122 



Clarence J. Ehnore 



14. Cymbella helvetica Kiitz. Bacill., p. yg, pi. 6, fig. 13. 1844. 



PI. 16, fig. 621. 



Lanceolate with dorsal margin convex, ventral margin slightly 

 concave but swollen in the middle, 36-88 ;u. long, 10-15 /a wide; 

 raphe nearly straight but slightly curved, the ends at the central 

 nodule bent toward the ventral margin ; raphe surrounded by a 

 narrow hyaline space which at the center is widened to about one- 

 third the width of the valve; terminal nodules elongated; striations 

 distinct, 8-9 in 10 fi. 



In White River, Andrews. 

 Fossil : Agate. 



31. Encyonema 

 Encyonema Kiitz. Syn. Dial., p. 61. 1834. 



Etym., from Gr. lyKvo?, pregnant, and vrifxa, thread, the cells 

 being connected by a gelatinous mass into threads. 



Cells usually enclosed in gelatinous tubes ; like Cymbella in out- 

 line ; raphe straight ; terminal nodules somewhat distant from the 

 ends. Chromatophores and auxospores as in Cymbella. 



A. Terminal nodules distant from the ends of the valves. 



I. E. prostratiiiii. 

 AA. Terminal nodules nearer the ends of the valves. 



h. Striations coarsely granular. 2. E. tnrgidnm. 



bb. Striations finely granular. 3. E. veiitricosu>n. 



I. Encyonema prostratum (Berk.) Kittz. Bacill., p. 82, pi. 25, 

 fig. 7. 1844. 



Moncma prostratum Berk. Brit. Alg., pi. 4, fig. j. 1833. 



PI. 17, figs. 622-624. 



Roughly lunate, 40-100 /a long, 19-30^ wide, dorsal margin very 

 convex, ventral margin nearly straight, more or less gibbous; 

 apices blunt, usually bent toward the ventral side ; raphe straight, 

 not reaching to the ends of the valve; striations radiate, often con- 

 verging or parallel at the ends, 7-10 in 10 jx, extending nearly to 

 the raphe, those in the middle of unequal length, leaving a wider 

 space. Fig. 624 is drawn from specimen in Rabcnh. Alg. En., 

 1208. 



In springs, creeks, rivers, etc., usually with Spiroyyra or similar algae : 



