346 Wisconsin Academy of Sciences, Arts, and Letters. 
Cosmarium quadrum Lundell 
Brush (rrr). 
Cosmarium ornatum Ralfs 
Black (1) (rrr). 
XANTHIDIUM Ehrenberg 1834 
Xanathidium armatum var. ceryicorne W. & G. S. West. 
Leech (rrr), Long (1; (irr). 
Xanthidium tetracentrotum var. hexagonum var. nov. Pl. X, 
figs. 6-8. 
Apex of semieells hexagonal, without spines, basal angles of 
semicells with one or two long, outwardly divergent spines. Cen¬ 
tral area of semicells smooth, slightly thickened but without orna¬ 
mentation. 
Length 35-40 /x; breadth (without spines) 37.5-40 u, (with 
spines) 65-70 g.; thickness 22 /x; breadth isthmus 10-12 /i. 
Portage (rr). 
The hexagonal upper half of the semicell is quite unlike that of 
any other known variety of this species. The variety is also char¬ 
acterized by longer spines and by a central area without ornamen¬ 
tation. 
Xanthidium subhastiferum var. Toweri (Cushman) comb. nov. 
PI. X, figs. 9-13. 
Xanthidium hastiferum var. Toweri Cushman; Bull. Torrey Bot. Club 31: 
163. PI. 7, fig. 9. 1894. 
Length (without spines) 35-38/x, (with spines) 50-60 /x; breadth 
(without spines) 35-40 /x, (with spines) 65-75 /x; breadth isthmus 
8.5-11.5 /x; length spines 12.5-22 /x. 
Echo (rrr), Loon (rrr), Strange (rr). 
This variety comes more appropriately under X. subhastiferum 
than under X. hastiferum. The spines on both the upper and the 
lower angles of the semicells are upwardly divergent in a grace¬ 
ful curve, while the spines of the typical X, subhastiferum are 
straight and much shorter. At times there is a supplementary 
pair of smaller spines, a single spine, or the rudiments of spines 
