cup-shaped in some, becoming massive and filling the cell; 1 or 

 more pyrenoids, usually 1 in each angle of the cell. 



This genus should be compared with the pyramidal species of 

 Tetraedron, in which the angles of the cell are sometimes drawn 

 out to form arms. Some species of Tetraedon have the angles bearing 

 spines, but these are relatively short, never equaling the diameter 

 of the cell, whereas in Treubaria the angles of the cell are spines, 

 which are much longer than the diameter of the cell body. 



Treubaria setigerum (Archer) G. M. Smith 1933, p. 499 

 [Tetraedron trigonum var. setigerum ( Arch. ) Lemmermann] 



PI. 51, Fig. 8 

 Cells triangular and flattened in surface view, the angles broadly 

 rounded and then produced to form a long tapering spine; chloro- 

 plast a parietal plate, covering the cell wall; cells 7-9fx in diameter; 

 spines 12-15;u, long. 



Rare; in tychoplankton. Wis. 



OOCYSTIS Naegeli in A. Braun 1855, p. 94 



Unicellular or in colonies of 2-16 individuals inclosed by the 

 persistent and much swollen mother cell wall of the previous 

 generation; several successive generations of cells sometimes in- 

 closed within old membranes; cells ovoid, ovoid-ellipsoid, or rarely 

 subcylindric, with rounded poles which may be smooth or furnished 

 with a conspicuous nodule-like thickening; chloroplasts 1 or many, 

 mostly parietal, of various shapes, ovoid discs, irregular star-shaped 

 plates, or reticular; 1 pyrenoid in each chloroplast (sometimes 

 wanting ) . 



Key to the Species 



1. Poles of cells with nodular thickening 2 



1. Poles of cells without nodular thickening; apices rounded or pointed . 9 



2. Cells with one pole thickened, the other broadly rounded; 



cells somewhat pyriform O. pijriformis 



2. Cells with nodular thickenings at both poles; 



cells oval, elliptic, or oblong 3 



3. Chloroplasts numerous, 4—25—60 4 



3. Chloroplasts fewer in number, 1—3 (rarely 4) 7 



4. Cells oblong, with lateral walls concave; 



chloroplasts 12-25 0. panduriformis 



4. Cells elliptic or oval (sometimes nearly round) 5 



5. Chloroplasts 40-60 irregularly lobed, parietal discs O. Eremosphaeria 



5. Chloroplasts fewer, disciform or oval, laminate 6 



6. Chloroplasts relatively large, 4—10; mother cell wall 



much swollen and inclosing 2-4-(8) daughter cells O. crassa 



6. Cloroplasts smaller and more numerous, 12—25; 

 mother cell wall not swollen; cells mostly solitary 

 (uncommonly as many as 8 in a famiy) O. soUtaria 



[242] 



