88 



WISCONSIN PHYTOPLANKTON 



This organism shows such a strong resemblance to S. protectum in 

 shape of the semicells, divergent spines on the processes, and apical 

 verrucae that I feel it should be considered a variety. It differs pri- 

 marily in the rings of granules on the processes and a lack of subapical 

 verrucae. 



27. Staurastrum gracile Ralfs. PI. 73, Figs. 16-18. 



Ann. & Mag. of Nat. Hist. 15: 155, pi. 11, figs. 3A-3B, 1845; Brit. Desm. 136, 

 pi. 22, figs. 12A-12D. 1848; W. & G. S. West, Jour. Eoy. Micr. Soe. 1897: 495, 

 pi. 6, fig. 27. 1897; W. & G. S. West, Jour. Linn. Soc. Bot. 35: 529. 1903. 



Cells of medium size, length generally greater than the breadth 

 (without processes), deeply constricted, sinus widely open and with 

 an acute apex, isthmus fairly narrow; semicells broadly triangular to 

 cyathif orm ; dorsal margin slightly concave to somewhat convex, with 

 a row of small emarginate verrucae, apex of semicell body sometimes 

 with a short vertical row of granules below each apical verruca ; angles 

 continued in hollow processes of variable length, processes slightly at- 

 tenuated, with transverse rings of granules and terminating in three 

 or four small spines, processes parallel to widely divergent. Vertical 

 view triangular, with sides of body of the cell slightly concave and 

 angles continued in straight processes; cell body with an intramar- 



Fig. 9. staurastrum gracile Ealfs (x600). Figs. A-C from type material in the 

 Jenner Herbarium of the British Museum of Natural History; Fig. D a plankton 

 specimen collected in Loch Doon, Scotland, by W. & G. S. West ; Figs. E-G plank- 

 ton specimens from Norwegian lakes. Fig. E from Orrvandet, Figs. F, G from 

 Lemonsj0en. 



ginal row of pairs of granules (the verrucae of the front view) and 

 at times short rows of granules at right angles to the sides of the cell, 

 center of the cell without ornamentation; processes with transverse 

 rings of granules and trispinate or quadrispinate. Chloroplast with 

 a fairly small axial mass and two laminate blades running to each 



