98 WISCONSIN PHYTOPLANKTON 



tical plane, processes generally smooth in outline, sometimes witli 

 2-3 transverse rings of coarse conical granules in the basal portion; 

 median portion of base of processes with an axial or a double row 

 of granules; body of semicells with two emarginate verrucae just 

 within each lateral margin. Vertical view of chloroplast with a 

 small central mass and two long arcuate lobes running to the base of 

 each process; pyrenoid single and central. (Euplanktont.) 



Zygospores unknown. 



Cells 70-86 /* long with processes, 25-34 ju, long without processes ; 

 breadth with processes 77-105 jx, without processes 17-20 /a ; breadth 

 at isthmus 8-9 /x; length of terminal spines 9-11 ju. 



Bear (rrr), Devils (rrr), Dummy (r). 



A very distinctive species in which the long straight divergent 

 processes termining in two divergent spines are quite unlike those 

 of other plankton species of the genus. The ornamentation of the 

 body of the cell and the base of the processes is somewhat variable. 

 In some cases the bases of the processes have three or four rings of 

 conical granules, in others the granules are found only on the upper 

 and lower sides, while in still others the granules are lacking. The 

 emarginate verrucae at the apex of the cell are at times absent. This 

 lack of an ornamentation of the body of the cell is not always cor- 

 related with a lack of ornamentation of the processes since specimens 

 with the best development of ornamentation of processes may have a 

 lack of body ornamentation or vice versa. 



35. Staurastrum contortum sp. nov. PL 76, Figs. 17-20. 



Cells of medium size, breadth (with processes) generally about 

 twice the length, deeply constricted, sinus obtuse-angled and widely 

 open, isthmus narrow; semicells broadly obtriangular, with ventral 

 and dorsal margins straight ; body of semicells small and not 

 sharply diif erentiated from the long attenuated processes ; processes 

 divergent, with margins sharply crenulate and ends tridenticulate. 

 Semicells almost invariably twisted, usually at right angles to each 

 other. Vertical view narrowly elliptic, with the poles prolonged 

 into straight processes with undulate sides and trispinate ends; 

 processes of the two semicells generally cruciform. Chloroplast, 

 laminate, with one pyrenoid. 



Zygospores unknown. 



Cells 36-67 /M long with processes, 12 /;, long without processes; 

 breadth with processes 44-119 p., without processes 10.5-12 /a; breadth 

 at isthmus 6 p, ; thickness 6 ju,. 



Big Bass (rrr), Bone (ss). Found (rrr). Grindstone (rr). 



Twisting of the semicells is well known in some of the other small 

 biradiate species of the genus but semicells lying at right angles to 

 each other are quite unusual in the other species. This species shows 



