65f5 MRS. E. W. SEXTON OX 



35. Some Brackisli-water Amphipoda from the mouths of the 

 Weser and the Elbe, and from the Baltic *. By E. W. 

 SextoNj Marine Biological Laboratory, Plymouth f. 



[Received March I, 1912 : Rear] April 23, 1912.] 



(Plates LXXIII. & LXXIV.J) 



Index. 



Pa<?e 



Variation 656 



Systematic: i^ew Species nnder Gammartis 657 



While engaged in determining the Copepoda of the harbour at 

 Bremerhaven, Herr W. Klie met with certain Gammaridea, some 

 of which were not easily referable to known forms. Through tbe 

 intervention of a friend these were submitted to me for examina- 

 tion, and the present paper contains the result, with notes on 

 some other collections of brackish-water Gammarus. There 

 proved to be three species in Herr Klie's collection, one of 

 them {Leptocheirus pilosus Zaddach) already known, the other 

 two apparently new, which I described. But before the descrip- 

 tion was published I received a paper from Dr. Yanhoffen, which 

 contained the description and figures of one of these species 

 under the name of Gorophiuni lacustre. I have therefore in- 

 cluded hei-e only a few notes on this species. Dr. Vanhoffen 

 kindly allowed me to examine his specimens of Amphipoda from 

 the Frisehe Haff, and it is interesting to note that the three 

 species, Leptocheirus pilosus Zadd., Corophium lacustre Vanhoffen, 

 and Gammarus zaddachi, sp. n., are present in both his and Herr 

 Klie's collections. All three appear to flourish equally well in 

 absolutely fresh water as in the brackish water of river estuaries 

 and hai-bour basins. 



The classification of the Amphipoda is rendered exceedingly 

 difficult by the changes or modifications resulting from each 

 successive moult. We know pi-actically nothing yet of the 

 factors influencing the development of any given species, except 

 those of growth and sex. The modifications caused by these two 

 alone are responsible for an excessive multiplication of synonyms; 

 in some cases, Jassa for instance, almost every moult has been 

 given a different specific and sometimes a difljerent generic 

 name by different observers. But in the species of Gammarus 



* [Since this paper was communicated to the Society, nnder the title "Some 

 Amphipoda froni Bremerhaven," the author received some large collections of tlie 

 Gammarus described, which showed remarkable ditferences between those living in 

 salt and in fresh water. These facts have been included in the text, and tbe title 

 has been slightly modified. ]^Ed. P. Z. S. 



+ Communicated by the Rev. T. R. R. Stebbing, M.A., F.R.S., F.Z.S. 



J For explanation of the Plates see p. 665. 



