WISCONSIN PHYTOPLANKTON 139 



var. Westii var. nov. PL 86, Figs. 19-20. 



Sphaerozosma excavata var. W. & G. S. West, Trans. Linn. Soc. 2nd. Ser. Bot. 

 5: 231, pi. 12, fig. 9. 1896. 



Cells with the isthmus less elongate ; lateral margins of semicells 

 ■with a single granule. (Facultative planktont.) 



Cells 10.5 [X long ; 7.5 jj. broad. 5 fi broad at isthmus ; 5 [x thick. 



Carroll (r). 



W. & G. S. AVest found but a single filament of this variety and 

 so hesitated to describe it as new. I have found it in sufficient quan- 

 tity in Carroll Lake to determine that the single granule is a constant 

 character and hence constitutes a varietal difference. 



SPONDYLOSIUM De Brebisson 1844. 



Cells usually of moderate size, ratio between length and breadth 

 variable ; united to form permanent filaments. Cells moderately to 

 deeply constricted, sinus linear to somewhat open, with an acute to 

 rounded apex; semicells usually compressed, rarely radially sym- 

 metrical, elliptic to oblong or triangular, apices flattened, at times 

 with a truncate elevation or with a slight concavity, never with apical 

 processes. Cell wall smooth or punctate, very rarely with granules 

 arranged in a definite pattern. Chloroplasts axial and usually with 

 but a single pyrenoid. Filaments with or without a gelatinous en- 

 velope. 



Zygospores usually spherical and with smooth walls. 



The older phycologists did not differentiate between Spondylosium 

 and Sphaerozosma and as a result all of the earlier described species 

 have been referred to both genera. The current conception differen- 

 tiates Spondylosium from Sphaerozosma and from Onychonema on 

 the absence of apical processes; all filamentous compressed species 

 without apical processes and with a well-defined median constriction 

 being referred to Spondylosium, S. moniliforme Lundell occupies a 

 rather analamous position since the cells of this species are triangular 

 in vertical view and not compressed. In the classification of the fila- 

 mentous species the presence or absence of a gridle-like thickening 

 at the point of cell division also plays an important role. Spondylo- 

 sium is one of the genera where there is no such thickening. 



KEY TO THE SPECIES. 



Vertical view compressed. 



Cell apices not elevated (1) S. planum 



Cell apices elevated in median portion (2) S. pulchrum 



Vertical view triangular (3) S. moniliforme 



