WISCONSIN PHYTOPLANKTON 107 



also with an intramarginal row of tridenticulate verrucae; processes 

 with concentric rings of granules. (Tychoplanlitont.) 



Zygospores unknown. 



Cells 60 fi long with processes, 34 ix long without processes ; breadth 

 with processes 88 ix, without processes 20 /x; breadth at isthmus 11.5 fi. 



Little Doctor (rrr). 



The species has not been observed since it was described by William 

 West. In reexamining type material in the G. S. West collection I 

 have noted a ring of granules at the base of the semicells, a feature 

 which was overlooked in the original description. A figure of an 

 Irish specimen is also given for comparison with the Wisconsin 

 material. 



var. CRAssuM W. & G. S. West. PI. 79, Figs. 13-15. 



Trans. Liun. See. 2nd. Ser. Bot. 5; 265, pi. 17, fig. 14. 1896. 



Semicells with a much larger ring of granules on the central pro- 

 tuberance; apical verrucae with denticulations of the same size. 

 Vertical view with truncate projection much larger than that of the 

 type. (Facultative planktont.) 



Cells 42-50 /x long with processes, 30-33 fi long without processes ; 

 breadth with processes 58-70 /x, without processes 18-21 [x ; breadth 

 at isthmus 7.5-8.5 /t; thickness 20 /x. 



Horseshoe (r). 



S. natator can be separated from other biradiate species by the 

 central protuberance, a feature which is much more pronounced in 

 the variety crassum. When due allowance is made for the defects of 

 draftmanship frequently found in the drawings of Wolle there is a 

 possibility that 8. natator var, crassum is identical with his 8. minne- 

 apoliense (Bull. Torr. Bot. CI. 12: 5, pi. 47, figs. 11-13. 1885). The 

 front view of 8. minneapoliense is, as W. & G. S. West have pointed 

 out, quite different from that of 8. natator var. crassum. 



43. Staurastrmn urinator sp. nov PI. 79, Figs. 16-18. 



Cells fairly large, breadth (with processes) about one and a 

 quarter times the length, slightly constricted, sinus a small acute- 

 angled indentation with a blunt apex, isthmus relatively broad ; 

 semicells campanulate with the lateral margins of the bases semi- 

 circular and generally bearing an erect spine in the median portion; 

 apices flattened and with three somewhat emarginate verrucae ; 

 angles continued in long slightly attenuated processes that terminate 

 in three short divergent spines, superior and inferior margins of 

 processes with conspicuous teeth that point away from the body 

 of the semicell, median area of processes smooth, processes out- 

 wardly divergent. Vertical view narrowly elliptic, lateral margin 



