Carteria cordiformis (Carter) Diesing 1866, p. 356 



PL 1, Fig. 20 

 Cells cordiform, broadest at the anterior end, which is deeply de- 

 pressed, the 4 flagella arising within the depression; somewhat smal- 

 ler but broadly rounded posteriorly. Chloroplast a thin parietal cup, 

 with 1 basal pyrenoid. Cells 16/x in diameter, 12-20/i, long. 

 Rare in tychoplankton. Mich., Wis. 



Carteria Klebsii (Dang. ) Dill 1895, p. 353 

 PI. 1, Figs. 17-19 

 Cells ellipsoid or ellipsoid-cylindric, narrower at the anterior end, 

 which is sharply rounded with a papilla around which the flagella 

 arise. Chloroplast a massive parietal cup, with 1 basal pyrenoid; 

 pigment-spot lacking. Cells 5-10/x in diameter, S-lBfx long. 

 Rare in tychoplankton. Wis. 



FAMILY PHACOTACEAE 



The flattened, unicellular biflagellates of this family, with their 

 two-valved walls, especially Phacotus lenticularis (Ehrenb.) Stein, 

 and Pteromonas angulosa (Carter) Lemm., are to be expected in 

 the central Great Lakes region, but no member of the family has 

 appeared in our collections. 



FAMILY VOLVOCACEAE 



Members of this family are colonial. The cells are characteristically 

 biflagellate and Chlamydomonas-like and are so arranged as to form 

 globose or obovoid hollow colonies or flat plates. There may be as 

 few as 4, or as many as 25,000, cells in a colony. Cell sheaths may 

 be distinct or confluent with the colonial mucilage. 



In most genera the cells of the colony are alike in size and func- 

 tion, but in the more advanced forms there is a certain amount of 

 specialization. In Pleodorina, for example, a few of the cells are dis- 

 tinctly smaller than others and have no reproductive function. In 

 Volvox some cells enlarge and become female gametes, whereas 

 others undergo division to form plates of numerous, small anthero- 

 zoids. Both kinds of gametes may be produced in the same colony 

 (monoecious) or in separate colonies (dioecious) according to spe- 

 cies. See Smith (1933, 1938, 1944), Fritsch (1935), and Pascher 

 ( 1927 ) for the morphology, reproduction, and taxonomy of this 

 family. 



[73] 



