WISCONSIN PHYTOPLANKTON 79 



This species is related to the Staurastrum teliferum-setigerum 

 group of species but differs in having the spines at the angles shorter 

 and the same size as those of the cell body. The regular arrangement 

 of the spines on the cell body in the vertical view is also more pro- 

 nounced in this species. 



The spines in the few specimens from Tank lake were much smaller 

 than those from the other lakes but they were arranged in the same 

 regular pattern (Figs. 16-18). 



19. Staurastrum setigerum Cleve. PI. 70, Figs. 19-25. 



of vers. Kgl. Sv. Vet.-Ak. Forh. 20: 490, pi. 4, fig. 4. 1864; Lundell, Nova Acta 

 Eeg. Soc. Sci. Upsaliae 3 ser., 8: 64, pi. 4, fig. 3. 1871; E07 & Bisset, Ann. 

 Scottish Nat. Hist. 1893: 243, pi. 3, fig. 9. 1893. 



Cells of medium size, length (without spines) equal to the breadth, 

 deeply constricted, sinus open but with an acute apex, isthmus nar- 

 row; semicells subelliptic, with the central portion of the rounded 

 apex flattened, lateral margins truncate and with two stout divergent 

 spines; dorsal margin with a stout spine near the angles and four 

 more delicate spines on the apex; face of semicells with a transverse 

 row of long delicate spines. Vertical view triangular, with the sides 

 retuse and the angles acute; angles with three stout spines in the 

 same vertical plane, two at the angle and one a short distance back 

 from the angle; sides with four more delicate spines of the same 

 length on each lateral margin, margin retuse between spines ; body 

 of semicells with another curved row of similar spines within the 

 margin and one or two spines continuing the line formed by the 

 stout spines on the angles. Chloroplasts axial, with a small central 

 mass and lobes very deeply incised to form two arcuate plates that 

 run to each angle; pyrenoid single. (Facultative planktont.) 



Zygospores unknown. 



Cells 52-57 /* long with spines, 42-48 /^ long without spines ; breadth 

 with spines 60-67 /x, without spines 42-55 ju; breadth of isthmus 

 11.5-12.5 /* ; length of stout spines 8-13 /x, of delicate spines 5-11 /x. 



Beaverdam (sss). Fish (s), Nicaboyne (rrr). 



The vertical view of this species shows more of the distinctive fea- 

 tures than does the front view. The three stout spines forming a 

 vertical row at the angle and the four delicate spines on each margin 

 are quite constant features. The arrangement of the spines within 

 the margin is subject to considerable variation and the description 

 of their arrangement given above is found only in symmetrically de- 

 veloped specimens; the number of interior spines is also subject to 

 variation. An atypical specimen is shown in Figure 24 where there 

 are accessory stout spines at the angles and a large number of spines 

 at the center of the cell. 



