March, 1921] Macro-Faima of Mirror Lake 153 



Class Pelecypoda. 

 Order Eulamellibranchiata. 



Family Union idee. 



Anodonta grandis Say. This large mussel was an inhabitant 

 of the mud bottom of the large pond, but was not secured or 

 even noticed until the draining of the pond, June, 1920, when 

 two large pails full of specimens, 55 in number, were obtained. 

 No doubt many others were present especially towards the 

 center, so that the species can be easily considered common. 



Family SphceriidcE. 



Musculium transversum (Say). This was the only small 

 bivalve in the pond. At least, in the material identified, all 

 specimens, though none were mature, could quite certainly be 

 referred to this one species. It could be considered common in 

 the small pond (where all specimens were taken) or even 

 abundant for certain areas there, namely stations 12 and 3. 

 None were secured elsewhere. Station 12 was the most favorable 

 locality; the mud was not too deep and glutinous and had a 

 surface layer of the so-called dust fine detritus. This was 

 hardly apparent at station 3, but on the other hand was quite 

 common too, along the east shore. 



Phylum ARTHROPODA. 



Class Crustacea. 

 Subclass Entomostr.\ca. 



All orders having fresh-water forms except Phyllopoda are 

 present in Mirror Lake. Ostracoda are not included in the 

 survey as stated in the introduction. 



Suborder Cladocera. 



Only two species were found in Mirror Lake. In spite of 

 the unfavorable features of the pond, probably more could be 

 expected, since Cladocera thrive in sheltered pools and ponds 

 where food is abundant, live in the littoral region and (Birge 

 '18) "among the weeds and feeding on alg£e, and similar organ- 

 isms." Practically all were taken from the small pond. Possibly 

 other, smaller forms, commoner in open water, were missed. 



Simocephalus serrulatus (Koch), said to be (Birge '18) the 

 most abundant species of the genus was found only at station 3» 

 principally in June. It was not common. 



