WISCONSIN PHYTOPLANKTON 27 



semicells, one above the isthmus and one on each lateral lobe. Vertical 

 view elliptic, with poles rounded and three very prominent protuber- 

 ances on each side. Lateral view of semicells subrectangular, with 

 bases inflated, polar angles rounded, and apices concave. (Tycho- 

 planktont. ) 



Zygospores unknown. 



Cells 54-56 /a long ; 41-43 /a broad at base of the semicells, 20 fi at 

 polar lobe, 12.5 /* at isthmus. 



Muskallonge (rrr). Tank (rrr). 



11. EuASTRUM VERRUCOSUM Ehreubcrg. 



A.bh, d. k. Akad. d. Wiss. zu Berlin 1833: 247. 1835; Ealfs, Brit. Desm. 79, pi. 11, 

 figs. 2A-2D. 1848; Carter, Ann. of Bot. 33: 245, pi. 17, figs. 90-92. 1919. 



Cells of medium size, length slightly greater than the breadth, very 

 deeply constricted, sinus with inner half sublinear and apex slightly 

 inflated, outer half gradually opening outwards, isthmus very nar- 

 row; semicells truncate-pyramidate, distinctly three-lobed, the polar 

 lobe smaller than the lateral lobes, polar lobe broadly cuneate, with 

 angles rounded and polar incision reduced to an emargination of the 

 polar lobe ; incisions forming the lobes deep, sublinear, with rounded 

 apices and widely open outer extremities; lateral lobes broadly 

 cuneate, divided into two lobules by a very deep emargination, supe- 

 rior lobule suberect, inferior lobule horizontally disposed, lobelets 

 broadly rounded. Cell wall distinctly granulate, with granules more 

 pronounced at angles of lobes, bases of semicells with a very large 

 protuberance just above the isthmus and flanked by a smaller pro- 

 tuberance in each of the lateral lobes, protuberances, especially the 

 central one, furnished with somewhat elongate verrucae arranged in 

 concentric circles. Vertical view compressed-hexagonal, with the 

 angles rounded and a conspicuous protuberance in the center of the 

 longer sides, cell outline granulate. Lateral view of semicells urn- 

 shaped, with a deep emargination at the apex. Semicells with two 

 axial chloroplasts, each chloroplast with 4-5 irregular ridges radiat- 

 ing to front and sides of cell wall; pyrenoids single and central in 

 each chloroplast. 



Zygospores unknown. 



Cells 107 /t long; 108 /. broad (Ralfs). 



Not found in the plankton of Wisconsin lakes. 



var. REDUCTUM Nordstedt. PI. 56, Fig. 10. 

 Lunds Univ. Arsskr. 16: 9, pi. 1, fig. 14. 1880 (sep.). 



Cells smaller, sinus linear, with apex inflated and outer margin 

 open ; polar lobes subrectangular, incisions forming lobes more widely 

 open; lateral lobes only slightly emarginate. (Tychoplanktont.) 



Cells 58 fi long ; 52 fi broad at base of semicells, 23 /x at apical lobe ; 

 12 fi at isthmus. 



Devils (rrr), Little Doctor (rrr). 



The sinus, lateral incision, shape of the polar lobe and the d^ree 

 of indentation of the lateral lobes differentiate this variety. 



