M. A. Humbert on Niphargus puteamis, var. Forelil. 247 



fore provisionally retained the genus NipharguSy modifying it 

 and completing its diagnosis. 



In the state of confusion which prevails at present among 

 the species of this genus their determination is difficult, 

 whether we accept the arrangement of Schiodte and Spence 

 Bate, or, like I)e Rougemont, only regard the forms de- 

 scribed as representing the successive phases of a single type. 



The Niphargus of the Lake of Geneva, and that which I 

 have found in a well in the environs of Geneva, although 

 very different in size and presenting some slight differences 

 of organization, did not seem to me to need separation other- 

 wise than as varieties. This point once settled, I had to 

 inquire whether the species was new, or whether it fell under 

 one of those which were already described. It seemed to me 

 to be quite distinct from N. aquilex^ fontanus^ and stygiuSj 

 and, although more nearly allied to N. Kochianus^ could not 

 be confounded with it. 



As to the six forms of M. de Rougemont, there is not one 

 to which I could with any probability or confidence refer those 

 which I have before me. The figure given by that author 

 representing the last two joints of a foot of the fourth, fifth, 

 and sixth forms, resembles these same parts in my specimens ; 

 but as I have already stated, that figure is not in accordance 

 with some of those of the authors quoted. 



It will be always difficult to arrive at a decided opinion with 

 regard to the Gammarus puteanus of Koch, which is described 

 and figured in a very unsatisfactory manner. Nevertheless 

 the name given by Koch has been in a manner fixed in science 

 by the memoirs of Caspary and Hosius, who have given very 

 good figures of the species. Thus it seems to me that, until the 

 contrary is proved, we may regard the name of Qammarus 

 jputeanus as applying to the species which has been described 

 and figured by these two authors. Now it is to this that my 

 two varieties seem to approximate most closely, notwith- 

 standing slight differences in the proportion of the propoda of 

 the first two pairs of feet. I have consequently adopted for 

 the species the name of Niphargus puteanus^ Koch, distin- 

 guishing each of the two local varieties, however, by a special 

 name : the form from the Lake of Geneva is Niphargus pute- 

 anus J var. Forelii; and that found in a well at Onex, N.pute- 

 anuSj var. 07iesiensts. I have completely described only the 

 former, and contented myself with indicating the differences 

 which exist between it and the second form by placing in a 

 tabular form those whicli seemed to me well marked. A 

 detailed comparison with the type of the preceding authors is 

 impossible, because the latter has not been described with 

 sufficient exactitude. 



