456 Wisconsin Academy of Sciences , Arts, and Letters. 
the length and dissimilarity of the setae at the end of the outer. 
“Common in lakes and pools in Yellowstone park.” 
The above is a verbatim copy of the description of Professor 
Forbes. JSTothing was added by Herrick or Schacht. The 
species has not appeared in the collections which have come to 
me, and I regret that I have not had an opportunity to study 
the original collections. The figures of the plate are copies of 
the original figures of Forbes. 
diaptomus spatulocrexatus Pearse. 
1906. Diaptomus spatulocrenatus Pearse, p. 246; figs. 6-9. 
Of moderate size. The first cephalothoracic segment is 
three-fourths the length of the cephalothorax; it has a trans¬ 
verse groove at about its middle The last segment is produced 
posteriorly and armed with two sharp spines on each lateral 
lobe. 
The abdomen of the female is stout. The first segment is 
longer than the remainder of the abdomen. The second seg¬ 
ment is one-sixth as long as the first and one-half as long as 
the third. The furcal rami are one-fourth longer than wide 
and ciliate on the inner margin. 
The antennae are 25-segmented and reach to the end of the 
furca. The right antenna of the male is swollen anterior to 
the geniculating joint. The antepenultimate segment bears a 
hook-shaped process, which is fully half as long as the penulti¬ 
mate segment. 
The first basal segments of the fifth feet of the female are 
armed with strong spines. The lateral hairs of the second 
basal segments are weak. The exopodite consists of two seg¬ 
ments. The second segment is prolonged into a hook, which 
is denticulate on the inner margin; it bears on its outer margin 
three spines, of which the inner is the longest and is distinctly 
plumose. The endopodite exceeds in length the first segment 
of the exopodite, is setose at the tip, and bears two long plu¬ 
mose spines. 
