North American Species of Diaptomus. 151 



The above description is compiled from Herrick's first 

 paper on this species ('95) and from the figures and the 

 English and Latin descriptions in his later paper (Herrick 

 ai d Turner, '95). Both of these articles are published as 

 original descriptions, although there was nine months' differ- 

 ence in the time of their appearance. 



Diaptomus oreg-onensis Lilljeborg. (PL XXIX., Fig. 

 1, 2.) 



Diaptomus oregonensis, de Guerne et Richard. '89b, p. 53, PI. II., Fig. 



5; PI. III.. Fig. 8. 

 Diaptomus oregonensis, Marsh, '93, p. 200, PI. IV., Fig. 4, 5. 

 Diax>tomus oregonensis, Marsh, '95, p. 8, PI. VII., Fig. 5. 

 Diaptomus oregonens is, Herrick and Turner, '95. p. 72, PI. IV., Fig. 



7-12 ; PI. IX., Fig. 3. 



A species of medium size. Cephalothorax widest about 

 the middle. The last two thoracic segments confluent above, 

 the last one, seen from above, slightly produced laterally, 

 bluntly rounded but unarmed ; in the male armed with two 

 very minute spines on each side. First abdominal segment 

 as long as the rest of the abdomen.* Third segment and 

 furcal rami subequal, the latter about one and a half times 

 as long as broad and delicately hairy within. In the male 

 the first abdominal segment is short and unarmed ; second 

 and third segments and furcal rami about equal ; fourth 

 segment the longest, about equal in length to the first two 

 segments taken together. Furcal rami about as in the female. 



Antennae of the female 25 -segmented, extending beyond the 

 tips of the furcal seta?. Prehensile antenna of the male but 

 slightly swollen, the antepenultimate article entirely unarmed. 



First basal segment of fifth leg of female (PI. XXIX., Fig. 

 2) with the usual delicate hair on the outer margin. First 

 segment of outer ramus about twice as long as wide, slightly 

 arcuate, margins parallel ; second segment about as long as 

 the first, moderately curved, terminating in an acute point, 



*This segment hart a very peculiar appearance. Owing to the thicker anterior 

 part, the segment seemert to have a suture at about the middle, and this was so mis- 

 leading that I doubted if the specimens on the slides were really females until I could 

 see the antennae, and not until 1 could get a side view was I at all certain that there 

 was only one segment. 



