March, 1921] Macro- Fauna of Mirror Lake 165- 



The same distribution for these genera, generally speaking, 

 was evident here. 



In the small pond the obstruction of the duckweed covering 

 to convenient surface respiration may have been a factor in the 

 absence of large Dytiscids. But probably more important was 

 the lack of all larger, emergent vegetation, the submerged parts 

 of which are the only places favorable to Dytiscus for egg 

 deposition, (Miall '12). 



In the large pond there was the same lack of emergent 

 vegetation. Absence of practically all vegetation was a factor 

 too, for most beetles naturally thrive best in a certain amount 

 of seclusion afforded by vegetation. 



Very muddy pond bottoms are very poor habitat for 

 Dytiscidse (Sherman '13). He says, in fact: "These beetles 

 prefer for their home bodies of comparatively clear water 

 . . . . where the bottom is at least moderately clear and 

 sandy." This would be optimum for many no doubt, but a 

 small amount of mud would not be a deterrent if other condi- 

 tions were fairly favorable. But in Mirror Lake the mud bot- 

 tom is sufficiently deep and widespread to act as an inhib- 

 iting factor. 



In view of these conditions the collection of Dytiscidae 

 present in the pond was all that could be expected. 



Laccophilus maculosus Say. This was one of the common 

 beetles in the pond, though not nearly as abundant as 

 Tropisternus glaber. It was about equally numerous in all parts 

 of the small pond and in the spring (station 13). 



Laccophilus fasciatus Aube., was not uncommon, but not. 

 more than a third as many specimens were taken as of L. 

 maculosus. Most specimens were from the shallow pool, 

 station 17. 



Desmopachria latissima,* (?). One specimen was obtained 

 at station 11. It should be noted that the species has not 

 been recorded from this region. 



Bidessus affinis Say. This was the one species of the genus, 

 which was even fairly common, considering that probably a 

 relatively smaller number were secured and listed in the table, 

 than of larger beetles. While all specimens were noticed prac- 

 tically on the shoreline, more were found at station 3 than at. 

 the shallower station 11. 



* Identified as probably this species by Mr. C. W. Leng. 



