Smith—Phytoplankton of the Muskoka Region. 
347 
on the apex of the semicells. The dimensions of the individuals 
that I have found are smaller than those found by Cushman. 
Xanadithium antilopaeum (Breb.) Ktz. 
Leech (rrr). 
var. limneticuxn var. nov. PI. X, figs. 14-16. 
Semicells with spines on lower angles gracefully curved and 
those on upper angles straight and divergent. Central area color¬ 
less or brownish, generally with an arc of 4-8 subapical pores, 
more rarely with an irregular ring of pores. 
Length (without spines) 51-56 y, (with spines) 81-90 y; 
breadth (without spines) 47-50 y, (with spines) 87-100 y; 
breadth isthmus 12-14 y. 
Gull (1) (ss). Hamer (rrr), Muskoka (rrr), Pennsylvania (r), Sil¬ 
ver (1) (s). 
The elegant curvature and length of the spines in this variety 
distinguish it from the typical X. antilopaeum. The ornamenta¬ 
tion below the apex suggests the variety polymazum, but in this 
variety the marking is due to pores while in the variety polymazum 
the marking is due to small rounded granules. 
var. polymazum Nords. 
Black (1) (rrr), Burned Rock (rrr), Gull (1) (rr), Joseph (rrr). 
Little Dudley (rrr), Long (2) (rrr), Marion (rrr), Otter (rrr), Penn¬ 
sylvania (rrr), Round (2) (rrr), Rowley (rrr), Silver (1) (rrr), White 
(rrr). 
var. minneapoliensis Wolle 
White (rrr). 
ARTHRODESMUS Ehrenberg 1836 
Arthrodesmus incus (Breb.) Hass. 
Otter (rrr). 
var. ralfsii W. & G. S. West 
Strange (rrr). 
var. indentatus W. & G. S. West. 
Clear (1) (rrr). 
