260 
\V. E. WADE 
C. wiltrockii var. qiiasidepressum Skuja. Marquette and Meno- 
minee Counties. 
Arthrodesmus Ehrenb. 
Arihrodesmiis controversus var. brasiliense Borge. Specimens from 
Schoolcraft County resemble this variety except for a slight 
retuseness in the médian portion of the apex. 
A. crassus West and West fa. Berrien County. 
A. impur (Jacobs) Grônbl. Chippewa and Roscommon Counties. 
The only other reports of this species in North America are 
those of Taylor (1934) for New Foundiand and Prescott 
(1935) for Massachusetts. 
A. inciis fa. semilunaris Schmidle. Chippewa County. 
A. incns var. longspina Eichl. and Racib. Ingham County. 
A. Ralfsii var. Brebissonii (Racib.) Smith. Presque Isle County. 
A. ienuissimus Archer. Houghton County. 
A. iriangularU Lagerheim. Calhoun County. 
A. frispinatus West and West. Specimens from Barry County 
agréé with those shown by Skuja (1928) which do not show three 
spines supcrimposed at each angle in vertical view as in the 
typical. 
Spinocosmarium Prescott and Scott. 
Spinocosmarium giiadrideiis (Wood) Prescott and Scott. Emmet 
County. 
Xanthidium Ehrenb. 
Xanthidium antilopaenm fa. michiganensis fa. nov. (PI. 2, Fig. 1). 
Semicellula hexagonalis par spinarum longarum divergenthim 
uiroque in angulo apicali lateralique, necnon spinam unam bre- 
oiorem convergentem uiroque in angulo basali habens; regione 
centrali membranae semicellulae ordine scrobiculationum in 
tribus circuli quadraniibus dispositaruni praedita. Cellula 50 \l 
long, cum spinus 70 ij. long., i2 |x lai., cum spinis 65 ij. lat. Isth- 
mus 10.5 y. làt. 
Semicell hexagonal with a pair of long divergent spines at 
each apical and latéral angle, a single shorter convergent spine 
at each basal angle, central area of the semicell wall with a 
three-quarter circuler row of scrobiculations. Cell length 50 [a, 
cell length with spines 70 a, cell width 42 ja, cell width with 
spines 65 y, isthmus 10.5 y.. Robinson Lake, south of Roscom¬ 
mon, Roscommon County, Michigan. 
Soores MNHN, Pans 
