﻿168 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lOo 



segment, a number of hairs on distal end and a distinct, thougli short, 

 spine present on mesial surface ; (5) terminal end of endopodite armed 

 with some minute setae. But the other characters of the male fifth 

 pair of legs agree with those given by Kief er. 



From this comparison it will be seen that the specimens from Erh 

 Hai have many points in the structure of the abdomen and fifth 

 pair of rudimentary legs to justify putting them in a separate species, 

 though their general form shows close affinity to T. hebereri; hence 

 the name hebereroides. 



Genus ARCTODIAPTOMUS Kiefer 



Pakabctodiaptomus, new subgenus 

 ARCTODIAPTOMUS (PARARCTODIAPTOMUS) HSICHOWENSIS, new species 



Figure 21 



The second new form of diaptomid was collected in the same plank- 

 ton hauls as the foregoing species. It is nearly as abundant in the 

 lake as Tropodiaptomus hebereroides. Its smaller size, both male and 

 female, helps to distinguish it from the other species of diaptomid 

 in the same plankton sample. 



Diagnosis. — The subgenus Pararctodiaptonmis belongs to Arctodi- 

 aptomus but is distinguishable as a separate group by the smallness 

 of the pincerlike structure on the distal end of the left exopodite of 

 the fifth rudimentary leg of the male. It is separable from Arctodi- 

 aptomus s. str. by the absence of spine from the fourteenth joint of 

 the right first antenna (gi^asping antenna) of the male. In contrast 

 to Rhahdodiaptortius., the fourth and fifth thoracic segments are not 

 fused, and the antepenultimate joint of the grasping antenna has no 

 spine. The presence of spines on the thirteenth and fifteenth joints 

 of the same antenna, that on the thirteenth being very large, differen- 

 tiates this subgenus from Haplodiaptomus. Unlike Stenodiaptorrms 

 the distal half of second joint of fifth male right exopodite is not 

 reduced in diameter. 



Tj^pe species : ArctodiaptomMs {Pararctodiaptomus) hsichowensis. 



Description. — Female: Anterior body region calanoid; first tho- 

 racic segment broadest, carapace only slightly shorter than thoracic 

 segments (actual ratio of their lengths, 11 : 13), both length and width 

 of thoracic segments decreasing posteriorly from first to fifth, fifth 

 segment not fused with fourth, with posterolaterally extended wings, 

 tip of wing armed with sharp hyaline spine, posterior aspect of fifth 

 segment with hyaline spine near spine on tip of wing, two sides sub- 

 symmetrical. Abdomen (or posterior body region) consisting of three 

 segments: genital segment larger, longer than total lengths of rest 



