Feb., 1920] The Protozoa of Mirror Lake 101 



distinctly granular nucleus, others with a half dozen or more 

 ellipsoidal nuclei. The extended individual, (PI. II, Fig. 1), 

 measured 360/x. 



In February several smaller animals of the same species 

 were taken at the entrance of the spring into the larger pond 

 (Station E). In these the pseudopodia were very numerous, 

 long, and anastomosing, and the contractile vacuole could 

 easily be seen. 



Length of individual shown in Plate II, Fig. 2, is 144ju. 



Family Arcellidce. 

 Arcella vulgaris Ehrenberg. 



This species was taken throughout the period of study 

 but only in occasional collections of alga-covered poplar roots 

 from Station D. It was rare in new material, but increased 

 rapidly in standing cultures. The individuals varied greatly 

 in size and were light brown in color. 



Breadth of shell 48-133)u; diameter of mouth 25-59^- 



Difflugia globulosa Dujardin. 



This species occurred throughout the period of study at a 

 variety of stations in the lake. It was abundant in sediment 

 from Stations F and K, among algae at Stations I and I', and on 

 sediment from Station B. The animal multiplied rapidly in 

 a standing culture. 



Length 72-144ju; breadth 80/x. 



Difflugia lobostoma Leidy. 



This form was common only in December among algae 

 taken at the point where the spring water enters the larger pond 

 (Station E). It was infrequent in November and January 

 among the dead Oedogoniiim (Station H), among floating algae 

 from Station C, and in sediment and algae from Stations K 

 and L. 



Length 54-82ju. 



Difflugia acuminata Ehrenberg. 



One individual was taken in February among algae scraped 

 from a submerged stone at Station G. Its length was 219^ and 

 the diameter of the mouth was 48)U. A much smaller specimen 

 was found among dead Oedogonium (Station H), in March. 



Length 72/i. 



