20 WISCONSIN PHYTOPLANKTON 



processes. Cell wall smooth. Chloroplast axial, with longitudiiial 

 plates extending from semicell base to apex; pyrenoids forming a 

 median row and fairly numerous. (Tychoplanktont.) 



Zygospores unknown. 



Cells 480-504 fi long ; 30-41 /a broad at basal whorl (with verrucae) , 

 25-28 ju, broad at apical whorl (with verrucae), 13-21 /x broad just 

 above apical whorl. Distance between ends of apical processes 

 31-48 fjL. 



Des Moines (rrr), Little Doctor (rrr). 



A much rarer species than T. gracile and differing in the nature 

 of the transverse whorls of verrucae. Figure 9 is a transition form 

 between the two in which the base of the semicell is typical verti- 

 cillatum and the apex gracile. 



TETMEMORUS Ralfs 1844. 



Cells usually fairly large, length 2-8 times the breadth, median 

 constriction slight to fairly deep but always well defined, sinus always 

 open; semicells straight, cylindrical to subfusiform, with poles some- 

 what compressed and having a very conspicuous vertical incision, 

 incision generally linear and with a slightly inflated apex. Cell wall 

 smooth, punctate, or minutely scrobiculate. Chloroplasts axial and 

 with 8-10 vertical radiating plates that are simple or bifurcate at 

 the point where they reach the cell wall ; pyrenoids fairly numerous, 

 spherical to bacillar and arranged in a linear series along the central 

 axis. 



Zygospores spherical to rectangular, with smooth walls. 



The elongate cells with apical incisions separate this genus from 

 all others found in Wisconsin lakes. 



Tetmemorus Brebissonii (Meneghini) Ralfs. PI. 55, Fig. 10. 



Ann, & Mag. of Nat. Hist. 14: 257, pi. 8, figs. lA-lD. 1844; Nordatedt, Lunds 

 Univ. Arsskr. 9: 39. 1873. 



Cells large, length 5-6 times the greatest breadth, fairly deeply 

 constricted, sinus with a subacute apex and outer margin widely open ; 

 semicells cylindrical, somewhat attenuated towards the poles, basal 

 angles very broadly rounded; apex rounded, with a very deep linear 

 incision in the median portion. Lateral view of semicells compressed 

 in the polar region and giving the whole cell a subfusiform appear- 

 ance. Cell wall slightly thickened near the outer margins of the 

 polar incisions; entire wall covered with numerous punctae ar- 

 ranged in vertical rows running from semicell base to apex. Chloro- 

 plasts axial, with about eight vertical radiating plates that terminate 

 in broad parietal forks at the cell wall; pyrenoids axial and variable 

 in shape. (Tychoplanktont.) 



Zygospores spherical, with smooth walls (Nordstedt). 



Cells 226-264^ long; 39^5 fi broad at base, 25-31 /x at apex, 

 21-27.5 fi at isthmus ; apical incision 10 fi deep. 



Zygospores 80 /x in diameter (Nordstedt). 



Duck (rrr), Tank (rrr). 



