﻿NORTH AMERICAN NOTOSTRACA — LINDER 31 



It is often stressed that, in relation to the body, the carapace is 

 larger than in Apus, thus leaving a smaller number of bod3'--rings 

 uncovered. This certainly is true of most species, but in L. bilobatus 

 and the new species the number of such rings is quite as great as the 

 usual number in Apus. 



In the generic diagnosis we should include the numbers of body- 

 rings and of pairs of legs. In these respects, there are two groups 

 of species m the genus. L. apus, L. arcticus, L. couesii, L. kirkii, 

 L. packardi, and L. viridis are characterized by fewer rings and legs: 

 9.5-13 abdominal leg-bearing body-rings, 25-29 body-rings in 

 all, and 35-46 pairs of legs. The second group consists of L. bilobatus 

 and the new species and variety of this genus. Here we find 14.5-18 

 abdominal leg-bearing body-rings, 30-34 body-rings in all, and 60-71 

 pairs of legs. These differences may be expressed by saying that the 

 leg-bearing part of the abdomen is more developed in the last group 

 than in that first mentioned. 



This is not the place to give a world-wide enumeration of the species 

 of Lepidurus described by various authors, or to give an account of 

 their synonjmiy, but, as far as I can see, so many of these are synonjrms 

 only that I can maintain that I have examined specimens of all species 

 except L. patagonicus, and that the above considerations apply to all 

 species of the genus I have examined. 



Sidorov (1927) refers to his paper (1924) in which he erects a new 

 genus, Bilobus, for L. bilobatus. This genus is founded on minor 

 characters, some of which are not even fit for specific demarcation 

 (bilobation of the supra-anal plate, for example, is observed in many 

 species). The 1924 paper, written in Russian, was not available for 

 my inspection. 



As for other characters, readers are referred to the descriptions in 

 this paper. 



About the distribution, I agree with Barnard (1929, p. 228): 

 "Lepidurus is confined to the more boreal portions of the Palaearctic 

 and Nearctic regions, New Zealand, Tasmania, the southwestern and 

 southeastern coastal belts of Australia, and Patagonia. In regions 

 of a hotter and more arid climate, subject to periodical droughts, it 

 is replaced by Apus. The hmits of distribution of the two genera 

 overlap in places, but in general the above marked separation holds 

 good." 



In North America, members of the genus occur in the Arctic and 

 in the western part of the continent: L. arcticus in northern Canada, 

 Greenland, and Alaska; and the other species in Alberta and Sas- 

 katchewan, in Canada; and in Washington, Oregon, Montana, Idaho, 

 North Dakota, California, Utah, Nevada, Arizona, and Colorado, in 

 the United States. East of the Mississippi, Lepidurus is not recorded 

 and east of the Alissouri only once (Max, N. Dak.). It is, of course, 



