22 WISCONSIN PHYTOPLANKTON 



1. EuASTRUM CRAssuM (De Brebisson) Kiitzing. PI. 56, Fig. 1. 

 Phycol. Germ. 135. 1845; Ealfs, Brit. Desm. 81, pi. 11, figs. 3A-3E. 1848. 



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

 sinus narrowly linear, with apex slightly inflated and outer margin 

 closed, isthmus narrow; semicells subrectangular, three-lobed, the 

 polar lobe much smaller than the lateral lobes, polar lobe broadly 

 cuneate, with apex tumid, angles broadly rounded; polar incision 

 deep, sublinear, and somewhat expanded at the apex; incisions form- 

 ing lobes open, with rounded apices and parallel sides; lateral lobes 

 very broad, margins slightly concave, superior and inferior angles 

 rounded. Cell wall finely punctate, conspicuously thickened at the 

 angles of the lobes, with three prominent hemispherical protuberances 

 across the base of the semicell, one above the isthmus and one near 

 each basal angle. Vertical view broadly oval, with a tumid inflation 

 at each pole and three less pronounced inflations on each side. Lateral 

 view of semicells narrowly pyramidate, with apices truncate and 

 angles somewhat rounded. Chloroplast an axial plate with four 

 radiating arms, two to each cell face, that form parietal masses against 

 the cell wall; pyrenoids fairly numerous and mostly in parietal por- 

 tions of chloroplast. (Tychoplanktont.) 



Zygospores unknown. 



Cells 230 IX long ; 80 /a broad at base of semicells, 62.5 fi at apex, 

 45 p. at apical lobe ; 30 ju. at isthmus ; apical incision 11.5 fi deep. 



Meta (rrr), Speese (rrr). 



2. EuASTRUM DiDELTA (Turpiu) Ralfs. PI. 56, Fig. 2. 



Ann. & Mag. of Nat. Hist. 14: 190, pi. 7, figs. 2A-2B. 1844; W. & G. S. West, 

 Monogr. Brit. Desm. 2: 15, pi. 35, figs. 3-7. 1905; Carter, Ann. of Bot. 33: 241, 

 pi. 16, figs. 63-65. 1919. 



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

 constricted, sinus linear, with apical portion inflated and outer por- 

 tion widely open, isthmus narrow; semicells narrowly truncate- 

 pyramidate, five-lobed, the lateral lobes at times reduced to strong 

 undulations ; polar lobe vertically oblong, with angles rounded, polar 

 incision fairly deep and linear but with outer portion slightly ex- 

 panded; lateral incisions very shallow and broadly rounded; lateral 

 lobes very broadly rounded. Cell wall smooth or punctate, with five 

 hemispherical protuberances on each semicell, a transverse row of 

 three at the base of the semicell, one just above the isthmus and one 

 midway between the isthmus and each basal angle ; with a second 

 transverse row of two protuberances just above and alternating with 

 those of the basal row. Vertical view elliptic, poles bearing a single 

 protuberance and sides each with five protuberances. Lateral view 

 of semicells truncate-pyramidate and with angles rounded. Chloro- 

 plast axial and with two processes extending to each cell face ; pyre- 

 noids confined to processes. (Tychoplanktont.) 



Zygospores spherical, clothed with very short papillae that are fre- 

 quently curved (W. & G. S. West). 



