WISCONSIN PHYTOPLANKTON 49 



incisions narrow and extending slightly more than half the distance 

 from the periphery to the cell center ; polar lobe with lateral margins 

 subparallel in basal portion and somewhat outwardly divergent in 

 the apical portion, polar apex not projecting beyond the lateral lobes 

 and with a fairly deep, acute or rounded emargination at the center; 

 lateral angles emarginate to bifid, central emargination at times 

 flanked on either side by an erect spine; lateral lobes of approxi- 

 mately the same size, with three series of incisions, the depth of each 

 successive incision approximately half that of the preceding series, 

 ultimate lobelets with outer face slightly emarginate; face of cell 

 with a transverse row of three large projections just above the 

 isthmus, the central conical projection being flanked on either side 

 by an outwardly curved projection with a mamillate to a truncate 

 apex and with two spines ; primary lateral lobules with a conical tooth 

 at the base, secondary lobules sometimes each with a similar but 

 smaller tooth; polar lobe with a basal tooth and sometimes two sub- 

 apical teeth ; teeth always directed outwards and lying in a semicircle 

 that follows the general contour of the semicell. Vertical view nar- 

 rowly fusiform, with a central conical projection and on either side 

 of this an emarginate projection that faces the poles. Lateral view 

 of semicells narrowly pyramidate, with apex truncate and bases 

 rounded. Chloroplast extending into the ultimate lobelets, portion in 

 polar lobe deeply emarginate, with longitudinal ridges following the 

 major incisions; pyrenoids 20-40. (Tychoplanktont.) 



Zygospores spherical, with stout furcate spines (W. & G. S. West). 



Cells 225 IX long; 192 /x broad at the base of the semicells; 47.5 ^ 

 broad at the apex of the polar lobe ; 42.5 fi broad at the isthmus. 



Meta (rrr). 



The species is readily distinguished from the other deeply incised 

 ones by the basal projections of the semicells and the arc of teeth at 

 the base of the lobelets. These characters are, however, subject to 

 great variation and individuals may be found where the prominence 

 of these features is greatly reduced and where the central basal pro- 

 tuberance and certain of the subperipheral teeth are lacking. 



10. MicRASTERiAS ToRREYi Bailey. PI. 62, Fig. 2. 



in Ralfs, Brit. Desm. 210, pi. 35, fig. 5. 1848; WoUe, Desm. U. S. 108, pi. 30, 

 figs. 1-8. 1884. 



Cells very large, rectangular in outline, length and breadth about 

 equal, very deeply constricted, sinus linear and with outer portion 

 somewhat open, isthmus very narrow; semicells five-lobed, incisions 

 deep, with apices sublinear and outer portion acute-angled; polar 

 lobe arising near the isthmus, lateral margins of the polar lobe sub- 

 parallel but widely divergent near the apex, apical margin with a 

 conspicuous median emargination that gives it a concave appearance, 

 median emargination flanked on either side by a simple mamillate 

 swelling; polar angles fairly acute and simple, very rarely emar- 

 ginate; lateral lobes of unequal size, the superior lateral lobe very 

 deeply incised and one of the lobelets, usually the one adjacent to 



