44 Clarence J. Elmore 



Order NAVICULALES 



Family 3. TABELLARIACEAE 



Rachis a narrow unmarked strip, no raphe, cells usually little 

 shorter than broad, or longer, mostly in filaments ; valves sym- 

 metrical, long-elliptic, often swollen in the middle, never cuneate 

 at the ends ; with two or more septa ; girdle face rectangular. 



7. Tetracyclus 



Tetracyclus Ralf s in Ann. and Mag. Nat. Hist., Vol. 'XII. 184J. 



Etym., Gr. rerpa, four, and k6kXo<; , circle, the valve being divided 

 into four circular portions. 



Cells tabulate, united in short bands by numerous interzones ; 

 with somewhat distant and irregular transverse ribs which in girdle 

 view appear as marginal teeth ; without nodules ; girdle view rec- 

 tangular; chromatophores granular, scattered. 



A. Cells inflated in the middle. I. T. lacustris. 



AA. Cells elliptical, without inflation. 2. T. rupcstris 



1. Tetracyclus lacustris Ralfs in Ayin. and Mag. Nat. Hist., Vol. 



XII, p. 105, pi. 2, fig. 2. 1843. 



PI. I, figs. 34-35. 



Cells in valve view elongated, much swollen in the middle, 35- 

 65 yu. long; transverse ribs 4-12, curved toward the center; stri- 

 ations very indistinct, 25-30 in 10 /x; the girdle side with alternate 

 short ribs ; cells in long filaments showing numerous septa. 



In moss at Snake Creek Falls, Valentine. 

 Fossil : Greeley Co., Williams's Canyon. 



2. Tetracyclus rupestris (A. Br.) Grun. Ocst. Diat., p. 412, pi. 



7. fig- 37- 1S82. 

 Gornphogramma rupcstre A. Br. in Rahcnh. Si'issw. Diat,, p. 33, 

 pi. p, fig. I. 1853. 



PI. T, fig. 36. 



Cells in valve view elliptic-lanceolate. 8-25 /x long, usually with 

 2-5 heavy transverse ribs; striations very delicate, about 18 in 

 lOju,; cells single or two or three united, in girdle view usually 



