North American Species of Diaptomus. 121 



hairy, armed with two small spines. Antennae reach- 

 ing slightly beyond end of furcal rami. siciloides. 



38 (37). Second abdominal segment slightly shorter or at 



least not longer than the third. 



39 (42). Furca longer than third abdominal segment. 



40 (41). First abdominal segment nearly as long as remain- 



der of abdomen ; dilated laterally, armed with one 

 small spine on each side. Second segment of outer 

 ramus shorter than the first ; third segment represented 

 by two spines, the inner the longer and pointed 

 obliquely outward. Inner ramus reaching end of first 

 segment of outer ramus ; apex hairy and armed with 

 two spines. Antennae reaching end of furcal setae. 



reighardi. 



41 (40). First abdominal segment as long as remainder of 



abdomen ; dilated laterally but unarmed. Last tho- 

 racic segment produced, armed with one small spine on 

 each side. Head partially divided by a suture. Third 

 segment of outer ramus represented by two spines, the 

 inner smooth, about twice as long as the outer, which 

 is delicately hairy. Inner ramus hairy, armed with 

 two long subequal spines. Antennae reaching beyond 

 end of furca. pallidus. 



42 (39). Furca about equal to third abdominal segment. 



43 (44). First abdominal segment about as long as remainder 



of abdomen and armed with small spines, equal on the 

 two sides. First thoracic segment armed with small 

 spine on each side. Second segment of outer ramus 

 shorter than the first ; third segment represented by 

 two spines, the inner about twice as long as the outer. 

 Inner ramus longer than first segment of outer ramus ; 

 hairy, armed with two spines, the inner twice as long 

 as the outer; margins sinuously curved. Antennae 

 reaching beyond tip of furca. sicilis. 



44 (43). First segment of abdomen as long as remainder of 



abdomen; armed with two large lateral spines, the 



