NO. 2117. DIAPT0MU8 VIR0INIEN8I8 AND D. TYRELLI— MARSH. 



461 



The description as given above conforms very closely, as in the 

 diagnosis given, Marsh, 1907, to the descriptions given by Poppe and 

 by Lilljeborg in Guerne and Richard 1889. The changes are in 

 minor additions, which are made in order to conform to the more 

 complete knowledge of the species which is fm-nished by the recent 

 collections. 



In most particulars the species seems to be quite constant in its 

 structural characters. The endopodite of the right fifth foot of the 

 male varies in its form and length, but not within 

 wide limits. The endopodite of the left foot is 

 sometimes 1 -segmented and sometimes 2-seg- 

 mented. The spines of the 

 second segment of the exopo- 

 dite of the fifth foot of the fe- 

 male are, in the specimens ex- 

 amined by the author, much 

 more prominent than figured 

 by De Guerne and Richard; 

 the innermost spine is particu- 

 larly long. The variations in 

 the armature of the antepenul- 

 timate segment of the right 

 antenna of the male are par- 

 ticularly interesting. In the 

 original description by Poppe 

 this segment was said to be 

 In the diagnosis of De Guerne and Richard it is 

 said that it is ' 'plane dearmatus, tantum modo modulo minutissimo 

 et vix visibili praeditus." In the specimens from the Pribiloff Islands 

 there was no armature. In those from Yellowstone Park, as shown 

 in figure 6, there was a small hyahne lamella extending back fuUy 

 one-third the length of the segment, and projecting appreciably from 

 the distal end. In the specimens from Alturas as shown in figure 7 

 there is a very minute hyaUne lamella at the distal end of the segment, 

 while in the Tahoe material the armature is entirely absent. 



It appears that the Alaskan material most closely resembles the 

 type described by Poppe. It is generally considered that the anten- 

 nal armature is not subject to variation. If no variability is con- 

 sidered possible, the Yellowstone Park form must certainly be con- 

 sidered a separate species, and possibly the Alturas form another. 

 Considerable interest attaches to just what LiUjeborg had for the 

 description of De Guerne and Richard, the material being collected 

 at "CenterviUe, near Fresno, California," and it is to be hoped that 

 at some time a reexaminaltion may be made of material collected from 

 that locality. 



D. coloradensis was described by Marsh in 1911 from material found 

 in the Rocky Mountains in Colorado; it has since been found in the 



Fig. 6.— DiAPTOMUs ty- 

 EELLi. Terminal seg- 

 ments ANTENNA OF 

 MALE FROM YELLOW- 

 STONE Park, X 445. 



entirely unarmed. 



Fig. 7.— Diaptomus t y - 

 RELLi. Terminal seg- 

 ments antenna of 

 male from Alturas 

 Lake, Idaho, X 445. 



