﻿NORTH AMERICAN NOTOSTRACA — LINDER 3 



only rarely, as in the Anostraca and in the Conchostraca, and if it 

 should happen to occur in a particular sample, the fact would prob- 

 ably be readily revealed when all characters are considered. I have 

 not found any indications of mixed populations in this sense in the 

 samples I have examined, nor can I find any definite reference to 

 it in the literature, with the exception that Lundblad (1920) noted 

 that species of different genera sometimes have been found in the 

 same pool. In these cases no intermediate forms are reported. 



So far, I have considered only specific characters. Sidorov (1927) 

 and Gauthier (1934) are convinced that there are geographical sub- 

 species within Apus cancriformis of the Old World. I do not deny 

 the possibility that there may be such taxonomic units in some 

 North American species, most likely among the forms of Apus. 

 Among the anostracans, which have similar habits, I have found 

 some indications of geographical subspeciation in forms of the 

 genera Branchipus and Tanymastix of the Old World. Smirnov (1931) 

 seems to be of similar opinion with regard to some conchostracans. 



However, I do not find it possible to separate geographical units 

 out of the material to which I have had access. In my opinion the 

 appropriate way of doing this would be to investigate thoroughly 

 some limited areas, and to follow this with a comparison of samples 

 from interspersed districts. The possible existence of chnes (Huxley, 

 1942, and Margalef, 1948) might also be traced in this way. 



During my work it appeared that a species from Asia and Europe, 

 Lepidurus macrurus, is a synonym of the American species L. couesii. 

 Further, I found that South American forms of Apus are the same 

 species as the North American Apus longicaudatus. This may be 

 significant. It is worth noting that no one since the days of Packard 

 (1883) and Simon (1886) has tried to compare species from all over 

 the world, and, with our present knowledge of the great latitude in 

 variation of many characters, it does not seem at all improbable 

 that additional species from different continents will be found 

 synonymous. 



The present tendency to reduce the number of species in the 

 Notostraca (see Gurney, 1924, and Barnard, 1929) is, I think, sound, 

 and is well supported by our present knowledge of variation. This 

 paper follows the same line. 



In the following pages I have tried to analyze, with the help of 

 material from all continents, the commonly used taxonomic charac- 

 ters and, also, a character which has been very much neglected, the 

 number of body-rings of different kinds. This character has proved 

 quite useful. One of the results is a new grouping of the species of 

 Lepidurus into what seems to be two natural groups; another, that 

 lower taxonomic units begin to be revealed among parthenogenetic 



