Smith—Phytoplankton of the Muskoka Region. 
357 
(r) , Marion (ss), Muldrew (rr), Nine Mile (rrr), Pennsylvania (r), 
Round (2) (rrr), Round (1) (r), Rowley (rr), Strange (sss), Thompson 
(sss). 
In 1882 Wolle described the varieties tetracerum and penta- 
cerum of S. Ophiura. These have, as their name implies, four- 
and five-radiate semicells which are shaped somewhat like the 
semicells of S. Ophiura. In a vertical view of S. Ophiura there 
is a coronet of quadrifid papillae with one papilla between each 
two adjacent rays of the semicell. The arms have bifid projec¬ 
tions at the base while the terminal portion is serrate and with 
a simple projection. The organism which I believe identical with 
Wolle’s S. ophiura var. pentacerum has an emarginate verruca 
between each two adjacent rays while the sides of the rays are 
denticulate and at times with a row of denticulations on the top. 
I have observed five-rayed specimens of S. Ophiura from New 
York, and in these individuals there is the typical marking of the 
seven- and eight-rayed individuals. I think, therefore, that 
Wolle’s plant cannot be considered a variety of S. Ophiura but 
must be regarded as a distinct species. The number of rays is 
generally five, but may be six. The four-rayed specimens have 
the same marking and are discussed below in connection with the 
variety tetracerum. The specific name pentacerum has been chosen 
because the name tetracerum has already been used in another 
connection. 
forma obesum forma nova. PI. XIII, figs. 1, 2. 
Body of semicells stouter and apex more elevated. 
Length 38^2 y; breadth (without processes) 25-27.5 y, (with 
processes) 105-117 y; breadth isthmus 14 y. 
Long (2) (rr), Rowley (c). 
var. tetracerum (Wolle) comb. nov. PI. XIII, figs. 3-5. 
Staurastrum Ophiura var. tetracerum Wolle. Bull, Torrey Bot. Club 9: 
28. PI. IS, fig. Jf. 1882; Desmids of the United States 134. PI. M, figs. 1, 2. 
1884. W. & G. S. West, Trans. Linn. Soc. 2 Ser. Bot. 5: 269. PI. 18, fig. 
16. 1896. 
Length 35-38 y; breadth (without processes) 15-18 y , (with 
processes) 85-115 y; breadth isthmus 10-11.5 y. 
Basil (r), Big Dudley (sss), Black (1) (sss), Brush (rrr), Butterfly 
(s) , Burned Rock (r), Clear (1) (rrr), Clear (2) (rr), Gull (1) (rr), 
Gull (2) (r), Hamer (ss), Long (1) (ss), Long (2) (s), Loon (r), 
