WISCONSIN PHYTOPLANKTON 137 



semicells and interlock with corresponding processes from adjacent 

 cells; processes frequently simple granules, never overlapping the 

 adjacent cells. Cells compressed, generally moderately constricted 

 and with an open sinus; semicells elliptic to oblong, lateral margins 

 smooth or granulate, never with spines. Vertical view usually elliptic 

 and lateral view of semicells subspherical. Cell wall smooth, punc- 

 tate, or with granules arranged in a definite pattern. Chloroplasts 

 axial and with one pyrenoid. 



Zygospores generally spherical and with smooth or spinate walls. 



The genus stands between Spondylosiuni and Onychonema. The 

 short interlocking apical processes or granules are the most prominent 

 diagnostic character. It is difficult to differentiate between many 

 Spondylosiuni and Sphaerozosma species since these granules may be 

 greatly reduced and easily overlooked. 



KEY TO THE SPECIES. 



Apical processes somewhat elongate (1) S. Aubertianum 



Apical processes simple granules. 



Lateral margins of cells granulate (3) S. excavatum 



Lateral margins of cells smooth (2) S. exiguum 



1. Sphaerozosma Aubertianum W. West. 



Jour, of Bot. 27: 206, pi. 291, fig. 17. 1889; Jour. Liun. Soe. Bot. 29: 115, pi. 19, 

 lig. 1. 1892; W. & G. S. West, Trans. Linn. Soc. 2nd. Ser. Bot. 5: 230, pi. 12, 

 ■figs. 7-8. 1896. 



Cells of moderate size, breadth somewhat greater than the length, 

 fairly deeply constricted, sinus with the apex acute and the outer 

 margin widely open, isthmus fairlj^ narrow; semicells elliptic to 

 oblong-elliptic, with lateral margins conspicuously flattened, ventral 

 and dorsal margins with the same degree of curvature; apical proc- 

 esses reduced to two small elongate granules that lie some distance 

 from each other ; lateral margins of semicells with two small granules 

 on each side. Lateral view of semicells subspherical, the pairs of 

 granules on side of semicell forming a linear series. 



Zygospores spherical to subspherical, with numerous long spines 

 that have broadly conical bases and simple acute apices (W. & G. S. 

 West). 



Cells 16.5-19 IX long ; 18-23 /x broad ; isthmus 5-8 jx broad ( W. 

 West). 



Diameter of zvgospores with spines 37.5-42 ju,, without spines 

 19-24/. (W. &G. S. West). 



Not found in the plankton of Wisconsin lakes. 



var. Archerii (Gutwinski) W. & G. S. West. PI. 86, Fig. 16. 

 Trans. Linn. Soc. 2nd. Ser. Bot. 5: 230. 1896. 



Sphaerozosma Archeri Gutwinski, Bot. Cent. 43: 66. 1890; Sprawozd. kom 

 fizyjogr. Akad. Umiej. w Krakowie 27: 29, pi. 1, fig. 4. 1891. 



Cells larger; semicells transversely elliptic and with the lateral 

 margins more rounded. Face of semicells with two transverse rows 



