Marsh—North American Species of Biaptomus. 435 
ceived. It was too late to secure material to verify 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 
he well founded. It falls into the tenuicaudatus group, and 
is closely related to B. 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 indistinctly 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 B. shoshone, it seems best to recognize the species for the 
present. 
diaptomus bibgei Marsh. 
Plate XVIII, figs. 6, 8. Plate XIX, figs. 1, 6. f 
1894. Biaptomus Birgei Marsh, p. 16; pi. I, figs. 4-6. 
1895. Biaptomus Birqei Herrick and Turner, p. 79; pi. 
XLVII, fig S : 4-6. 
1897. Biaptomus Birgei Schacht, p. 172. 
1903. Biaptomus Birgei Juday, p. 123. 
Of moderate size. The first segment of the ceplialothorax 
is nearly equal in length to the three following. The last cepha¬ 
lothoracic segment is armed laterally with two minute spines. 
The first segment 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- 
