﻿NORTH AMERICAN NOTOSTRACA — LINDER 29 



those of Lepidurus, but relatively smaller and pushed laterally, so 

 that the median spines of the two limbs cannot possibly meet each 

 other in the midline. In A. cancrijormis, however, we find an excep- 

 tion. Here, as in the various forms of Lejridurus, I have observed no 

 dwindling of these limbs in large specimens. 



It remains a question whether or not the free end of the duct from 

 the maxillary gland should be regarded as a constituent part of the 

 maxilla. The above-mentioned authors obviously consider it a part 

 of the limb, as do Cannon and Leak (1933). 



It is easily observed that there is no intimate coalescence between 

 the two parts in the Notostraca. In the Conchostraca, too, they are 

 clearly separated from each other. From a theoretical point of view 

 this seems peculiar, and may, of course, be taken as a secondary change. 

 Claus (1873), however, says that the free end grows, in early post- 

 embryonal stages of A. cancriformis, in a place clearly apart from "the 

 masticatory part," and later comes closer to it. He gives his state- 

 ment with some hesitation, but, so far as I can see, no one has since 

 been able to verify or contradict it. 



Grasser (1933) reveals many facts about the development of the 

 excretory organs in early stages of A. cancriformis, but gives no clear 

 information on this point, saying (p. 349): "Der Ausfiihrzapfen . . . 

 erhebt sich zu gleicher Hohe wie die . . . Anlagen des Maxillen — und 

 des ersten Thorakalgliedpaares." Further examination of very young 

 stages seems desirable. 



THE LEGS 



I have not paid much attention to variations of the proportions of 

 the endites of the first pair of legs, because I have found, as did Bar- 

 nard (1929), that individual variation is gi-eat in this respect. Nor 

 have I measured the length or width of the stem, for similar reasons. 

 In other respects the legs of various species are known to be very sim- 

 ilar to each other, though it has been known for a long time that, as a 

 rule, the endites of the first legs are longer in Apus than in Lepidurus. 

 Perhaps we might be able to find some distinguishing characters in 

 the structure of the endopodites of the first pair of legs, which are 

 furnished with setae in some forms and without setae in others, and 

 also, perhaps, in the preepipodites. However, the age variation in 

 these respects is not yet known. Sometimes the epipodites and the 

 exopodites are very much swollen, thus giving the legs a peculiar 

 appearance, but, as the variation shows, this has no taxonomic sig- 

 nificance. 



The number of pairs of legs is seldom given in descriptions of 

 notostracans. They are regarded as extremely difficult to count. 

 I admit the difficulty, though with a pair of fine needles and a good 

 binocular microscope the task is not at all impossible. Some training 



