specimen the fourth joint reaches the middle of third 

 antennular joint, and the whole leg is a good deal less 

 robust than in the above-mentioned specimen but agreeing 

 tolerably as to setae ; in a second specimen the fourth joint 

 reaches scarcely the end of second antennular joint, in a 

 third specimen only a little beyond the end of first joint, 

 and in a fourth specimen scarcely to the end of first joint. 

 In the last-named specimen the prehensile legs are evi- 

 dently, but not much, stronger and only a little longer than 

 second pair ; the setae of the fifth joint are proximally less 

 developed, but otherwise both on this and on the major 

 proximal part of the sixth joint distinctly plumose and 

 slightly or scarcely thicker than on second pair ; the 

 seventh joint is somewhat shorter and slightly or scarcely 

 thicker than in second pair, but its setae are nearly spini- 

 form, while they are longer and thinner on second pair. 

 In a fifth specimen there is no other difference between 

 first and second pair of legs than the seventh joint, which 

 in the first pair is conspicuously shorter and with its setae 

 a little stronger than in the second. 



From a station in the « Wood's Hole region » (U. S. 

 Nat. Museum) I have five adult males of T. neglecta, all 

 with the antennular peduncles agreeing completely with 

 those in R. inermis. In one specimen first and second pair 

 of legs are quite similar in all respects, excepting that the 

 seventh joint is a little longer in the first than in the second 

 pair. In a second specimen the fourth joint of first pair of 

 legs reaches the middle of second antennular joint, is 

 somewhat longer and considerably stronger than the 

 second pair, and the specimen is thus almost a typical 

 Thysanoëssa ; the three other males have the development 

 of the prehensile legs intermediate between those of the 

 two other specimens, and an adult female from the same 

 station agrees in the development of first legs completely 

 with the first-named male. And it must be emphasized 

 that the only difference found in any organ between the 

 first-named adult male and a male of R. inermis from 



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