North American Species of Diaptomus. 149 



segment is sometimes armed at the outer distal angle with 

 a short, sharp spine. 



Herrick (Herrick and Turner, '95) states that he found the 

 second segment of the left fifth leg of the male to be granular 

 on the inner margin, and the marginal spine of the right leg 

 denticulate on the inner margin and at the base. In both 

 these respects my specimens differ from his, the second seg- 

 ment of the left foot being hairy instead of granular, and 

 the marginal spine of the right foot perfectly smooth. Her- 

 rick's statement that "the first pair of antennae reach to the 

 extremity of the furca or surpass them" leads me to think 

 that they are longer in the Florida specimens than in his, 

 since they clearly reach beyond the tips of the f ureal setse in 

 every individual which I have examined. 



In New Mexico Herrick found this species, in connection 

 with D. novamexicanus, in the water supply of the city of 

 Albuquerque; but in the Florida lakes it was found with 

 I). mississippiensis Marsh, the two forms being about equally 

 abundant. They are very much alike in general appearance, 

 but the males may be distinguished without dissection by the 

 antepenultimate article of the right antenna, which is armed 

 in D. albaquerquensis while it is unarmed in D. mississippien- 

 sis. Herrick gives the length of the female as 1.4-1.6 mm., 

 but the largest female from Florida was 1.2 mm., while the 

 male was only 1.05 mm. in length, the average being con- 

 siderably smaller. 



Diaptomus novamexicanus Herrick. 



Diaptomus novomexicanus , Herrick, '95, p. 46, Fig. 27-29. 

 Diaptomus novamexicanus, Herrick and Turner, '95, p. 70, PI. VI., 

 Fig. 7-10. 



Among the smaller species of the genus, moderately robust. 

 Cephalothorax widest somewhat in front of the middle. Last 

 two thoracic segments distinct, the last armed on each side 

 with a small, short spine. First abdominal segment very 

 long, much exceeding the remainder of the abdomen, pro- 

 vided on each side with a short, sharp spine; second seg- 

 ment the shortest. Furcal rami equal in length to the 



