WISCONSIN PHYTOPLANKTON 75 



triangular, with ventral margins slightly convex and dorsal margins 

 convex to slightly concave ; lateral angles acute and furnished with 

 a single, medium-sized, acutely pointed, straight spine ; spines usually 

 subparallel, though at times somewhat convergent or divergent. Ver- 

 tical view triangular (very rarely quadrangular), with sides of cells 

 retuse in the median portion; angles acute, furnished with a simple 

 straight spine. Cell wall smooth. Chloroplast triangular in outline, 

 fairly massive, with two parallel laminate lobes running to each angle 

 of the semicell; pyrenoid single and central. (Facultative plank- 

 tont.) 



Zygospores spherical, with several mamillate projections, each ter- 

 minating in a short stout spine (Ralfs). 



Cells 23-28 fj. long ; breadth with spines 42-53 fi, without spines 

 19-26 ju,; breadth isthmus S/x; length of spines 15-20 /x. 



Diameter of zygospores 30 ju, (Ralfs). 



Beaverdam (rrr), Big Bass (rr), Bird (rrr), Chain (sss), Clare (rrr), 

 Crawling Stone (rr), Devils (rr), Duck (rr), Dutchmans (rrr). Grindstone (rrr), 

 Half Moon (rrr), Horseshoe (r), Jag (rrr), Lac Court Oreilles (rrr), Lac du 

 Flambeau (rrr), Little Bass (rrr). Little Doctor (rrr), Lost (rr), Big McKenzie 

 (rr), Mercer (rrr), Mud (rr), Muskallonge (rr), Nicaboyne (rrr), Owen (ss), 

 Sishebogema (rr). Tank (sss), Travis (rrr), Whitefish (sss), "Wolf (rrr). 



The species can be distinguished at once from other triradiate 

 species with a single spine at each angle of the semicells by the smaller 

 size and the elongate isthmus. 



var. CANADENSE G. M. Smith. PI. 69, Figs. 1-3. 



Trans. Wis. Acad. Sci. Arts & Letts. 20: 349, pL 10, figs. 23-24. 1922. 



Cells with a distinct indentation at the point of union of the two 

 semicells; spines usually divergent. (Euplanktont.) 



Cells 37-39 /a long with spines, 26-32 fx long without spines ; breadth 

 53-58 fji with spines, 21-23 ju, without spines ; isthmus 5 ix broad ; spines 

 18-22 fi long. 



Clear Crooked (rr). 



14. Staurastrum megacanthum Lundell. PI. 69, Figs. 16-21. 

 Nova Acta Eeg. Soe. Sci. Upsaliae 3 Ser. 8: 61, pi. 4, fig. 1. 1871. 



Cells of medium size, about as long as broad (without spines), 

 deeply constricted, sinus acute-angled to subrectangular, with an 

 acute apex ; semicells obversely triangular, with apex generally tumid, 

 rarely straight; lateral margins of cells straight to slightly convex, 

 angles with a single stout straight elongate spine ; spines usually sub- 

 parallel, rarely subdivergent. Cell wall smooth to finely punctate. 

 Vertical view triangular, with sides somewhat retuse in the central 

 portion, angles acute and with a single stout straight spine. (Faculta- 

 tive planktont.) 



Zygospores unknown. 



Cells 36-46 long with spines, 36-40 /x long without spines ; breadth 

 with spines 58-72 ju, without spines 41-49 /x ; breadth of isthmus 

 10-11.5 /x; spines 12.5-17 )n long. 



