﻿NORTH AMERICAN NOTOSTRACA — LINDER 57 



I suspect that many carciiiologists have had dilRculties trying to 

 identify species of Apus with the aid of Packard's descriptions. 

 Pearse (1912) gives a good example. He had an miusiially large 

 number of specimens from one locality and found a remarkable 

 variation in the number of dorsal spines on the telson, which Packard 

 uses as one of the main characters: "The armature of the telson is 

 somewhat variable; on the dorsal side there is commonly one median 

 spine, but there are often two ; there are usually two lateral spines at 

 the proximal edge of the telson, but there are frequently more" 

 (Pearse, 1912). Here is a mixtui-e of characters from several species. 

 A. lucasanus and A. longicaudatus are described with one median 

 spine, A. aequalis with two, as is one of the specimens of A. newberryi 

 mentioned by Packard. "Lateral spines at the proximal edge of the 

 telson,"probably means the spines around the dorsal sensory setae, of 

 which one on each side is described as large in A. lucasanus. Thus 

 most of Pearse's specimens ought to have agreed with A. lucasanus, 

 but others not. Further, Pearee found the length of the carapace to 

 be "about equal to the portion of the body exposed behind," as in 

 A. aequalis according to Packard; it was obviously on these grounds 

 that he identified his specimens with this species and dismissed the 

 similarities with other species (especially A. lucasanus), which were 

 observed on the telson of most specimens. 



Mackin (1939) says that Packard's thi'ee species are synonyms of 

 LeConte's species; his studies on material from Oklahoma and 

 neighboring States showed that the characters used by Packard are 

 of little value in taxonomies. However, he regards his conclusion as 

 only tentative. 



Packard's descriptions cover a lot of characters, but many of them 

 are considered in only one species, so that comparisons in some re- 

 spects are impossible. Those presented in table 5 are especially 

 stressed by him. (In this table I have, in all eases, given one less 

 ring than Packard, because he obviously counts the telson as a body 

 ring, while I do not.) 



The length of carapace in relation to length of body, and the number 

 of body-rings exposed behind the carapace, vary according to the 

 contraction of the rings, a condition itself higlily variable. These 

 characters are, of course, also influenced by the number of body 

 rings, though in a rather erratic way on account of the variable con- 

 traction of the rings. These characters of Packard's are not simple 

 characters, and generally they are more or less unreliable. 



As for the number of legless rings, the examples in table 6 show 

 how greatly this often varies in specimens from the same locality. 

 The sample from Wyoming (columns a, c) is significant. It contains 

 many more specimens than the others, and it covers the numbers 

 given by Packard as characteristic of three species, A. newberryi 



