DIATOM ACE JE OF NORTH AMERICA. 



r Frustules marked with spiral or crossed bands in f. v. 

 9. I Liparogym LXXI. 



(. All others MELOSIRA LXXII. 



FAMILY XI. BIDDULPHIE^:. 



f Fi'iistnles with one neck-like process; generally ob- 

 lique; cohering irregularly, valves unlike... 



ISTHMIA LXXIII. 



. Frustules not as above 1 



f Frustules transversely costate in f. v. ; costae more 



or less capitate, resembling music notes ; valves 



1. ] transversely costate ; without spines or median 



line TERPSINOE LXXI v. 



Frustules not as above 2 



c Frustules transversely costate, or scalariform ; costae 

 (septae) showing in f. v., not capitate, valves often 



lunate, connecting zone hyaline or striate 



ANAULUS LXXV. 



- Frustules not as above 3 



f Frustules mostly hyaline, or imperfectly silicious, 

 forming a straight or curved filament; processes 



obscure, or absent ..EUCAMPIA LXXVI. 



I Frustules not as above 4 



f Processes generally straight on the outer margin in 

 f. v. ; and tipped with a spine or mucro. which is 



4. ! sometimes obscure HEMIAULUS LXXVII. 



All others BIDDULPHIA LXXVIII. 



I Angular forms TRICERATIUM. 



FAMILY XII. EUPODISCE^:. 



( Valves with plumose rays or dots about the flat rnas- 

 toid processes (or ocelli); rarely obscure; some- 

 times with a sub-quadrate central portion ; or a 

 radiant cellulation interrupted by a linear series 



terminating iu the ocelli AULISCUS LXXIX. 



Valves not as above 1 



f Valves circular or oval ; with the ocelli, or pseudo- 



openi ngs, in compartments Craspedoporus LXX x i . 



Valves discoid with a central thickening or obscure 

 nodule, and an interrupted raphe terminated by 

 minute spines or spiniform nodules somewhat 

 within the margin of the disc ; central portion of 

 the disc uaviculoid, depressed, its ends terminating 

 at the spines. Striae radiate moniliforni, extending 

 from r:iph(' to the margin of the valve. . .EAPHIDODISCUS. 

 Valves not as above 3 



