Marsh — North American Species of Diaptomus. 441 



DIAPTOMUS TYBELLI PoppC. 



Plate XIX, tigs. 2, 3, 8. 



1888. Diaptomus Tyrelli Poppe, p. 159. 



1889. Diaptomus Tyrelli DeGuerne aud Richard, p. 39 ; pi. I, 



figs. 17, 18 ; pi. IV, fig. 26. 

 1895. Diaptomus Tyrelli Herrick and Turner, p. 76 ; pi. X, 



fig. 9.- 

 1897. Diaptomus Tyrelli Schacht, p. 176. 



Of medium size. The suture of the first cephalothoracic 

 segment is rather distinct. The first segment is considerably 

 less in leug-th than the thre^ following. The last cephalotho- 

 racic segment is expanded into large lateral processes, and is 

 armed with rather large lateral spines. 



The first segment of the female abdomen equals in length 

 the rest of the abdomen. It is broad, dilated in front, and 

 moderately dilated laterally. It bears prominent lateral proc- 

 esses, which are tipped with acute spines. The second seg- 

 ment is shorter than the third, and the tAvo together are some- 

 what longer than the furca. The furcal rami are stout and 

 ciliate on both the inner and the outer margins. 



The antennae are 25-seginented and reach about to the end 

 of the furca. The antepenultimate segment of the right male 

 antenna is without any special appendage. 



The fifth feet of the female are slender. The spines of the 

 first basal segments are small and acute. The lateral hair of 

 the second basal segment is of moderate length. The first seg- 

 ment of the exopodite is more than twice as long as wide. The 

 second segment is long and slender, exceeding in length the 

 first segment. The hook is slightly curved and denticulate on 

 the inner margin. It is armed with three spines of which the 

 inner is the longest. The two inner spines represent the third 

 segment. The endopodite is long and slender, exceeding in 

 length the first segment of the exopodite. It is setose at the 

 tip, and armed with two long terminal spines which are insert- 

 ed well back froiri the end of tlie endopodite. 



