— 167 — 
In general appearance and curvature this form resembles Cl. littorale 
Gay var. crassum West & G.S. West, but it is readily distinguished by 
its much smaller size and its truncate apices. 
b. Forma polis paullo crassioribus. (Tab. nostr. Il, fig. 3). 
Long. 100; lat. 14,542; lat. apic. 5,5 ye. 
On rocks in riverbed. 
Area: Europe, N. America, Samoa. 
40. (. gracile Bréb. 1839, in Mém. Soc. Sciences, Cherbourg, 1856, 
IV, p. 155, t. Il, f.45. C. émneticum Lemmermann in Pléner Forschungs- 
berichten, Teil 7, 1899, p. 28, t. II, f. 39—41. 
Long. 269 p; lat. 6,5 p. 
In muddy ricefields. 
Area: Europe, N. and S. America, E. Africa, Sumatra, New Zealand and 
Australia. 
41. €, acutum Bréb. in Ralfs Brit. Desm. p. 177, t. XXX, f. 5a@et d. 
Long. 138—144 yp; lat. 5,3—7 pw. 
In muddy ricefields. 
Area: Europe, N. America, E. Africa, India, Burmah, Sumatra, Central 
China. New Zealand and Australia. 
Pleurotenium Nag. 
42. P. Trabecula Nag. Gatt. einzell. Alg. 1849, p. 104, t. VI, f. A. 
Closterium Trabecula Ehrenb. 1830. i 
Long. 462—564 yw; lat. ad bas. semicell. 28--30,5 2; lat. ad apic. 
semicell. 20—20,5 x. 
In stagnant water in riverbed. 
Area: Europe, N. and S. America, Siberia, India, E. Indies, Sandwich Is., 
China, Japan, Abyssinia. 
43. P. maximum Lund. in Acta R. Soc. Scient. Upsala, ser. 3, VIII, 
1871, p.89. Docidium maximum Reinsch in Abhandl. Naturhist. Gesellsch. 
zu Niirnberg, III, 1866, p. 1884, t. XII, f. 4. Plewroteenium Archerii Delp. 
in Memor. Accad. Sci. Torino, ser.2, XXX, 1877, p. 118, t. XIX, fig. 12-16. 
Long. 522—560 p; lat. ad bas. semicell. 38—41,5 4; lat. ad med. 
semicell. 31—33 y; lat. ad apic. semicell. 22—24 yp. 
In stagnant water among other Desmids. 
Area: Europe, N. America, Abyssinia, W. Africa, Ceylon, Central China. 
44, P. gloriosum West & G.S. West. Docidium gloriosum Turn. in 
Kungl. Sv. Vet. Akad. Hand]. Bd. 25, no. 5, 1893, p. 30, t. Il, f. 5. 
Forma paullo minor, inflatione parva singula ad basin semicellularum. 
