Marsh — North American Species of Diaptomus. 435 



ceived. It was too late to secure material to vorify the descrip- 

 tion, or to prepare figures. I have therefore taken his descrip- 

 tion verbatim. Although his description of the female is 

 somewhat incomplete, it would appear that the species may 

 be well founded. It falls into the tenuicaudatus group, and 

 is closely related to D. shoshone Forbes. It is very possible 

 that a careful examination of a large number of specimens 

 will show that it is only a variety of this species. The points 

 of marked difference, besides that of size, are the greater 

 length of the appendage of the antepenultimate segment of 

 the right male antenna, the form of the terminal segment of 

 the left exopodite of the male fifth foot, and the two-segment- 

 ed endopodite of the female fifth foot. The endopodite of the 

 female fifth feet is only indistiii-Ctly two-segmented in sho- 

 shone, and this condition might be easily overlooked in the ex- 

 amination of a few individuals. The appendage of the an- 

 tepenultimate segment of the right male antenna, too, may be 

 somewhat variable. Inasmuch as Pearse gives no figure of 

 the female abdomen, we are left in doubt in regard to its 

 form. While it is very possible that we have here a variety 

 of D. shoshone J it seems best to recognize the species for the 

 present. 



DIAPTOMUS BiKGEi Marsh. 



Plate XVIII, figs. 6, 8. Plate XIX, figs. 1, 6. 



1894. Diaptomus Birgei Marsh, p. 16; pi. I, figs. 4-6. 



1895. Diaptomus Birgei Herrick and Turner, p. 79 ; pi. 



XLVII, figs. 4-6. 

 1897. Diaptomus Birgei Schacht, p. 172. 

 1903. Diaptomus Birgei Juday, p. 123. 



Of moderate size. The first segment of the cephalothorax 

 is nearly equal in length to the three following. The last cepha- 

 lothoracic segment is armed laterally with two minute spines. 



The first seginent of the female abdomen is as long as the re- 

 mainder of the abdomen and the furca. It is much dilated on 

 the ventral surface, and moderately dilated laterally. The lat- 



