WISCONSIN PHYTOPLANKTON 89 



angle of the cell and sometimes continuing a short distance into the 

 processes; pyrenoid single and central. (Facultative planktont.) 



Zygospores spherical, with numerous straight long spines that have 

 inflated bases and apices with widely spreading bifurcations (W. & 

 G. S.West). 



Cells 95-107 /a long with processes, 46-49 fi long without processes ; 

 breadth with processes 93-118 fi, without processes 35-39 fi breadth at 

 isthmus 10 fi. 



Diameter of zygospores without spines 32 /x, with spines 60 /x (W. & 



G. S.West). 



Des Moines (rr), Horseshoe (rr), Kawaguesaga (c). 



Staurastrum gracile and S. paradoxum Meyen are closely related 

 species and ones which are inextricably confused in phycological lit- 

 erature. The description and figure of the older species (8. para- 

 doxum) might apply to many of the numerous triangular species with 

 processes at the angles. Ralfs, the discoverer of 8. gracile distin- 

 guished between the two on the basis of smaller size and divergent 

 processes of 8. paradoxum in his British Desmidieae; a work which 

 has been taken as the starting point for the nomenclature of the family. 

 Ralfs' description says nothing about the ornamentation of the body 

 of the cell of 8. gracile but the fortunate discovery of type material 

 in the Jenner herbarium at the British Museum shows that the vertical 

 view always has an intramarginal row of granules that lie in pairs 

 and have a vertical row of granules running to the cell margin from 

 each pair of granules. In this type material the processes are very 

 short (Text Figs. 9A-9C). No specimens exactly like this were found 

 in the plankton catches of the G. S. West collections, although speci- 

 mens from Norwegian lakes in the Huitf eld-Kaas collection were quite 

 like them (Text Figs. 9F-9G). After examining the series found in 

 the British plankton, as contained in the G. S. West collection, I feel 

 that shape of the semicells and length or divergence of the processes 

 cannot be used in distinguishing between >S^. gracile and 8. paradoxum 

 and that on these bases the two species should be united. The intra- 

 marginal row of granules in pairs (the apical verrucae of the front 

 view) is a feature which separates the two and all specimens with 

 these verrucae should be referred to 8. gracile. 



The species is undoubtedly of much more limited distribution than 

 has been supposed and many references to it are unquestionably deal- 

 ing with 8. paradoxum. The Wisconsin specimens have long divergent 

 processes and look, in vertical view, like the specimens found in Loch 

 Doon, Scotland, by W. & G. S. West which they called a ' ' very large 

 form" (Text Fig. 9D). 



