246 M. A. Ilumbert on Niphargus puteanus, var. Forelii. 



cannot without reserve accept all the combinations of species 

 and genera proposed by this author. Side by side with very 

 interesting observations expounded most ingeniously, M. de 

 Eougemont's memoir contains a certain number of weak 

 points, which prevent our being completely convinced by it. 

 In the first place the discordancy between diiferent parts of 

 the text with respect to the arrangement of the old species 

 imder the different forms observed leaves room for doubt as 

 to the validity of the proposed identifications. Other things 

 also increase our distrust in this respect. Thus fig. 4 on 

 pi. i. represents the last two joints of a foot, reputed to be 

 those of the two anterior pairs of the fourth, fifth, and sixth 

 forms. Now if we compare this figure with that given by 

 Bate and Westwood of Niphargus fontanus^ it will be seen to 

 differ completely. The species of the English authors would 

 be still more difficult to recognize in fig. 3, wdiich represents 

 the second and third forms. 



The figures of the two anterior pairs of feet of the first form 

 are dificrent from those given by Bate and Westwood for 

 Crangonyx suhterraneus ; and it is the more difficult to de- 

 cide whether M. de Rougemont really had this genus under 

 his hands, because he does not tell us whether his specimens 

 presented the entire telson and the last pair of feet with a 

 single unjoin ted ramus, which are important characters serving 

 to distinguish Crangonyx. 



Lastly, my observations on the Niphargi of the Lake of 

 Geneva do not agree with those of M. de Rougemont. 

 Among the animals of this genus communicated to me by 

 M. Forel, some are very small, measuring 2 millims. from 

 the front of the head to the extremity of the last saltatory 

 feet. These individuals ought therefore to take their place 

 under the first form of M. de Rougemont, including all the 

 specimens from 2-4 millims., and consequently correspond to 

 Crangonyx suhterraneus^ Bate. But this is by no means the 

 case. These young individuals undoubtedly present certain 

 differences dependent on age, and consisting in a much smaller 

 number of joints in the antenna?, a smaller quantity of setas 

 upon the different parts of the body, &c. But as to the generic 

 characters properly so called, they are already well marked j 

 and in particular the first two pairs of feet have already the 

 same form as in the adult ^ and the telson is deeply cleft. 



It seems to me, therefore, that whilst we must take account 

 of 1\1. de Rougemont's observations as furnishing a very 

 valuable indication of the metamorphoses which the crus- 

 taceans of the group under consideration may undergo, we 

 cannot yet definitely accept the changes which he proposes in 

 the classification of the forms hitherto observed. I have there- 



