North Americdu Species of Diaptomus. 167 



Diaptomus ashlandi Marsh. (PL XXXII., Fig. 1-4.) 



Diaptomus sicilis var. imperfectus , Forbes '90, p. 703. 

 Diaptovnis ashlandi, Marsh, '93, p. 198, PI. III., Fig. 11-13. 

 Diaptomus ashlandi, Herrick and Turner, '95, p. GO, PI. VI., Fig. 4-6. 

 Diaptonms ashlandi. Marsh, '95, p. 7, PL VIl., Fig. 2. 



A small, slender species, about the same width throughout. 

 Suture between head and thorax distinct. Last two thoracic 

 segments distinct, the last one strongly bifid and armed on 

 each side with a small blunt spine. Abdomen long and 

 narrow ; inclusive of the furca, about half as long as the ceph- 

 alothorax. First abdominal segment as long as the remainder 

 of the abdomen exclusive of the furcal rami ; dilated laterally ; 

 with a small spine on each side (unarmed in the male). Second 

 and third segments subequal. Furcal rami barely twice as 

 long as wide ; hairy within. 



AntenniTB 2 5 -segmented, reaching to the base of the furcal 

 rami or slightly beyond. Prehensile antenna (PI. XXXII., 

 Fig. 4) moderately swollen; segments 19, 20, and 21, and 

 22 and 23, ankylosed ; process on the antepenultimate seg- 

 ment extending almost to the middle of the last segment, the 

 end knobbed and roughened or tuberculate at the inner 

 margin. 



Fifth pair of legs of the male (PL XXXII., Fig. 3) rather 

 slender ; left leg reaching about to the end of the first seg- 

 ment of the outer ramus of the right leg. On the anterior 

 surface of the first basal segment of the right leg is a large 

 tubercle bearing at the tip a small acute spine. Second 

 basal segment without special characteristics. First seg- 

 ment of the outer ramus subquadrate, slightly broader than 

 long ; inner apical angle somewhat produced, the process 

 ending in an acute point. Second segment about three times 

 as long as the first, with a sharp angle at end of proximal 

 third, from the point of which springs the lateral spine. This 

 is about half as long as the segment, with an angle near its 

 base. Terminal hook long and slender, rather more robust 

 than that of T). slcilis Forbes, but shaped very much like it; 

 minutely denticulate on the inner margin. 



