59 



tudes. Leptobolus shows the usual large percentage of oriented and 

 reversed valves. 



In the next assise are layers, over which are scattered the valves of 

 Acrothele and an oval Leptobolus. The attitude of these valves is as 

 follows : 



ORIENTATION of valves on three small slabs of Assise E. 3 c. 



Fossils 

 oriented in 

 Assise E. 3 c. 



The second species here is more like a Lingulella in form than the 

 Leptobolus in the assise below, and responded correspondingly to the 

 orienting force. 



Orientation in the next assise shows similar conditions, but with 

 other species. 



ORIENTATION of valves on several small slabs from Assise E. 3 d. Orientation of 



two genera 

 in Assise E. 

 3d. 



Oriented 50%. Reversed 20%. Point S.E. 20%. Point N.W. 10%. 



Here the proportion of oriented ventral valves in Acrothyra proavia 

 is unusually low. 



