﻿52 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



is a large number of spines of varying sizes (2-3 spines in L. lemmoni) . 



Even the place of the nuchal organ is as m Z. couesii. All characters 



considered, the specimens are quite typical representatives of this 



species. 



Genus APUS Schaeffer 



Apus Schaeffer, 1756, p. 131.— Gurney, 1923, p. 497.— Barnard, 1929, p. 229.> 



The prkicipal characters of the genus are, in my opinion, the 

 absence of a supra-anal plate on the telson (p. 26), the relatively 

 large number of body-rings, 30-^4 as against 25-34 in Lepidurus 

 (p. 42), and the reduction of the second maxillae in full-grown speci- 

 mens (p. 28). 



Even within these limits, however, the genus presents a unit that 

 is not quite homogenous or well distinguished from the genus Lepi- 

 durus, because one species, A. cancriformis , is in several respects sug- 

 gestive of the latter genus. 



Absence of a supra-anal plate seems to be characteristic of all 

 species except A. cancriformis, where we may find something rather 

 sunilar to such a plate (fig. 8). It is very short, but we can only 

 assume that it is essentially the same structure as the plate in Lepi- 

 durus, so that A. cancriformis may be regarded as an intermediate 

 stage, in this respect, between Lepidurus and the remaining species 

 of Apus. 



In the reduction of the second maxillae, the same species forms an 

 exception. I have found it to have, in full-grown specimens, just as 

 well developed maxillae as in any species of Lepidurus. 



It has very few body-rings as compared with almost aU the other 

 species of the genus that I have examined. There are a minimum of 

 30, and, generally, a maximmn of 34. In only one sample of A. 

 cancriformis have I found more, 35 in a female and 35 or 37 in the 

 males (U.S.N.M. No. 58211, from Nanking, China). I have observed 

 a similarly small number of rings in A. sudanicus from South Africa, 

 identified by Barnard (U.S.N.M. No. 75749). The male in this 

 sample has 32, the two females 33 and 33+i body-rings. All the other 

 species of Apus have a larger number of body-rings. A. longicaudatus 

 comes nearest with 34-t-i-44 rings (see table 4); however, I am fully 

 aware that in many forms we know too little of the number to be able 

 to make definite groupings of the species according to this character. 

 Still, it may be considered significant that A. cancriformis, which comes 

 close to Lepidurus in the structure of the telson and the second 

 maxillae, also has a similar total number of body-rings. This is a 

 further indication that the species is a sort of connecting link between 

 the two genera. 



1 1 fully agree with Qurney and Barnard that the name of Triops Schrank, 1803, pp. 180, 251 (sometimes 

 spelled Triopes or Thriops), ought to be rejected. 



