16 WI SCO A. JIN PHYTOPLANKTON 



Cells 355 ju, long ; 24 /x broad at semicell base, 16.5 /x at apex ; isthmus 

 22 fi broad. 



Speese (rrr). 



The dimensions of the variety as found in Wisconsin lakes agree 

 very closely with those that W. & G. S. West give for their Ceylon 

 specimens. 



var. ELONGATUM W. Wcst. PI. 54, Fig. 10. 

 Jour. Linn. Soc. Bot. 29: 119. 1892; W. & G. S. West, Monogr. Brit. Desm. 1: 

 207, pi. 30, fig. 3. 1904. 



Length about 25 times the breadth; cells somewhat narrower than 

 the type. (Tychoplanktont.) 



Cells 560 /u, long; 24 fi broad at base of semieells, 17 ju, at apex; 

 isthmus 20 ju, broad. 



Jenny (rrr). 



4. Pleurotaenium truncatum (De Brebisson) Nageli. PI. 55, 



Figs. 1-2. 



Gatt. einz. Algen 104. 1849; W. & G. S. West, Monogr. Brit. Desm. 1: 203, 

 pi. 29, figs. 3-4. 1904. 



Cells large, length about 8 times the greatest breadth, median con- 

 triction well defined; semieells cylindrical in lower half and then 

 attenuated to a truncate apex that is about half the breadth of the 

 base of the semieells, semicell bases with a single, distinct, basal in- 

 flation ; lateral margins convex, apex slightly tumid and with rounded 

 lateral angles; apical tubercules small flattened elevations, about 

 seven visible in front view of cell. Chloroplasts numerous, about eight 

 visible in front view of cells ; parietal, slightly undulate, longitudinal 

 bands with numerous pyrenoids. (Tychoplanktont.) 



Zygospores unknown. 



Cells 535-577 /ii long ; 70-72.5 fi broad at base of semieells, 32.5-77 ft 

 at apex ; isthmus 60-64 fi broad. 



Carroll (rrr), Dutchmans (rrr). 



In one specimen the lateral margins possessed two undulations 

 above the swollen bases of the semieells. Unfortunately no other 

 cells were collected from this station so that it is impossible to state 

 whether or not this undulation in the lower part of the semicell is a 

 constant feature. 



5. Pleurotaenium nodosum (Bailey) Lundell. PI. 54, Fig. 11. 



Nova Acta Eeg. Soc. Sei. Upsaliae 3 Ser., 8: 90. 1871; W. & G. S. West, Monogr. 

 Brit. Desm. 1: 214, pi. 31, figs. 3-6. 1904. 



Cells large, length about 8 times the breadth, median constriction 

 conspicuous; semieells cylindrical, with lateral margins convergent 

 towards a truncate apex and with four tumors on each margin ; with 

 four transverse whorls of mamillate tumors, one whorl at semicell 

 base and the other three equidistant between basal whorl and apex; 



