.'10 DIATOMACE^E OF NORTH AMERICA. 



Valves hyaline ; with a broad margin divided by 



simple rays ; center hyaline, or granulate, reticu- 



late, or minutely punctate ................... MASTOGONIA xc. 



I All others ....................................... ASTEROLAMPRA xci. 



FAMILY XV. COSCINODISCE.E. 

 f Disc with a circle of large marginal or intra-mar- 



ginal cellules ; and radiate, or scattered cellules or 



punctae Heterodictyon xcn. 



- Valves not as above 1 



f Disc with an interior ring of cellules separating the 

 .. center from the broad marginal rim ; cellulation 



of center, curved or spiral Briglitwellia xcirr. 



L Valves not as above 2 



j 



Disc very convex, or conical in f. v. ; with a con- 

 (. Valves not as above 



spicuous, central-pseudo-opening Porodiscus xciv. 



f Disc cellulose ; large, with a broad border of a differ - 

 q j ent structure, separated by a well-defined margin. 



CRASPEDODISCUS xcv. 



I Valves not as above 4 



f Disc hyaline ; with distinct umbilicus, and (very) 

 finely marked : with rayed or decussating lines... 

 4. -j HYALODISCUS xcvi. 



Probably often valves of PODOSIRA=MELOSIRA LXXII. 



Valves not as above 5 



f Disc cellulose ; with a narrow (somewhat dentate) 



P. rim; connecting zone cellulose 



ENDICTYA=MELOSIRA LXXII. 



I Valves not as above 6 



Disc without marginal spines, teeth, or pseudo- 

 nodule ; usually of small or medium size ; and 

 generally with an outer ring-like portion either 

 smooth or striate ; center often bull ate, smooth, or 



6 ' 



granulate ; granules equal, scattered, or rayed, or 



disc hyaline (or finely punctate), with strong linear 



straight rays CYCLOTELLA xcvn. 



Valves not as above 7 



f Frustules complex 1 ? disc circular, generally with a 

 marginal or submarginal pseudo-nodule (sometimes 

 absent); frequently with minute marginal spines 

 7. -J or teeth ; and with a single or double series of 

 radiating dots or punctate often subulate < !) blank 



spaces. ACTINOCYCLUS xc'vrn. 



Frustules not as above N 



