March, 1921] Macro-Fauna of Mirror Lake 155 



preceding collection, the temperature in the spring, though 

 lower than in summer, was more nearly like its preceding, pre- 

 vailing temperature; that is there was less variation in the 

 spring than in the pond. The difference in summer tem- 

 peratures might seem negligible, but in winter the difference 

 might have been of more consequence. No winter temper- 

 atures were taken but the spring water was never frozen and 

 obviously of higher temperature than the shallow pond. Pos- 

 sibly the higher winter temperatures and the smaller variability 

 in temperatures throughout the year explains the matter. 



Asellus communis Say, was not uncommon. More than 

 half were found in the waters of the spring. 



Asellus intermedius Forbes, a smaller species, was far more 

 common. Collections showed three times as many as of the 

 more conspicuous A. Communis. A number of times (April 3, 

 16, May 7, and June 28) mature females were found which 

 bore a brood sac filled with eggs on the ventral side of the body. 



NON-AQUATIC ISOPODA. 



Oniscus asellus Linn. {Oniscidce). This common terrestrial sow 

 bug, is not known to occur in water, though it inhabits moist earth. 

 But one specimen was found in the water of the spring, station 13. 



Armadillidium vulgare (Latreille). {ArmadiUidida). Several spec- 

 imens of this terrestrial pill bug, inactive, rolled up, l^ut alive, were 

 taken from the water, station 13. These, as well as the i^receding, were 

 doubtless there by accident. 



Order Amphipoda. 

 Eucrangonyx gracilis (Smith). This was the one species of 

 the order represented in the pond, and by only a small number 

 of specimens. It was restricted to parts of the small pond, and 

 none were taken later than April. Two out of six specimens 

 carried a large egg mass on the ventral side of the thorax. 



Order Decapoda. 

 Family Potamobiidce. 



Cambarus rusticus Girard. This, one of the commonest 

 species in the region in a variety of situations (Osburn and Wil- 

 liamson, '98) was the only species which could be considered 

 common, and that only on the basis that they were more 

 numerous than the dipnet collecting revealed. Forms so well 

 hidden in the mud as crayfishes, would be easily overlooked. 

 Four out of five individuals sufficiently large for identification 



