122 Illinois State Lahoratorij of Natural History. 



right somewhat the longer. First two thoracic seg- 

 ments equal, together about half as long as entire 

 thorax ; last segment armed with two small spines. 

 Second segment of outer ramus very broad, especially 

 at the base. Inner ramus hairy on outer margin and 

 at tip, which is armed with two rather long slender 

 spines. Antennae reaching beyond furca. 



m ississippiensis. 



Diaptomus sicilis Forbes. (PI. XXL, Fig. 1-3.) 



Diaptomus sicilis, Forbes, '82a, p. 645, PL VIII., Fig. 9, 20. 

 Diaptomus pallidas var. sicilis, Herrick, '81, p. 142, PI. Q, Fig. 18. 

 Diaptomus sicilis, de Guerne et Richard, '89b, p. 23, Fig. 13, 14; P]. 



II., Fig. 13. 

 Diaptomus sicilis. Forbes, '90, p. 702, PI. I.. Fig. 6. 

 Diaptomus sicilis, Marsh, '93, p. 197, PI. III., Fig. 8, 10. 



Body slender, widest in front of the middle ; suture between 

 head and thorax distinct. Last two thoracic segments con- 

 fluent ; the last one produced laterodorsally and armed on each 

 side with one or two small spines ; (in the male unarmed.) 

 Abdomen long and narrow, especially in the male, in which 

 the first segment is the longest and slightly the broadest. In 

 the female (PI. XXL, Fig. 3) this segment is fully as long as 

 the remainder of the abdomen, dilated, and armed on each 

 side with a spine ; last three segments subequal. Furcal 

 rami fully twice as long as broad and hairy within. 



Antennae 25-segmented, reaching well beyond the tips of 

 the furcal rami. Male geniculate antenna moderately swollen 

 beyond the twelfth segment; first two segments without 

 special armature ; antepenultimate segment armed with nar- 

 row spine-like process with swollen apex, reaching to the 

 middle of the penultimate segment; segments 19, 20, and 

 21 confluent, as are also 22 and 23. 



Fifth pair of legs in the male (PI. XXL, Fig. 1) rather 

 long and slender. First basal segment of the right foot with 

 a large tubercle on the posterior surface near the outer mar- 

 gin, bearing a minute blunt spine. Second basal segment 

 subquadrate, about one and a half times as long as broad. 

 At the beginning of the distal third of its outer margin, is a 



