1895.] into the Measurable Characteristics of Plants, fyc. 361 



The dimensions chosen were: (1) the "frontal breadth" the 

 distance in a straight line between the tips of the extra-orbital teeth 

 of the carapace (from the point A, fig. 1, to the corresponding point 

 on the opposite side) ; and (2) the " right dentary margin" measured 

 in a straight line from the apex of the first to that of the last 

 lateral tooth (from A to B, fig. 1). The "length " of each crab was 

 taken as the length of the carapace, from the tip of the middle inter- 

 orbital tooth to the posterior margin (from C to D, fig. 1). This is, 

 of course, not the total length of the body ; but the curvature and 

 flexibility of the abdomen render an exact determination of the real 

 body length very difficult. 



FIG. 1. 



In order to compare the variability of a dimension in crabs whose 

 carapace is only 7 mm. long with that of the corresponding dimen- 

 sion in adult crabs, whose carapace length is from 40 50 mm. or 

 more, it is evidently necessary to adopt some method of picturing the 

 crabs as of one standard size ; and accordingly the measures obtained 

 have always been expressed in terms of the carapace-length of the 

 crab to which they belong, taken as 1000. The measurements were 

 made by means of a screw, of 1 mm. pitch, carrying the object across 



