YERKES. — VARIATION IN THE FIDDLER CRAB. 



429 



Polygon No. 4R. 



Polygon No. 4L. 



4. Left margin. Polygons No. 4R and 4L. Compare also No. 4R 

 with 3L. The three dimensions thus far considered are the most valu- 

 able for place-mode determinations because they are expressive of the 

 form of the carapace and may be measured with ease and accuracy. As 

 given in Table I., the modal classes of the Lefts, — in two instances, — 

 the frontal breadth and right margin, are below those of the Rights; in 

 both of these cases there is considerable difference in the means. 



