Marsh—North American Species of Diaptomus . 409 
Lateral swelling of first abdominal segment 
distinct, sicilis, Ashlandi, oregonensis, 
pallidus, Reighardi, mississippiensis, Lin- 
toni, spatulocrenatus. 
(These species cannot be satisfactorily separ¬ 
ated by the characteristics of the fe¬ 
male, although the limits of size will 
help somewhat.) 
The lateral spines of the abdomen are distinct, 
The exopodite is distinctly three-segmented, 
the endopodite is two-segmented, . Bakeri 
The exopodite is two-segmented, the endopodite 
one-segmented, the second segment of the 
exopodite has three spines, conipedatus , 
clavipes, Tyrelli , leptopus. 
(These cannot be separated by the char¬ 
acteristics of the female.) 
The second segment of the exopodite has two 
spines, siciloides, sanguineus , Birgei, nova- 
mexicanus. 
diaptomus oregonensis Lilljeborg. 
Plate XV, figs. 1, 4, 7. 
1889. Diaptomus oregonensis DeGuerne and Richard, p. 53; 
pi. II, fig. 5; pi. Ill, fig. 8. 
1893. Diaptomus oregonensis Marsh, p. 200; pi. IV, figs. 4, 5. 
1895. Diaptomus oregonensis Marsh, p. 8; pi. VII, fig. 5. 
1895. Diaptomus oregonensis Herrick and Turner, p. 72; pi. 
IV, figs. 7-12; pi. IX, fig. 3. 
1897. Diaptomus oregonensis Schacht, p. 151; pi. XXIX, figs. 
1 and 2. 
1906. Diaptomus pygmaeus Pearse, p. 244; figs. 1, 2 and 3. 
Of medium size. Cephalothorax widest at the middle. The 
first segment of the cephalothorax exceeds in length the three 
following segments. The last segment is slightly produced 
laterally and armed with two minute spines. 
The first segment of the female abdomen equals in length 
the rest of the abdomen. It is slightly expanded laterally, 
and sometimes bears two very minute lateral spines; these, 
however, are not always present. The second segment is shor* - 
than the third, and the third shorter than the furcal rami. 
The length of the furcal rami is twice their width; they are 
finely ciliate on the inner margin. 
