164 CuSHMAN: DESMIDS FROM COLORADO 
somewhat larger, with the lower side of the processes fully 
as rough as the upper. In this respect it is more like S. 
leptocladum Nordst., but it has the form of processes of S. 
Johnsoni, and the apices are tridentate. Long. 51 y; lat 
96; lat. isthm. to. (H.C. 20. 422.) 
Boston SOCIETY OF NATURAL HIsTorRY. 
Explanation of plate 7 
All figures & 450. 
Fic. 1. Pentium Digitus (Ehrenb.) Bréb, 
Fic, 2. P. closterioides spirogranatum var. nov. 
¥ic. 3. Cylindrocystis Americana W. & G. S. West. 
Fic. 4. Pleurotaenium Trabecula (Ehrenb.) Naeg. 
Fic. 5. Cosmarium balteum Coloradense var. nov. 
Fic. 6. uastrum verrucosum Ehrenb., var. 
Fic. 7. a, £. Didelta Ralfs, var. ; 4, end view 
a 
Xanthidium hastiferum Johnsoni W. & G. S. West, forma longispinum | 
form. nov 
= 
~ 
Q 
© 
Oe Ie eisstioreokd Tewivd Sax, no 
Fic. 10. Staurastrum JSohnsont ti ai var. nov. 
