WISCONSIN PHYTOPLANKTON 25 



apex strongly elevated, polar incision very deep, obversely ovate and 

 with outer margin almost closed, lateral margins of polar lobe with 

 a small spine at the base; incisions between lobes widely open and 

 with broadly rounded apices ; lateral lobes subquadrate, with margins 

 retuse in the median portion, angles rounded and each bearing a pair 

 of short sharp divergent spines. Cell wall smooth, thickened at the 

 polar angles and at the angles on either side of the apical incision, 

 with a central protuberance above the isthmus and scattered granules 

 on either side of the polar incision and at the base of the semicells. 

 Vertical view elliptic, with poles strongly truncate and a protuberance 

 in the middle of the sides. Lateral view of semicells ovate, with a 

 small protuberance at the bases. (Tychoplanktont.) 



Zygospores unknown. 



Cells 63 [X. long ; without spines 37 /x broad at base of semicells, 22 /x 

 at apex ; with spines 40 /i, broad at base of semicell, 35 /x at apex ; 8 ^ 

 broad at isthmus ; apical incision 7.5 /x deep. 



Little Doctor (rrr). 



7. EuASTEUM PULCHELLUM De Brebisson. PI. 56, Fig. 7. 



Mem. d. 1. Soc. imp. d. sc. nat. de Cherbourg 4: 124, pi. 1, fig. 5. 1856; W. & 

 G. S. West, Monogr. Brit. Desm. 2: 46, pi. 38, figs. 14-15. 1905. 



Cells small, length about one and a quarter times the breadth, 

 deeply constricted, sinus linear, with outer portion slightly open, 

 isthmus narrow; semicells truncate-pyramidate, the division into 

 three lobes very poorly defined, polar lobe transversely oblong, with 

 apex slightly concave and polar incision quite broad, angles acute 

 and continued in short widely divergent spines; incisions forming 

 lobes broad, very shallow depressions; lateral lobes broadly rounded 

 and with profile bearing 3-4 short sharp spines. Cell wall with a 

 triangle of three elongate verrucae just above the isthmus, a con- 

 spicuous rounded granule at either side of the apical incision, and a 

 few scattered spines within the margins of the lateral lobes. Vertical 

 view oblong-elliptic, with short spines in the polar region and a con- 

 spicuous truncate protuberance in the middle of each side. Lateral 

 view of semicells narrowly pyramidate-ovate, with apex rounded and 

 bearing a single erect spine, bases with a conspicuous truncate pro- 

 tuberance. (Tychoplanktont.) 



Zygospores unknown. 



Cells 26 /x long; 23 /ix broad at base of semicells, 16 /x at apex, 

 6.5 /x at isthmus ; depth of apical incision 2.5 /u. 



George (rrr). 



8. EuASTRUM ELEGANS (Dc Brebissou) Kiitzing. PI. 56, Fig. 8. 



Phycol. Germ. 135. 1845; W. & G. S. West, Monogr. Brit. Desm. 2: 48, pi. 38, 

 figs. 16-21. 1905. 



Cells small, length about one and a half times the breadth, deeply 

 constricted, sinus linear and with apex expanded, isthmus narrow; 

 semicells ovate, not incised to form lobes, apex uncinate and with 

 upper margin very strongly inflated and angles apiculate; apical 

 incision deep and narrowly V-shaped; basal angles very broadly 



