32 



PROCEEDINGS OF THE ACADEMY OP 



[Jan., 



Fig. 7— Heights— Upper line, 225 Michigan and 124 Isle Royale. Lower line 



225 Michigan. 



The 170 specimens of the major form vary in height from 15.25 to 

 24.25, with an average of 19.06 mm. 



The major mode is at 17, with well-marked minor modes at 18, 20 

 and 20.75. 



In width (fig. 5) the series vary from 24.75 to 34.25 mm., with an 

 average of 29.31. The major mode is at 29, with conspicuous minor 

 modes at 25, 26.75, 28 and 30.5. 



/Z 1 .'3 ± ,y ± /J" ± 16 ■£ qnv-^. 



Fig. 8 — Heights — 55 Michigan, minor form. 



The 55 specimens of the minor form vary from 12 to 17 mm. in 

 height, with an average of 14.67. The curve is practically trimodal, 

 with the modes at 13.75, 14.75 and 15.75. 



In width (fig. 5) this series ranges from 18.75 to 24.5 mm., with an 

 average of 22.3. The curve is multimodal, with nearly equal modes 

 at 19.75, 20.5, 22, 23, 23.75 and 24, indicating a higher degree 

 of variability than in the major form. 



