SOME DESMIDS OF THE UNITED STATES, 319 
Var. EXTENSUM. (PI. 18. fig. 19.) 
Var. processibus elongatis et tenuioribus, denticulis 4 vel 5 ad 
marginem unumquemque. 
Lat. 81 p. 
Hab. De Land, Florida. 
158. SraurastRUM Arcriscon, Lund. in Nov. Act. Soc. Scient. 
Ups. Ser. III. viii. no. ii. p. 70, t. 4. f. 8.—Xanthidium Arc- 
tiscon, Ehrenb. 
Hab. Bridgeport, Conn. Cold Spring Harbour, N.Y. Me- 
redith and Holderness, N.H. Burlington, Kansas, frequent in 
ponds with Azolla. Whitmore Lake, Mich. 
159. S. LEPTACANTHUM, JVordst. in Vidensk. Medd. Naturh. 
Foren. Kjóbenh. 1869, p. 229, t. 4. f. 46. 
The form of this species seen from Florida possessed nine 
radial processes and six apieal processes, thus having the same 
proportion (4: 6) of apical to basal processes as in the typical 
pant. Long. 48; lat. 68. (Pl. 18. f. 12.) 
160. S. Kircnenit, Wolle, 1882 ; Desm. U. S. p. 150, pl. 40. 
ff. 35, 36. 
Long. e. proc. 57-644; lat. c. proc. 57-07 u. (Pl. 18. figs. 
10, 11.) 
Hab. De Land, Florida (H. J. no. 599). 
161. S. XIPHIDIOPHORUM, Wolle, 1885 ; Alg. U.S. p. 44, pl. 57. 
ff. 21, 29. 
Var, BRACHYACANTHUM, West & G. S. West, in Trans. Linn. 
Soc. Ser, TI. (Bot.), v. p. 269, pl. 18. f. 7. 
Long. s. spin. 28 y, c. spin. 48 u; lat. 26 p. 
Hab, Seattle, Wash. 
. Probably the same as var. simplex, Wolle, but very different 
irom hig description and figure. 
XVIII. ARTHRODESMUS, Ehrenb. 
162, A, BIFIDUS, Bréb. in Mém. Soc. Sci. Nat. Cherbourg, iv. 
P. 135, t. 1, £. 19 p. 
Long. 11 k; lat. 9u; lat. istbm. 3 p. 
Hab. Seattle, Wash. 
t " A. CONVERGENS, Ehrenb. 1838; Ralfs, Brit. Desm. p. 118, 
20. f.3 
Hab. Ann Arbor, Mich.; “a form quite abundant with the 
