BELONGING TO DAPHNIA AND OTHER ALLIED GENEEA. 221 



Daphnia hamata, n. sp. PI. YII., figs. 9-17. 



1884. ? Daphnia minnehaha, Herrick, A final report on the 

 Crustacea of Minnesota included in the orders Clado- 

 cera and Copepoda, p. 59, pi. K, figs. 1 , 2 ; pi. L, figs. 1,2. 



Female. — The outline as seen from the side (fig. 9) is subovate, 

 the head well rounded in front, sinuated below, and' produced 

 into a -wide truncated beak, the lower angle of which is sharp 

 and much exserted. The dorsal margin is only very slightly 

 curved, and its posterior extremity is extended into a long spine 

 which is directed backwards and upwards : ventral margin boldly 

 and evenly rounded ; both margins are fringed from a little be- 

 hind the middle with short spinules. The valves are pellucid, or 

 nearly so, and are entirely covered with a square reticulation. In 

 young specimens (fig. 11) the dorsum is straight, forming at its 

 junction with the head an obtuse angle which bears four short, 

 wide teeth, their points directed forwards (fig. 12). The anten- 

 nules are small and scarcely distinguishable from the beak except 

 by the presence of sensory setae. The basal joint of the antennae 

 in adult or subadult specimens, and to a smaller extent the fol- 

 lowing joints also, have a scaly appearance owing to the presence 

 of waved lines of minute bead-like hairs (fig. 17). The two 

 principal abdominal processes are distinct, and behind these are 

 two cushion-like prominences — all of them hispid ; the marginal 

 spines of the post-abdomen are eleven or twelve in number, short 

 and subequal ; terminal unguis rather deeply pigmented, bidentate 

 on the convex margin, and on the concave margin bearing four 

 or five large basal spines and a few bristles (fig. 16). The eye 

 is placed near the middle of the head, and the eye-spot is not 

 more than about one-half its diameter removed from it (fig. 10). 

 Length of adult, 2*53 mm. 



Male. — The head is simply rounded (fig. 18), the beak con- 

 sisting of a minute rounded prominence which bears a single 

 apical hair. The anterior dorsal angle of the shell is toothed 

 almost as in the young of the opposite sex (fig, 13). Antennule 

 short, cylindrical, otherwise as in D. pulex. Abdominal processes 

 straight, not setiferous. 



I have met with this species only in two gatherings made by 



