10 



1)1 ATOM ACE. E OF NORTH AMERICA. 



TRIBE IT. 



F It V S T 1 T L E S 



generally bacil- 

 lar in s.v. some- 

 times broadly 

 oval ; or snbor- 

 bicular very 

 rarely orbicu- 

 lar. Frustules 

 \\ ith or without 

 nodules : 



PSEUDO KAPHIDIlvE. 



f a pseudo-raphe (simple 

 line or blank space) 

 on one or both valves: 

 or 



longitudinal septa or 

 vithe in f. v., or 



valves fusiform, sigmoid, 

 beaked, or alate, or 



with numerous trans- 

 verse ribs, plicae, cos 

 tae. striae, or rows of 

 granules on one or 

 both valves, rarely 

 regularly radial ; cos 

 tae sometimes show 



always with either 



\ 



ing in f. v. 



without 



except spines 

 very rarely 

 among the 

 Surirellese, 

 or Tabella- 

 rie;e. when 

 the charac- 

 ter is al- 

 ready sut'li 

 ciently in- 

 dicated by 

 the above. 



never angular in s. v. 



hyaline, 

 unstriate, or 

 much developed in f. v. 

 // n1 ess longitudinally 

 septate. 



I 



processes, j 



teeth, 



spines, . 



awns, 



or true 

 raplie 

 on the 

 valves 



rarely 



