COSMARIUM. 127 



Vertical view elliptic. Cell-wall colourless and smooth. 

 Length 11/i; breadth 8^; breadth of isthmus 2 /LI thick- 

 ness 5 [4." 



We have also referred a minute species of Cosmarium col- 

 lected near Tliirsk, N. Yorks., to Archer's species, but the 

 identification is necessarily very uncertain (vide West & Gr. S. 

 West, ' Alga-fl. Yorks/ 1900, p. 73). The semicells were 

 somewhat flattened at the apex, and the zygospore was 

 rhomboid-elliptic. Length 8*4 JJL ; breadth 8'5 /LI ; breadth of 

 isthmus 2'7 /*; length of zygosp. 12 JJL', breadth of zygosp. 10 in. 



COSMARIUM WRIGHTIANUM Arch, in Ann. Mag. Nat. Hist, xi, 

 1883, p. 208; Cooke, Brit. Desm. 1887, p. 187. "Minute, 

 smooth; semicells oblong-elliptic, ends somewhat retuse; 

 but this feature is so slight as to be very readily over- 

 looked/' Zygospore " tetrahedral, the angles bluntly rounded/' 

 Size . . . . ? 



Hcib. Ireland. 



EXCLUDED SPECIES. 



COSMARIUM PLATYISTHMUM Arch, in Ann. Mug. Nat. Hist, xi, 

 1883, p. 215; Cooke, Brit. Desm. 1887, p. 187; De Toni, Syll. 

 Alg. 1889, p. 1034. Ursinella platyisthma Kuntze, Revis. gen. 

 plant. 1891, p. 925. This Alga has recently been shown to 

 belong* to the Protococcaceas (or Autosporaceas) and should 

 be known as TETKAEDRON PLATYISTHMUM (vide Gr. S. West in 

 < Journ. Linn. Soc. bot/ xxxviii, 1908, pp. 286, 287, t. 21, 

 f. 36-39). 



