WISCONSIN PHYTOPLANKTON 23 



Cells 97.5 fi long, 52.5 /x broad at base of semieells, 24 fx. broad at 

 apical lobe, 17.5 fi at isthmus; apical incision 6 /a deep. 



Zygospores 73.6-86 ix in diameter without papillae ; papillae 9-13 /* 

 long (W. & G. S. West). 



Big. St. Germain (rrr), Fish (rrr), Meta (rrr). 



3. EuASTRUM OBLONGUM (Grevillc) Ralfs. PI. 56, Fig. 3. 



Ann. & Mag. of Nat. Hist. 14: 189, pi 6, figs. 4A-4C. 1844; Brit. Desm. 80, 

 pi. 12, figs. A-G. 1848. 



Cells large, length about twice the breadth, deeply constricted, 

 sinus linear, with apical portion somewhat inflated and outer margin 

 widely open, isthmus narrow; semieells subrectangular, distinctly 

 five-lobed, polar lobe broadly euneate, with apex strongly tumid, 

 angles broadly rounded and polar incision deep and narrowly 

 V-shaped ; interlobular incisions deep, open and with rounded apices ; 

 superior lateral lobes subquadrate, somewhat smaller than the inferior 

 lateral lobes and at an angle with the long axis of the semicell, 

 margins somewhat retuse; inferior lobes subquadrate, with rounded 

 angles and concave margins. Cell wall punctate and with a large 

 protuberance just above the isthmus and one just within the mar- 

 gins of both the inferior and superior lateral lobes. Vertical view 

 broadly elliptic, with poles rounded and four protuberances on each 

 side of the cell. Lateral view narrowly elongate-pyramidate, with 

 bases parallel for a short distance and then converging to a truncate 

 apex. Chloroplast an axial plate with four lobes, two extending to 

 each cell face and forming parietal masses. (Tychoplanktont.) 



Zygospores spherical and densely covered with short mamillate- 

 conical protuberances (Ralfs). 



Cells 152 )Lt long; 70 ju broad at basal lobes of semieells, 64 /x broad 

 at median lobes, 41 ix broad at apical lobe, 21 jx broad at isthmus ; 

 apical incision 10 jx deep. 



Zygospores 148 /* in diameter; papillae 25 [x long (Ralfs). 



Mercer (rrr). 



4. EuASTRUM AFFiNE Ralfs. PI. 56, Fig. 4. 



Ann. & Mag. of Nat. Hist. 14: 191, pi. 7, figs. 3A-3B. 1844; Brit. Desm. 82, 

 pi. 13, figs. 3A-3E. 1848. 



Cells fairly large, length nearly twice the breadth, very deeply 

 constricted, sinus linear, with apex slightly inflated and outer margin 

 somewhat open, isthmus narrow; semieells truncate-pyramidate, dis- 

 tinctly five-lobed, polar lobe subincudate, with apex tumid, angles 

 broadly rounded, polar incision deep and with a slightly expanded 

 apex; incisions forming lateral lobes fairly deep, broadly rounded; 

 superior lateral lobes mamillate, about equidistant between semicell 

 apex and isthmus; inferior lateral lobes subquadrate, with angles 

 rounded and lateral margins strongly emarginate. Cell wall punctate, 

 with a transverse row of rounded protuberances at base of semicell, 

 two small protuberances just above the isthmus and a larger pro- 

 tuberance at each basal angle, with a second transverse row of two 



