45d 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. Nothing 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. 



DiAPTOiius SPATULOCREXATUS Pearso. 



1906. Diaptomys 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 

 anned 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. 



