. The valve which I had interpreted as 



Fig. 5. Fig. 0. 



Transverse section of the right Transverse section of the left valve 



valve of Beyrichia tuherculata Klö- of Beyrichia tuherculata Klöden sp., 



DEN sp., through the part of the muscle through the part of the muscle im- 



impression. anterior view. X 19. pression, anterior view. X 20. 



the right one (fig. 5) appeared to have sharp free edges and the 



