4:20 PROCEEDINGS OF THE AMERICAN ACADEMY. 



s. Meropodite of Left Chela. 



'.'. ( !arpopodite of Left Chela. 



10. Propodite of Left Chela. 



1 1. Meropodite of Second Right Leg ; points the same as for meropo- 

 dite of chela, 



12. Meropodite of Second Left Leg. 



frn'prt. 



dac'pd. 



i 



mer'pd. carp'pd. pr'pd. 



Pioi u -. ])'.r>.il surface of Right Chela, dac'pd., dactylopodite; pr'pd., pro- 

 podite ; carp'pd., carpopodite \ mer'pd., meropodite; ba'pd., baaipodite ; CL, length 

 irpopodite ; LP, length of propodite. 



The above measurements are similar to those made for Carcinus 

 maenas by Weldoo ('Jo), but in no case identical with his. lie has, 

 furthermore, expressed ill measurements in terms of total carapace 

 length, bo comparison of our results is impossible. Dr. II. W. Rand* 

 has repeated Weldon's measurements on C. maenas at Wood's Hole. 

 His results, which have not as yet been published, will furnish, in con- 

 on with this study, interesting data for the comparison of Carcinus 

 and ( relasimus. 



The measuring apparatus used consisted of a pair of spring dividers, 

 which could lie adjusted easily and accurately by means of a thumb- 



•v. In measuring, the end of one arm of the dividers was fixed upon 



the point marking one limit of the dimension to be measured and the 



other arm was adjusted by means of the thumb-screw until its point coin- 

 cided with the other limit of the dimension. The dividers were then 

 transferred to a Bteel millimeter scale, above which a pocket lens was SO 



inged as to give a magnification of about twelve diameters, thus en- 

 abling one readily to read Prom the Bcale the distance between the points 

 of the dividers. The Bcale was ruled to fifths of a millimeter, and by 



erminillg whether the fine point Of the arm re-ted in or between 

 and description "f measurements, in manuscript. 



