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THE AMERICAN NATURALIST [Vol. LIV 



M. longifilum (Fig. 1) seems to be the most common 

 species in the waters about Ithaca, N. Y., and New Haven, 

 Conn., though M. repetans (Fig. 2) was often seen. The 

 former is the larger, the more hyaline, and furthermore 

 possesses at least one quite prominent contractile vac- 

 uole. No difference in the length of the flagellum in the 

 two species could be observed. 



Genus Cekcobodo Kraasilstschik. 



Body changeable in form from almost globular to elon- 

 gate, with the posterior extremity usually more or less 

 drawn out, frequently acuminate. This latter form is 

 the one under which the species most frequently appears. 

 The two flagella arise from the anterior end of the body. 

 Often an amoeboid form of body is assumed, and locomo- 

 tion is effected by blunt pseudopodia. 



Because of its instability of form, the one species which 

 is the most common has been relegated successively to 

 the genera Dimastig amoeba, Dimorpha, and Cercobodo. 

 The single contractile vacuole is usually present and 

 prominent. The one species observed seems to conform 

 to the Cercobodo mutabilis of Stokes (Fig. 3). 



Genus Ceecomonas Dujardin. 



Body globular to ovate, pointed at the anterior and 

 posterior extremities, from each of which arises a long 

 Hagvllnm, the posterior of these being the stouter, a trifle 

 the shorter and less motile. The pseudopodia, which 

 are occasionally produced, are not as well defined as 

 those in the two preceding genera, and are limited to the 

 posterior fourth of the body. These were not frequently 

 seen. 



Two species are fairly common: C. longicauda (Fig. 

 4), and C. crassicauda (Fig. 5). They may be distin- 

 guished by their difference in size. 



Genus Physomonas Kent. 



Body changeable in form, though not possessing p>''ii- 

 dopodia, and varying from elongately ovoid to ovoid 



