STAURASTRUM. 141 



ST. PUNCTULATUM, Breb. Plate LIT, figs. 43-45. 



Cytiodenn punctate granulate, semi-cells elliptic, straight, 

 ends broadly rounded; end view triangular, angles not pro- 

 duced, broadly rounded, sides lightly retuse. 



Diameter 30-35 /<. 



Frequent in marsh pools, ditches, on dripping rocks and the 

 like. 



ST. PYGM^UM, Breb. Plate LIII, figs. 14-21. 



Small, sinus wide, subrectangular ; semi-cells cuneiform or 

 broadly elliptic, often alternately attached, angles more or 

 less obtuse, and sometimes spinous; membrane granularly 

 rough. 

 Diameter 16-25 n. 



Variable in size and form. They may be separated into 

 three divisions. 



Forma, GENUINA, Breb., figs. 14, 15. 

 Forma, TRUNCATA, Wolle, figs. 16-19. 



Forma, RHOMBOIDES, Wolle, figs. 20, 21. 



Found in nearly all standing or quiet waters, sometimes in 

 large numbers. 



ST. MEGALONOTUM, Nord., var. OBTUSUM, Hast. Plate XLII, 



figs. 6, 7. 



Small, about one-fourth longer than broad; cytioderm 

 granulate; isthmus about one-half width of cell ; sinuses 

 acute angled, opening outwardly; semi-cells truncately coni- 

 cal, base convex, sides concave, the truncate end with six 

 conical processes, only four of which are usually visible in 

 side view, basal angles obtuse (differing in this respect from 

 Arctic varieties) ; transverse view triangular, the angles 

 rounded, the sides slightly concave. 

 Diameter 45 i^. 



Ponds and brooks, Rochester, New Hampshire. 



ST. MINNEAPOLIENSE, Wolle. Plate XLVIII, figs. 11-13. 



Small verrucose ; semi -cells in front view subcuneate with 

 the two opposite superior angles drawn out into a short arm 

 with margins serrate, and apices finely toothed; arms di- 

 verging from the arms of the connected semi-cell ; in vertical 

 view arms straight, body much elevated on each side; in 

 lateral view arms straight, short ; body puffed out high on 

 each side, crenate on the apices. 



