CUSHMAN: DESMIDS FROM COLORADO 163 
XANTHIDIUM HASTIFERUM JouNsont W. &. G. S. West, Jour. 
Linn. Soc. Bot. 33: 299. pl. 17. f.17. 1898; forma longis- 
pinum form. nov. (PLATE 7, FIGURE 8.) 
Spines much longer and stouter than in the typical variety as 
figured by Johnson (Bull. Torrey Club, 22: 295. p/. 293. 
J. To. 1895). Often with several additional granules below 
the usual row. Long. s. spin. 56/4; long. c. spin. 874; 
lat. s. spin. 50; lat. c. spin. 96y; lat. isthm. 144. 
(H. C. no. 454.) Common. 
Xanthidium hastiferum Toweri var. nov. (PLATE 7, FIGURE 9.) 
Long. s. spin. 57 #; long. c. spin. 714; lat. s. spin. 46.5 4; 
lat. c. spin. 102; long. spin. 234; lat. isthm. 12p; 
crass. 344. Variety with longer spines than usual, the 
apical spines usually entirely wanting. Membrane smooth 
and without thickenings. Close to var. ¢evolutum as. 
figured by Nordstedt (Sv. Vet.-Acad. Handl. 22°: pl. 4. 
J: 24. 1888), but the spines are longer and stouter and 
the membrane is not thickened or colored in any way in 
the middle of the semicells, as in that variety. 
This tends toward certain varieties of X. antilopeum 
but specimens were found with a trace of a rudimentary 
spine in the position where it would be found in typical 
X. hastiferum. The variety is named for the collector, 
Mr. W. S. Tower. 
Micrastertas ROTATA (Grev.) Ralfs, Ann. Nat. Hist. 14: 259. pl. 
OJ. f 1844 
Long, 270; lat. 226; lat. lob. pol. 60y; lat. isthm. 55 /. 
Close to the form figured by Wolle, Desm. U. S. ed. 2. p/. 
38.7.2. (H.C. no, 422.) 
STAURASTRUM ECHINATUM Bréb. in Ralfs, Brit. Desm. 215. p/. 35. 
ae 1648: 
Lat. 31 yp, (H. C. no. 422.) 
Staurastrum Johnsoni Coloradense var. nov. (PLATE 7, FIG- 
URE IO.) 
Differs from the species (S. Johnsont W. & G. S. West, Trans. 
Linn. Soc. Bot. II. 5: 266. pl. 17. f. 16. 1896), in being 
