288 Birge — Notes on Cladocera. 



Cladocera,* M. Jules Richard concludes that less than one-half 

 of the species found in Nor-th America are peculiar to that coun- 

 try, and that careful revision will reduce this proportion. He 

 gives a list of species found here, using as authority, apparently, 

 Herrick's list in the Minnesota Geological Report for 1884. 

 This list contains a large number of species both from my 

 paper of 1878 and from Herrick's own work, which are unques- 

 tionably synonyms of European species. The real relation of 

 the fauna of the north central states of this country can not 

 differ very greatly from the proportions as given in this paper. 



In his statement of conclusions to be drawn from the ob- 

 served facts of the geographical distribution of the Cladocera, 

 M. Richard expresses himself with great caution. Neverthe- 

 less, I think that he has gone somewhat further than the facts 

 warrant in even the following cautious opinion: 



"Dans plusieurs parties du monde, on trouve des types spe- 

 ciaux, le plus souvent en tres petit nombre, et noyes en milieu 

 d'une foule de formes tres repandus. Nous avons en Europe: 

 Limnosida, Anchistropus, Comiger ; en Afrique: Guernella, 

 Grimaldina; dans l'Amerique du Nord: Pseudosida; en Austra- 

 lie: Latonopsis." 



My own observations show that two of the seven peculiar 

 genera enumerated are found in Wisconsin. Anchistropus and 

 Latonopsis are represented here by species very close to the 

 Australian and European forms respectively. I have little doubt 

 that Limnosida will be found by careful study of our northern 

 lakes. If not, it will be the only European species of Sididse 

 which is not found in this country. Comiger is a salt water form 

 of the Polyphemidse from southern Russia. No studies have been 

 made in this country in corresponding latitudes which will 

 warrant the assertion that the genus is not found here, and the 

 same statement may be made regarding the other genera men- 

 tioned by M. Richard. 



The facts so far as known to me justify the expectation that 

 all genera of Cladocera are intercontinental in their distribu- 



*Sur la Distribution Geographique des Cladoceres. J. Richard. Re- 

 ceived October, 1893, as a separate reprint from a Russian journal, but 

 without name of journal or date of publication. 



