420 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



8. Meropodite of Left Chela. 



9. Carpopodite of Left Chela. 



10. Propodite of Left Chela. 



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

 dite of chela. 



12. Meropodite of Second Left Leg. 



'ba''pd. 



dae'pd. 



rncr^pd. carp^pd 



pr^pd. 



Figure 2. Dorsal surface of Right Chela, dac'pd., dactylopoilite; pr'piL, pro- 

 podite; wr/j'/)^., carpopodite ; mer'pd., meropodite; ba'pd., hasipodite; C'Z, length 

 of carpopodite ; LP, length of propodite. 



The above measurements are similar to those made for Caicinus 

 maenas by Weldou ('93), but in no case identical with his. He has, 

 furthermore, expressed all measurements in terms of total carapace 

 length, so comparison of our results is impossible. Dr. H. 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- 

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

 and Gelasimus. 



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

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

 screw. 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- 

 ."ided with the other limit of the dimension. The dividers were then 

 transferred to a steel millimeter scale, above which a pocket lens was so 

 arranged as to give a magnification of about twelve diameteis, thus en- 

 abling one readily to read from the scale the distance between the points 

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

 determining whether the fine point of the arm rested in or between 



* Data and description of measurements, in manuscript. 



