J!I2 



Variation in " Btipagums Prideaiixi'" 



2. The length of the right chela measured t'rom its lower articulation with 

 the carpopodite, to the furthest point of the fixed blade of the scissors. Fig. 1, CD. 



3. The length of the carapace along the median line. 



These nicasurements werc takeii with a pair of dividors provided with a screw 

 tine adjustment and an ivory scale diviiled into ^ niillinietres, they are believed to 

 be aceurate to -^ of a miliimetre. 



From Me;isurements No. 1 and No. 2 an index called ihe chela index was 

 dcdnced, which is intended to represent the proportion wliich tlie claw bcars to 

 the wholc length of the chela. 



The chela index = 



Meiisurement No. 2 — Measurement No. 1 

 Measuiement No. 2 



About two thousand individuals were measured, which were separated into two 

 main groups : 



I. Shalloiu water forms, fiom a depth of 35 metres or under; 



II. Deep water /onus, from a depth of over 85 metres. 



Owing to the great ditference in size between the sexes each of these groups 

 was again subdivided into male and femalc. Thus finally we have to deal with 

 four sets with about fivc hundred individuals in each. 



IJ. 



Compariiiun between deep water forins and shallow water furnis an regards each 

 measurement and the chela index taken separatehj. The deep water males are in 

 each case compared with llie shallow water males and the deep water feraales with 

 the shallow water fcmales. 



TABLK I. 

 Measurement No. 1. (/'. 



This measurement is greater in the shallow water forms by an amount exactly 

 five times as great as its probable error, and therefore almost certainiy significant. 



