52 TUFTS COLLEGE STUDIES, VOL. IV, No. 7 



TETRADBSMUS, G. M. Smith, 1913, p. 76. 



Colonies free, of four cells in two planes, the cells in one 

 plane laterally united to those in the other plane ; reproduction 

 by autocolonies. Otherwise like Scencdesmus. 



T. WISCONSINENSIS G. M. Smith, 1913, p. 76, PI. I. Cells 

 ovoid, ends sharply pointed, 4-6 X 12-15 /* Fig. f 6. Madi- 

 son, Wis., G. M. Smith. 



WESTELLA De Wildeman, 1897, p. 532. 



Families of four cells in one plane ; cells spherical or sub- 

 spherical, rarely somewhat angular, with bell-shaped chromato- 

 phore. Families united by gelatinous threads, the remnants of 

 mother cell walls, into aggregates of 20-80 cells. Vegetative 

 reproduction by division in two planes, the daughter cells 

 (autospores) escaping from the dissolving wall. 



W. BOTRYOIDES (W. West) De Wildeman, 1897, p. 532; 



Tetracoccits botryoides W. West, 1892, p. 735, PI. X, figs. 43-48. 



Cells 3. 5-8 n diam. ; aggregates 30-84 /* diam. Fig. 17. Wis., 



G. M. Smith. Europe. 



TBTRASTRUM Chodat, iSgsa, p. 114. 



Similar to Crutigenia, but with projections from the edges of 

 the cells. 



KRY TO THE Si'RciRS OF TRTRASTKIM. 



i. Cells each with one low protuberance. i. T. apiculatum. 



i. Cell* each with several fine spines. a. T. staurogeniaeforme. 



1. T. APICULATUM. (Lemtn.) Schmidle, 1900, p. 154 ; Stauro- 

 genia apiculala Lemmermann, 18983, p. 151 ; Crucigcnia apicu- 

 lala Collins, 1909, p. 170. Lake Erie, Snow; Wis, G. M. 

 Smith. Europe. 



2. T. STAUROGBNIAEFORMK (Schroder) Chodat, 1902, p. 208, 

 fig. 148; Cohniflla staurogeniaeformis Schroder, 18973, p. 273, 

 IM. XVII, figs. 5-6. Cells subsemicircular, each bearing about 

 5 hyaline spines ; cells 5-6 ft long. Fig. 18. Wis., G. M. Smith 



l-liiropt. 



Page 176, after three paragraphs of PBDIASTRUM, add 

 Within the past four years two papers have been published, 

 in which this genus has been carefully presented ; but the two 

 arrive at very different results. Nitardy, 1914, consolidates 

 species and forms relentlessly and somewhat contemptuously ; 

 Brunnthaler in Pascher, 1915, while acknowledging the great 

 variability, does not consider that we have enough data to decide 

 whit should be considered permanent and what due to environ- 

 ment. The names used in the 1909 paper have not been changed 



