Feb., 1920] The Protozoa of Mirror Lake 117 



Pleuronema chrysalis (Ehrenberg). 



This species was abundant throughout the period of study- 

 in all collections from Stations G and H. It multiplied rapidly 

 in a standing culture. In the fall and again late in March it was 

 abundant among floating algae at Station C and in sediment 

 at Station F. 



Length 70-102^. 



Cyclidium glaucoma Ehrenberg. 



This protozoan was abundant in November among alga- 

 covered poplar roots (Station D), in January, in algae from the 

 bowl of the spring (Station J), and in February, on algae 

 growing on the rocks at the point where the spring water enters 

 the larger pond (Station E). In all these places the water was 

 clear and fresh. The movements of the animal which are very 

 quick and jerky, recall those of water striders. 



Length 24^. 



Order Heterotrichida. 



Family Plagiotomidce. 



Spirostomum ambiguum Ehrenberg. 



This very large protozoan was common in the black sediment 

 at Station B ; it was taken here only during October and Novem- 

 ber. Late in March, several individuals were found in sediment 

 at Station L. 



Length 296-1280^; breadth 30-144m. 



Metopus sigmoides Claparede and Lachmann. 



This species was common in the fine black sediment at 

 Station M, at which collections were made only in March. A 

 few individuals were taken among Oedogonium filaments 

 (Station H) about the same time. 



Length 90^. 



Family BursaridcE. 



Busaria truncatella Miiller. 



One individual was taken in March in algae from submerged 

 posts (Stations I and I'). 



Length 224^. 



