106 Wisconsin Academy of Sciences, Arts, and Letters. 



This and the following species will be more briefly described. 

 There is no evident angle at the junction of the dorsal and pos- 

 ■terior margins. The lower edge bears sette and has no sinns. 

 The front edge has a very slight sinus, or none at all. The 

 valves are marked by faint horizontal stri^. The rostrum does 

 not extend so far downwards as in the preceding species. The 

 post-abdomen has its usual claws, each with its basal spine, which 

 is not serrate. The teeth of the post-abdomen are about twelve 

 TO each row ; three or four at the end are larger than the rest. 

 There is besides, a row of hairs above the row of teeth. The 

 lower angle of the post-abdomen is not rounded. The male is of 

 the same general shape as the female. Length, 0.34, height, 

 ■0.18 mm. In the armature of the post-abdomen this species ap- 

 proaches nearest to A. tenuicaudis (Sars) ; but in other respects, 

 e. g. shape of shell, and especially of post-abdomen, is quite dif- 

 ferent. 



Cambridge, Mass., 1876.; Madison, Wis., July, 1877. Not com- 

 mon. 



SPECIES 3. 



Alona G-lacialis. sp. nov. 

 Length, 0.3 mm. Height, 0.19 mm. 



Anterior margin of valves without sinus. Yalves horizontally 

 striated. Lower corner of post-abdomen rounded. 



This species differs from the preceding chiefly in the post-ab- 

 domen. This is rounded at the lower angle, and the teeth, about 

 fourteen in number, are of equal size. There is also a second row 

 •of hairs. The forward edge of valve is strongly convex, other- 

 wise much like A. porrecta. This species approaches perhaps most 

 ■nearly to A. lineata (Fischer). There are, however, great dif- 

 ferences. The size of A. lineata is nearly twice as great. The 

 post-abdomen has, according to Mliller and Schodler, only one 

 row of teeth and no hairs. According to Kurz, it has hairs, but a 

 deep incision in the lower end. In either case the dtfference is 

 well marked. The shape is also different. A. glacialis is rela- 

 tively much broader behind than A. lineata (vid. Schodler). 



