82 Mr. A. 0. Walker on Pherusa fucicola, Leach. 



Mr. Pocock (' Annals,' June 1891, p. 533) says:—" All that 

 those who hold to" Rule 11 " can expect is that an author 

 ghould point out such characters as are believed in his day to 

 he essential." He then quotes my article, in which I state 

 that Thernsa fucicola disagrees in almost every particular with 

 Leach's definition both of its genus and subdivision, and says 

 that this is substantially true of the later description in the 

 Linn. Trans , but not of the original description in the Edinb. 

 Encycl. But, in the first place, the only important differ- 

 ence between the two descriptions is that the latter contains 

 the correct addition that the tail is not " fasciculato-spinosa " 

 and the incorrect one that there is no secondary appendage to 

 the upper antenna?. If we are to accept this view, then we 

 shall come to the reductio ad absurdum that the more indefinite 

 our descriptions are the better, and that if Leach had simply 

 described Pherusa as an " animal having legs " his position 

 would have been unassailable [ In the second place, as will 

 be seen by reference to p. 533, Leach went altogether wrong 

 in his classification of Pherusa. His division a, including 

 Melita and Mfera, is obviously founded on the characters of 

 the males, in which the second gnathopods are very much 

 larger than the first, while in the females the difference is 

 trifling. And this is 'precisely the case loith Gammarella 

 hrevicaudata; so that had Leach known the male he wouhl 

 certainly have ]daced his Pherusa in division a, and not in c \ 

 Can it then be said that Leach " pointed out such characters 

 as " he " believed to be essential " ? "What carcinologist^ 

 with only the Edinb. Encycl. description to go upon, would 

 have dreamt of referring Gammarella to Pherusa? Much 

 rather would he have thought it referred to one of the large 

 family of Lysianassina;, in which the first and second gnatho- 

 pods are nearly always " filiform " (as Leach would have 

 called them) in both sexes, but whose aflSnities arc suffi- 

 ciently remote from Pherusa [Gammarella). 



As regards the retention of Bate's genus Pherusa, 18G2, I 

 must unreservedly admit that ^Ir. Pocock is right and I am 

 wrong. In my anxiety to avoid encumbering our list with 

 another genus, and also in the hope tiiat it might be found 

 possible to absorb the present species of Pherusa (of which 

 there appear from the ' Challenger' Bibliography to be eight) 

 into other existing genera, I did not consider the possibility 

 of other authors between 1815 and 18G2 having used the 

 name. As j\lr. Pocock says, and as Dr. Norman had pre- 

 viously pointed out to me, this has been done in more than 



