334 Wisconsin Academy of Sciences, Arts, and Letters . 
corners broadly rounded. In the emargination of the sides and 
in the rounded cell angles it resembles T. trilobatum, but I feel 
that it should not be considered a variety of this species since 
T. trilobatum is always triangular. 
Tetraedron regulare Ktz. 
Pine (rrr). 
var. torsum (Turner) Brunnth. 
Black (1) (rrr), Burned Rock (r), Butterfly (r), Cornell (rr), Harbon 
(sss), Loon (rrr), Pennsylvania (rrr), Silver (1) (rrr). 
Tetraedron victorieae var. major G. M. Smith 
Butterfly (rrr). Black (1) (rrr). 
Tetraedron caudatum (Corda) Hansg. 
Burned Rock (rrr), Clear (2) (rrr). 
Tetraedron gracile (Reinsch) Hansg. PI. VIII, figs. 12-13. 
Butterfly (r), Gull (1) (rrr), Harbon (rrr), Pine (rrr). 
The branching of the processes in certain of the cells collected 
from Harbon and Butterfly lakes was greatly reduced, but this 
reduction in the branching does not seem sufficiently constant to 
warrant varietal recognition. 
Tetraedron limneticum Borge. 
Butterfly (rr), Clear (1) (rrr), Harbon (rr), Long (1) (rrr). 
Tetraedron spiniferum sp. nov. PL VIII, figs. 9-11. 
Cells of medium size, tetragonal or pentagonal, flattened or py¬ 
ramidal. Processes at angles slightly attenuated, once or twice 
branched. Each process ending in two or three (generally two) 
long, slender, divergent spines that are either straight, slightly 
incurved or recurved. 
Diameter of cells 45-52 /x; length of spines 7.5-11 p. 
Burned Rock (r). 
The cell shape and branching of the processes is quite similar 
to that of T. limneticum , but the terminal spines are quite differ¬ 
ent. These spines are true spines and not similar to the setae 
found in Polyedriopsis . 
