44 WISCONSIN PHYTOPLANKTON 



ornamentation. Vertical view with sides parallel and ends rounded 

 but terminating in an acute point. Lateral view of semicells oblong, 

 with vertical sides slightly concave, apex rounded and minutely 

 trispinate. 



Fig. 4. Micrasterias conferta Lundell (x500). Prom a plankton specimen col- 

 lected at Figgenldin, Norway, by H. Huitfeldt-Kaas. 



Zygospores unknown. 



Cells 100 fi long ; 87.5 fi broad at the basal lobes, 40 n at apex of 

 apical lobe ; 17.5 {x. broad at isthmus. 

 Not found in the plankton of Wisconsin lakes. 



var. HAMATA Wolle. PI. 59, Figs. 6-7. 



Bull. Torr. Bot. CI. 10: 19, pi. 27, fig. 1. 1883; W. & G. S. West, Trans. Linn. 

 Soc. 2nd. Ser. Bot. 5: 241, pi. 14, figs. 8-9. 1896; Monogr. Brit. Desm. 2: 90, pi. 

 43, figs. 10-11. 1905. 



Incision forming polar lobes more widely open, lateral margin of 

 polar lobe with a semicircular excavation near the apex that causes 

 the lateral margins to be subparallel. Chloroplast extending to mar- 

 gins of lobes, incision in polar lobe of chloroplast shallow, with two 

 longitudinal ridges extending from polar apex to nucleus; pyrenoids 

 8-10. (Tychoplanktont.) 



Cells 75-92^ long; 73-82 ^u broad at base of semicells, 34-37/1 

 at apex of polar lobe ; isthmus 12-13 /x broad. 



Des Moines (rrr). 



The variety and the type are distinguished by the degree of ex- 

 pansion in the upper part of the polar lobe. In size, general contour, 

 and depth of incision the species resembles M. papillifera De Brebis- 

 son but the two differ in the shape of the polar lobe. The variety 

 differs from the type in the curvature of the upper part of the lat- 

 eral margins of the polar lobe, a curvature which causes the incision 

 to be broader and which gives the polar lobe an exserted appearance. 

 W. & G. S. West have shown the close relationship between the type 

 and the variety and have figured specimens with one semicell typical 

 and the other with the polar features of the variety. 



