138 College of Forestry 



was examined only incidentally and the number of units is 

 too small for a conservative estimate of the population, though 

 it is believed that the figures here given are fairly reliable. 



South Shore of the Lake East of Norcross Point. The 



territory bordering the shore east of Norcross Point is strik- 

 ingly bouldery, the rocky bottom extending nearly or quite to 

 the 6- foot contour. The shore was studied in detail for a dis- 

 tance of 3,700 feet eastward from the point and for a width 

 of 200 feet, the territory embracing a sf[uare area of 740,000 

 feet. Ninety-four unit boulders were studied, the animal life 

 on which totalled 290 mollusks and 1,082 associated animals, 

 a total population of 1,372 (Table No. 35). The average per 

 boulder was 3.08 mollusks and 11.51 associated animals, a 

 total average population of 14.59. This unit indicates a popu- 

 lation of 14,675,786 mollusks and 54,754,716 associated ani- 

 mals for this bouldery shore area or a total population of 

 69,430,502.* The average number of animals per boulder unit 

 of the same size is smaller than that of the boulder area in 

 Lower South Bay, the former being 1.85 and the latter 4.09 

 for mollusks. The difference is not so great for associated 

 animals, the ratios being 6.9 and 8.37 respectively. 



The table of areas examined (No. 35) shows that Gonio- 

 basis and Amnicola are the characteristic genera. Physa, 

 Lymncea stagnalis lilliancc, and Planorbis binneyi are also 

 notably abundant. Among the associated animals the caddis- 

 fly larva Helicopsyche is most characteristic. Chironomid 

 larvae lead in number of individuals followed by worms and 

 Hyalella. The minute ostracods are most numerous next to 

 the dipterous larvae but their small size renders them relatively 

 insignificant. The small number of mollusks (21. i percent) 

 as compared with the large number of associated animals (78.8 

 percent) is notable. 



Deep Water Habitats. There is one area studied (|uan- 

 titatively still to be considered, the territory outside the 6- foot 



* The computation is as follows : 740,000 square feet X 144 square 

 inches = 106,560,000 square inches, -^ 22.4 (average size of boulder unit 

 area) = 4,757,143 units, X 3.085 mollusks = 14,675,786 mollusks, and 

 X 11.510 = 54,754,716 associated animals. 



