WISCONSIN PHYTOPLANKTON II5 



the size of the cells. Although the processes resemble those of 

 tetragonal and pentagonal forms of S. Ophinra Lundell it differs in 

 the more delicate body of the cell, inflation of the base of the semi- 

 cells, lack of a basal ring of conical spines, and most of all in the 

 totally different ornamentation of the cell apices. 



50. Staurastrum Ophiura Lundell. PI. 81, Figs, 3-4. 

 Nova Acta Keg. Soc. Sci. Upsaliae 3 Ser., 8: 69, pi. 4, fig. 7. 1871. 



Cells very large, length two and half to three and a half times the 

 breadth (without processes), slightly constricted, sinus small and 

 semicircular, isthmus broad ; semicells cyathif orm, with strongly con- 

 vex apices, base of semicells with a ring of stout conical verrucae with 

 rounded apices and with four or five of these verrucae visible in a 

 front view; superior portion of semicells prolonged into gracefully 

 attenuated subparallel to convergent processes, upper surfaces of 

 processes more sharply crenulate than the lower, ends of processes 

 trispinate, median area of processes with bifid verrucae on the portion 

 near the body of the cell and simple spines on the apical portion ; 

 rounded portion of semicell above the processes with a bifid verruca 

 midway between apex and the insertion of the processes. Vertical 

 view seven-rayed (rarely six- or eight-rayed), with rays gradually 

 attenuated and trispinate, with lateral margins at base of processes 

 bearing elongate emarginate to bifid verrucae and apical portion with 

 simple spines, processes with a median row of simple spines ; body of 

 semicell with two broad emarginate verrucae at the margin between 

 the insertion of each pair of processes ; central portion of body with 

 a ring of elongate bifid verrucae, the number of verrucae correspond- 

 ing to the number of processes, verrucae alternating with, not oppo- 

 site, the processes. (Tychoplanktont.) 



Zygospores unknown. 



Cells 75-82 fi long ; breadth with processes 115-160 fx, without 

 processes 32-35 fi ; breadth at isthmus 23-25 fi. 



Bass (rrr), Horseshoe (rrr), Lake of the "Woods (rrr), Muskallonge (rrr). 



This conspicuous and unique alga varies somewhat in the number, 

 length, and convergence of the processes. In the Wisconsin plankton 

 seven-rayed cells are the rule whereas in the English plankton eight- 

 and nine-rayed specimens predominate. There is likewise variation 

 in the ornamentation of the cell and the verrucae forming the central 

 ring at the apex may be near the margin or the center. Lundell 

 states that these verrucae are quadrifid but I have only noted bifid 

 apical verrucae. Likewise the two emarginate verrucae between each 

 pair of rays may be within the margin of the cell or projecting be- 

 yond it. The lateral verrucae of the processes are generally bifid, 

 though cases have been found in which they are reduced to simple 

 spines. 



