— 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. II, fig. 3). 

 Long. 100 fi; lat. 14,5/i; lat. apic. 5,5 ju. 



On rocks in riverbed. 



Area: Europe, N.America, Samoa. 



40. C. gracile Bréb. 1839, in Mém. Soc. Sciences, Cherbourg, 1856, 

 IV, p. 155, t. II, f. 45. C. limneticum Lemmermann in Plöner Forschungs- 

 berichten, Teil 7, 1899, p. 28, t. II, f. 39-41. 



Long. 269^; lat. 6,5^. 

 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. 5 a ei b. 

 Long. 138 — 144 lat. 5,3 — 7/^. 



In muddy ricefields. 



Area: Europe, N. America, E. Africa, India, Burmah, Sumatra, Central 

 China. New Zealand and Australia. 



Pleurotænium Näg. 



42. P. Trabecula Näg. Gatt, einzell. Alg. 1849, p. 104, t. VI, f. A. 

 Closterium Trabecula Ehrenb. 1830. 



Long. 462 — 564 ^; lat. ad bas. semicell. 28 — 30,5 u; lat. ad apic. 

 semicell. 20— 20,5 p. 



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, VIU, 

 1871, p. 89. Docidium maximum Reinsen in Abhandl. Naturhist. Gesellsch. 

 zu Nürnberg, III, 1866, p. 1884, t. XII, f. 4. Pleurotænium Archer ii Deip. 

 in Memor. Accad. Sei. Torino, ser.2, XXX, 1877, p. 118, t. XIX, fig. 12-16. 



Long. 522 — 560 /./; lat. ad bas. semicell. 38 — 41,5 fi) lat. ad med. 

 semicell. 31—33 p; lat. ad apic. semicell. 22—24 



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. Handl. Bd. 25, no. 5, 1893, p. 30, t. Ill, f. 5. 



Forma paullo minor, inflatione parva singula ad basin semicellularum. 



