The Diatoms of Nebraska 103 



25. Brebissonia {V anheurckia, Frustulia) 



Brebissonia Griin. in IVicn. Verh., p. ^12. i860. 



VanJieurckia Breb. Ess. Monog. sur le Vanheurckia. 1868. 



Fntsfidia Grun. Dcsm. Diat. Ins. Banka, p. 10. 186 j. 



(Not Frusfulia Ag. Syst. Alg., p. XIII ^ i, 1824.) 



Etym., named for Brebisson. 



Cells like Navicula, free or very rarely enclosed in gelatinous 

 tubes; striations fine, parallel or slightly radiate in the middle of 

 the valve ; raphe enclosed between two siliceous ribs ; terminal and 

 central nodules more or less elongated. Striations composed of 

 dots arranged in transverse and longitudinal rows. Chromato- 

 phores two plates lying next to the girdle, not changing their posi- 

 tion in the cell before division. Auxospore formation ; two cells 

 arrange themselves parallel to each other in a mucous mass and 

 form after casting off their shells two cylindrical, transversely 

 striated auxospores which lie parallel to the old valves, the ends of 

 the auxospores forming caps which are later thrown off ; valves of 

 the daughter cells formed within the perizonium. 



d. Elliptic-lanceolate, central striations radiate. I. B. vulgaris. 



AA. Linear-lanceo!ate, all striations perpendicular 2. B. intcrposita. 



I, Brebissonia vulgaris (Thwait.) Kuntze. Reif. Gen. Plant., 

 Ill, 2, p. 3p8. 1900. 



Collectoncma zndgare Thwait. in Ann. Nat. Hist., ser. 2, Vol. I, 

 pi. 12. 



Vanheurckia vulgaris (Thwait.) V. H. Diat., p. 240. i8p6. 



PI. 13, fig. 509. 



Elliptical-lanceolate, 44-70 /x long, 11-15^ wide, apices obtuse, 

 slightly attenuate, central nodule elongated ; striations fine, more 

 distant in the center, 24-34 in 10 ja, slightly radiate in the center, 

 nearly perpendicular to the raphe at the ends; cells enclosed in 

 unbranched gelatinous tubes. 



In springs, creeks, etc., and on muddy ground : Brock, Dewey Lake, 

 Grand Island, Julian, Lincoln, Mason City, Peru, Seward, Talmage, Teka- 

 mah. 



Blackhand, Rodney, Ohio. 



