Although not uncommon in the plankton of lakes, this species is 

 most frequently found in the shallow water of bogs, ponds, and 

 ditches especially where the nitrogen content is high; also in hard 

 water habitats. Mich., Wis. 



Volvox tertius A. Meyer 1896, p. 188 



\yolvox mononae G. M. Smith] 



PL 3, Fig. 12 



Dioecious, relatively small colonies, 280-550/^, wide, 302-590;u, 

 long, spherical to ellipsoidal, containing 500-2000 ovoid or ellip- 

 soid cells without interconnecting protoplasmic strands, but with 

 individual sheaths which sometimes are scarcely evident. Cells 5-8;u, 

 in diameter. Chloroplast parietal, cup- or bell-shaped; pigment- 

 spot anterior and lateral; 2 (sometimes more) contractile vacuoles 

 below the point of flagella attachment. Mature coenobium contains 

 3-10-(12) daughter colonies. Eggs, 3-8 large globose cells inclosed 

 by a gelatinous sheath; antherozoid bundles 20-60 in number, con- 

 sisting of 16-32 (sometimes as many as 64) fusiform antherozoids; 

 zygotes 58-66/A in diameter, with a thick, smooth wall. 



This species is reported from Lake Monona, Wisconsin (Smith, 

 1920). In Iowa (Prescott, 1931a) it was found in one of the semi- 

 hard water lakes, forming a dense bloom, which endured for two 

 or three days in late summer when the water temperature was 

 high(28°C.). 



Mich., Wis. 



FAMILY SPONDYLOMORACEAE 



In this family the cells are compactly arranged in small colonies 

 of 8 or 16 individuals with their long axes parallel and all directed 

 forward. There is no colonial mucilage. The chloroplast is a dense, 

 parietal cup without a pyrenoid except in the genus Pascheriella 

 Korshikov (not represented in our flora). 



There are 2 or 4 flagella, 2 contractile vacuoles in the anterior re- 

 gion, and a pigment-spot, either anterior or posterior. See Fritsch 

 (1934) and Smith (1933) for a discussion of reproduction in this 

 family; also Korshikov (1923, 1924, 1928). 



SPONDYLOMORUM Ehrenberg 1849, p. 236 



Colony ovoid, of 8 or 16 pyriform cells compactly arranged in 

 tiers witiiout an evident gelatinous investment; the cells with their 

 broad apices all directed anteriorly, and having 4 long flagella which 



[79] 



