32 



SIXTEENTH REPORT. 



most typical, large form of the ponds of northern Michigan. Among the 

 secondary species, not counting the pisidia, all of the forms that appeared 

 in the other lagoons were present; they were also in greater numbers than in 

 the smaller lagoons, with the single exception of Lymnaea obrussa which had 

 fallen off in abundance. 



CHART IV.— COMPARISON OF TEMPORARY SWAMPS OF DIFFERENT REGIONS. 



Primary species. 



Lymnaea palustris (Mueller) .... 

 Lymnaea kirtlandiana fLea), var. 



Apleia hypnorum (L.) 



Physa gyrina Say 



Pgyrina, var. hildrethiana (Lea).. 



Physa elliptica Lea 



Physa heterostropha Say 



Secondary species. 



Sphaerium occidentale Prime 



Musculium truncatum (Lindsley) .... 



Musculium partumeium (Say) 



Pisidium roperi Sterki 



Planjrbis parvus Say 



Planorbis parvus walkeri Vanatta 



Planorbis umbilicatellus Gould 



PlaTiorbis exacuous Say 



Segmentina crassilabris Walker 



Lymnaea obrussa peninsulae (Walker) . 

 Lymnaea sp"! 



vA 



A 



i' 



A 



qA 



I 



C 



r' 



Burnt, 

 tam- 

 arack S. 



(14). 



vA 



A 



qC 



I 



A 



C 

 R 

 R 



C 



Rj 



qAd 



vAd 

 Ad 



Id 



McKin- 



non 



Brook 



Flats 



(15). 



vA 



qC 

 qC 



Rj 



I 



C 



Doug- 

 las 

 Lake 

 Region. 



CI 

 qA 



III. TEMPORARY SWAMPS. 



a. Description of Swamps. 



On Grapevine and Hook Points were found remnants of old ponds which 

 had become temporary swamps, mainly thru the deposit of humus by the 

 water plants an(i the surrounding forest trees. These were mostly small 

 and rather barren, and were dry during a large proportion of the summer. 

 Another swamp was reported from near the north shore of North Fish Tail 

 Bay, which appeared from the description to be richer; here Lymnaea palus- 

 tris was said to be quite abundant, but the Avriter was never able to find the 

 place. There were also some larger swamps along the fiats of Bessey Creek, 

 at the other end of the lake, but these appeared very similar to those first 

 mentioned. Lymnaea palustris was also found along the Maple River, the 

 outlet of Douglas Lake. 



There were also many other small hollows thruout the burnt-over, poplar 

 and second growth regions around Douglas Lake, most notably behind the 

 first sand ridge along the south-east shore; this latter might be regarded as 

 a barrier beach formation secondarily increased by wind blown sand. These 

 were similar to the hollows in the sand dunes of Huron County (5), which 

 almost alwaj^s contained little temporary swamps. These places around 

 Douglas Lake maj^ have contained similar swamps before the fires; in fact, 

 Nemopanthus mucronata, a bog plant, was found growing in one of these dry 

 hollows, and a burnt, bleached specimen of Succinea retusa was picked up 

 in another. However, the fire had burnt out the mosses, leaves and humus 

 and had destroyed the shading shrubs and trees, all of which formerly pre- 



