26 WISCONSIN PHYTOPLANKTON 



rounded. Cell wall smooth, with a triangle of three elongate verrueae 

 just above the isthmus and two small granules on either side of the 

 apical incision and at basal angles of the semicells. Vertical view 

 narrowly elliptic, with a truncate protuberance on either side midway 

 between the poles. Lateral view of semicells ovate and with a pro- 

 tuberance on either side of the base. Chloroplast a massive axial plate 

 with two lobes extending towards each cell face; pyrenoid central 

 and single. (Tychoplanktont.) 



Zygospores spherical, with fairly short straight spines that have 

 blunt apices (W. & G. S. West). 



Cells 36 fi long ; 25 /x broad at base of semicells, 11.3 fi at apex, 

 5 ju. at isthmus; apical incisions about 5 [x deep. 



Zygospores (without spines) 20-29 ju, in diameter; spines 7.5-9.5 /m 

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



George (rrr), Jones (rrr). 



9. EuASTRUM DivARiCATUM Lundell. PI. 56, Fig. 9. 

 Nova Acta Eeg. See. Sci. Upsaliae 3 Ser., 8: 21, pi. 2, fig. 5. 1871. 



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

 deeply constricted, sinus linear, with apical portion slightly inflated, 

 isthmus narrow; semicells truncate-pyramidate, rather distinctly 

 three-lobed, the polar lobe somewhat smaller than the lateral lobes; 

 polar lobe transversely oblong, with apex tumid, angles obtuse and 

 each furnished with a divergent spine, polar incision fairly deep 

 and open; lateral lobes broadly triangular and with rounded angles, 

 with two or three marginal spines of variable length. Cell wall 

 smooth, with a triangle of short linear verrueae above the isthmus 

 and a large rounded granule on either side of the polar incision, about 

 four smaller granules within the margins of the lateral lobes. Verti- 

 cal view elliptic, with a short spine at each pole and with sides crenu- 

 late, median portion of each side with a short truncate protuberance. 

 Lateral view of semicells sublanceolate, with a protuberance on either 

 side of the base. (Tychoplanktont.) 



Zygospores unknown. 



Cells 43 IX long ; 38 ju. broad at base of semicells, 20 /x at apex, 

 7.5 fi at isthmus; apical incisions about 5 fi deep. 



Muskallonge (rrr). 



10. EuASTRUM GEMMATUM Dc Brcbisson. PL 57, Figs. 1-2. 



in Meneghini, Linnaea 14: 221. 1840; Ealfs, Brit. Desm. 87, pi. 14, figs. 4A-4E. 

 1848. 



Cells fairly small, length about one and half times the breadth, 

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

 widely open, isthmus narrow; semicells distinctly three-lobed, polar 

 incision reduced to a broad emargination ; lateral incisions deep, 

 broadly open and with rounded apices; lateral lobes subquadrate, 

 with angles broadly rounded and lateral margins deeply retuse. Cell 

 wall finely granulate, with granulation prominent at angles of polar 

 and lateral lobes and on the three protuberances at the bases of the 



