WISCONSIN PHYTOPLANKTON 71 



8. Staurastrum avicula De Brebisson. PI. 68, Figs, 8-10. 



in Ralfs, Brit. Desm. 140, pi. 23, figs. IIA-IIB. 1848. 



Cells small, length about three quarters the breadth, deeply con- 

 stricted, sinus widely open and apex with acute angles, isthmus fairly 

 narrow ; semicells obversely triangular, with the dorsal margin some- 

 what inflated ; superior angles truncate and with two very short 

 divergent denticulate spines ; body of semicell with scattered granules 

 in the central portion of the apex and the granules in concentric 

 rings in the region of the angles. Vertical view triangular, with the 

 sides slightly retuse and the angles acute, angles terminating in two 

 short spines that lie in the same vertical plane (usually only one 

 visible). Chloroplast axial, with a small central body and two arcu- 

 ate lobes running to each angle of the cell ; pyrenoid single and cen- 

 tral. (Facultative planktont.) 



Zygospores unknown. 



Cells 31 IX long ; 37 fi broad with spines, 31 /x broad without spines ; 

 isthmus 10 fi broad ; spines 2-3 /x long. 



Bear (rrr), Duck (sss), Horseshoe (rrr), Shell (rr). 



9. Staurastrum lunatum Ralfs. 



Brit. Desm. 124, pi. 34, figs. 12A-12B, 1848; W. West, Jour. Linn. Soc. Bot. 29: 

 173. 1892. 



Cells small, breadth (without spines) slightly greater than the 

 length, deeply constricted, sinus acute-angled, isthmus fairly broad; 

 semicells obsemicircular, with apex convex; angles of semicells with 

 a single stout upwardly curved spine. Vertical view triangular, with 

 angles rounded and bearing a straight stout spine at each angle ; sides 

 of cell retuse. Cell wall punctate-granulate. 



Zygospores unknown. 



Cells 25 IX long without spines ; 36 ii broad with spines, 30 /u, broad 

 without spines; isthmus 12.5 /x broad (W. West). 



Not found in the plankton of Wisconsin lakes. 



var. planctonicum W. & G. S. West. PI. 68, Figs. 11-13. 

 Jour. Linn. Soc. Bot. 35: 546, pi. 16, figs. 11-12. 1903. 



Cells somewhat larger and broader than the type; angles of semi- 

 cells more arcuate in front view and with terminal spine much 

 smaller; cell wall finely granulate, with granules in concentric rings 

 near the angles but scattered in the central portion of the cell. Ver- 

 tical view with lateral margins very slightly retuse. (Euplanktont.) 



Cells 35 II long ; breadth with spines 45-54 ix, without spines 

 40-48 [X ; isthmus 10-12.5 n broad ; spines 2.5-4 ix long. 



Chain (rr), Clear Crooked (rr), Cranberry (rrr), Touud (rrr), Granite (r), 

 Lac Court Oreilles (r). 



The upwardly curved short spines at the angles of the semicells 

 combined with the granulate cell wall distinguish this species. The 

 variety has shorter spines and a more regular arrangement of the 

 granules. 



