THE GREEN ALGAE OF NORTH AMERICA 103 



4. Spore with pitted median membrane. Sect. SCROBICULATA. 7., 



5. Spore bluish. 4 . Z. chalybeospermum. 



5. Spore brownish. 6. 



6. Vegetative filaments 20-22 /j. diam. 5. Z. leiospermum. 



6. Vegetative filaments 26-30 M diam. 6. Z. insigne. 



7. Spores uniformly globose. 7. Z. cruciatum. 



7. Spores usually oblong. 8. /.. stellinum. 



1. Z. PECTINATUM (Vauch. ) Agardh, 1817, p. 102; De 

 Bary, 1858, p. 77, PI. I, figs. 15-19; PL VIII, Fig. 13; Zygo- 

 ooninm pectinatum Wolle, 1887, p. 225, PI. CXLV, figs, i and 

 2; P. B.-A., No. 1216. Vegetative cells 30-37 p diara., 1-3 

 diatn. long ; membrane at first thin, later with a thick, gelati- 

 nous sheath ; conjugation scalariform ; spores globose or broadly 

 ellipsoid, about 50 p. diam.; membrane brown, distinctly pitted. 

 Mass., N. J. Europe, So. America. 



Var. ANOMALUM (Ralfs) Kirchner, 1878, p. 126; Z. anoma- 

 lum var. crassum Wolle, 1887, p. 224, PI. CXL,IV, figs. 9-13. 

 Cells 40-50 /u, diara.; membrane very thick. Vermont, Mass., 

 Conn. Europe. 



Var. DECUSSATUM (Vauch.) Kirchner, 1878, p. 127; P. 

 B.-A., 1415. Zygogonium decussatum Wolle, 1887, p. 226, PI. 

 CXLV, figs. 4 and 5. Cells 18-20 p. diam., membrane not con- 

 spicuously gelatinous. Mass.; "Ponds, stagnant and sluggish 

 water." Wolle. Europe. 



Forma TERRESTRE (Rab.) Kirchner, 1878, p. 127; P. B.-A., 

 No. 1365. Membrane thick, dark-colored, cell shorter than in 

 the type ; on ground along the edges of ponds. Mass. Europe. 



2. Z. PACHYDERMUM W. and G. S. West, 1895, P- 26( >, PI. 

 XII, figs. 1-16. Filaments flexuous, somewhat geniculate ; 

 vegetative cells 16-23 M, usually 20 p diam., 2-3 diam. long; 

 membrane up to 5 /u. thick ; short, irregular,' rhizoidal branches 

 of 2-6 cells frequent ; conjugation scalariform ; spores globose, 

 subglobose, ellipsoid or of irregular shape, 25-35X19-26 /u.; 

 membrane up to 6 yu. thick, lamellate ; aplanospores similar but 

 somewhat smaller and with thinner membrane. In warm muddy 

 water. Dominica. 



Var. CONFERVOIDES W. and G. S. West, 1895, p. 266, PI. 

 XIV, figs. 1-6. Cells 10-13 /A diam., l ~ 2 diam. long; reproduc- 

 tion unknown. With the type. 



The irregularly formed spores with thick, lamellate walls may 

 be a result of the peculiar thermal conditions under which this 

 species occurs ; but it can hardly be considered as a form of any 

 other of our species. 



