8 University of Michigan 



Xo collecting was done at this station in 1918, and the 1914 

 specimens were confused with specimens from other sta- 

 tions, so that only the scanty records of 1913 are available for 

 Lancaster Lake. 



Station XII was a bog area about a mile south-east of Doug- 

 las Lake. Originally more than 250 feet in diameter, the open 

 water has now been reduced to about 30 by 60 feet, with short 

 narrow extensions to the north and south. The water was three 

 or four feet deep in the center, over a very soft peat bed some 

 fifteen feet thick. The vegetation in the open water was rather 

 scanty, consisting of water lilies and some Potamogeton ; and 

 the floating mat at this bog consisted almost entirely of Carcx 

 fiUformis, with only occasional shrubs of Chamaedaphne, and 

 with no Sphagmmi except at the north-west edge. The fauna 

 here was ver}' similar to that at Station IX. 



In addition, one or two collections were made in 1914 at 

 ]\Ionroe and \'incent Lakes, a short distance north of Douglas 

 Lake; but they are not included in the present report, as no 

 field notes were kept and the specimens were placed in vials 

 of alcohol together with specimens from other localities. 



Discussion gi' Spkcies 



Key to tlic Pauiilics of W'atcrbugs of the Douglas Lake Region 



1. Antennae short, concealed in cavities on ventral side of 



head, near eyes ; forms living in water 2 



Antennae exposed, at least as long as head ; littoral forms 



or forms living on surface of water 5 



2. Head overlapping prothorax dorsally ; body flattened above ; 



apical abdominal segments of males asymmetrical Corixidae 



Head inserted into prothorax ; male abdomen symmetrical ; 



form of body variable .• 3 



3. Hind tarsi with two distinct claws ; size larger, length 19 nnn. 



or more 4 



Hind tarsi without two distinct claws (except in Plea, which 

 is less than 3 mm. long) ; size moderate or small, length 

 less than 16 mm.; swim with ventral side upper-.. 



most NOTOXECTID.VE 



