WISCONSIN PH7TOPLANETON 33 



MERISMOPEDIA PUNCTATA Meyen. PI. 2, Fig. 3. 



Arch. f. Naturgescb. 5*: 67. 1839; Kutzing, Tabulae Phycol. 5: 18, pi. 38, ftp. 3. 

 1855. 



Colonies small, with the cells some distance from one another but 

 regularly arranged in rectilinear series. Cells spherical to broadly 

 ovoid or hemispherical. Cell contents homogeneous, grey to pale blue- 

 green. (Tychoplanktont). 



Diam. cells 2.5-3.5 /*. 



Big Bass (rrr). 



MERISMOPEDIA TENUISSIMA Lemmermann. PI. 2, Fig. 2. 



Bot. Cent. 76: 154. 1898; Forschungsbr. a. d. Biol. Stat. zu P16n 7: 132, pi. 1, 

 fig. 21. 1899. 



Colonies rectangular, free-floating, generally with 16-100 cells lying 

 close together. Rectilinear arrangement of cells soon breaking down 

 and not evident when there are more than 32 cells in a colony. Col- 

 onies distorted when of any size. Cells spherical to ovoid, hemispheri- 

 cal for some time after division. Individual sheath of cells distinct 

 or confluent with colonial envelope. Cell contents homogeneous; grey 

 to pale blue-green. (Facultative Planktont). 



Diam. cells (without sheath) 1.5-2 jn. 



Camp (rr), Little Doctor (rr), Long (3) (r), Mary (rr). 



The irregular cellular arrangement is very common in older colonies 

 and is not due to the size of the colony, since the species is one of the 

 smallest of the genus, but to irregularities in cell division. 



COELOSPHAERIUM Nageli 1849. 



Colonies microscopic, free-floating; spherical, ellipsoid, reniform, or 

 irregular ; enclosed by a delicate, hyaline, homogeneous or radially fibril- 

 lar, gelatinous envelope. Cells spherical, ovoid, ellipsoid, sub-pyriform 

 and arranged in a single layer to form a hollow sac just beneath the 

 periphery of the colonial envelope. Cell contents homogeneous and 

 grey to bright blue-green ; or reddish and containing numerous pseudo- 

 vacuoles.* 



Reproduction by vegetative cell division in three directions. 



*These structures, which are also called gas vacuoles, are found in certain 

 plankton species of the Myxophyceae. They are minute bodies, which are 

 reddish through their refractive power, that occur in large numbers in all 

 cells of the colony. Various functions have been ascribed to them, the most 

 probable being a means of protection against too intense light, or a giving of 

 greater buoyancy to the colony. 



