356 Wisconsin Academy of Sciences, Arts, and Letters. 
This is a very distinctive species that I have found in all three 
regions of North America where I have studied the plankton. The 
long, smooth processes that terminate in a pair of spines are the 
distinctive feature of the species. There is considerable variation 
in the ornamentation, and the processes of some cells are prac¬ 
tically destitute of the small verrucae while other cells have 3-4 
rings of verrucae on the processes. The bodies of the semicells 
are usually without the simple verrucae on the sides of the cells 
but usually have the emarginate verrucae on the apex of the cells. 
The form shown in figure 15 with three spines at the ends of 
the processes in one semicell is most unusual and has been ob¬ 
served but twice. 
Staurastrum cerastes Lund. 
Burned Rock (rrr), Hamer (rrr), Pennsylvania (rrr). 
var. triradiatum var. nov. Pl. XII, figs. 16-18. 
Cells larger, front view with processes not so sharply incurved 
as in the typical form. Semicells with emarginate apical verrucae 
and a row of trifid or quadrifid verrucae across the ventral mar¬ 
gin. Vertical view triangular, with emarginate verrucae on the 
bases of and between the processes; central area containing a tri¬ 
angle of tridenticulate verrucae with three verrucae on each side. 
Length 50 p ; breadth (without processes) 27.5 p, (with 
processes) 70 p; breadth isthmus 10 p. 
Gull (1) (rr), Silver (1) (rr). 
\ 
This variety is distinguished by the laxer curving of the pro¬ 
cesses at the corners of the semicells and the consequent greater 
breadth in proportion to the length. The cells are always tri- 
radiate and the verrucae much more prominent than in the typical 
form. The alga should also be compared with S. elegantissimum 
Johnson. 
Staurastrum pentacerum (Wolle) comb. nov. PL XII, figs. 19-22. 
Staurastrum Ophiura var. pentacerum Wolle. Bull. Torrey Bot. Club 
9: 28. PI. 13, fig. 5. 1882; Desmids of the United States 134. PI. 43, fig. 
13; PI. U, fi9- 3. 1884. 
Length 28-30 p ; breadth (without processes) 17.5-22.5 p, (with 
processes) 81-100 p; breadth isthmus 7.5 p. 
Big Dudley (s), Black (2) (r), Brush (rr), Burned Rock (s), Corner 
(rrr), Harbon (rr), Henshaw (s), Leech (c), Little Dudley (s), Long (1) 
