63. Valves with costae forming the transverse markings; costae 



punctate Brebissonia 



PL 7, Fig. 18 



63. Valves with ornamentation formed by puncta, or without evident 

 markings 64 



64. Lateral valve markings strongly oblique, interrupted in the midregion 

 by an undecorated area over the central nodule which extends to 



the margins of the valves Stauroneis 



PI. 6, Fig. 16 



64. Central undecorated clear area not extending to the margins of 



the valve 65 



65. Transverse ornamentations composed of costae, the axial field us- 

 ually broad Pinnularia 



PI. 7, Fig. 12 

 65. Transverse ornamentations composed of puncta, the axial field nar- 

 row and linear Navicula 



PI. 7, Fig. 10 



A 



i 

 J 



[949] 



