348 Wisconsin Academy of Sciences, Arts, and Letters. 
Arthrodesmus constrictus sp. nov. PI. X, figs. 17, 18. 
Cells of medium size, breadth (without spines) slightly greater 
than the length, deeply constricted, sinus rectangular, with sides 
outwardly divergent; semicells broadly cuneate with convex sides 
and a slightly convex apex, lateral angles somewhat pointed and 
furnished with strong, straight, somewhat divergent spines. 
Isthmus cylindrical, elongate, with a slight constriction at the 
point where cell division takes place. Vertical view elliptic, each 
pole furnished with a single spine. 
Length 22.5-25 /a; breadth (without spines) 28-30 /a, (with 
spines) 58-68 /a; breadth of isthmus 4 /a; length of isthmus 5 /a; 
spines 15-19 /a long. 
Long (1) (rrr). Pine (rr). 
The semicells of this species are much broader in proportion 
to their length than those of any other species of the genus. The 
isthmus is also peculiar in that the point of origin of the new 
semicell is shown by an annular depression, whereas in other 
species the point of union of the two semicells is not discernible. 
Arthruuesmus triangularis Lag. 
Hamer (r), Harbon (rr), Vernon (rr). 
var. inflatus W. & G. S. West 
Portage (rr). 
var. subtriangularis W. & G. S. West 
Black (rr), Burned Book (rr), Gull (2) (rrr), Joseph (r), Long (2) 
(rrr), Muskoka (rr), Nelson (sss), Silver (1) (r), Thompson (r). 
Arthrodesmus quiriferus var. subparallelus var. nov. PI. X, 
figs. 19, 20. 
Sides of cells straight, not curved, and with the long spines at 
the angles only slightly divergent. 
Length (without spines) 20-22.5 /a; breadth (without spines) 
20-24 /a; breadth isthmus 6-7 /a; spines 28-31 /a long. 
Corner (rrr), Henshaw (rrr), Loon (rr), Rowley (rr). 
The dimensions of the cell in the variety are approximately the 
same as in the typical form, while the spines are somewhat shorter 
in the variety. This variety approaches biradiate forms of 
Staurastrum jaculiferum W. & G. S. West ever more than the 
