Anchistropus minor. 309 



I do not know whether Forbes' ('90, p. 712) paper was issued 

 earlier in the year than Sars' or not. In any case both species 

 had been described by their author some years before the pub- 

 lishing of the papers referred to. 



The shell is highest in the middle, "dorso medio distincte 

 angulato vel gibbo" (Sars). "The anterior dorsal surface is 

 flattened, meeting the flattened valves at an acute projecting 

 angle, giving the shell a trigonal form like a beech nut" 

 (Forbes). This shape is best seen when the animal is viewed 

 obliquely from above. The posterior dorsal margin slopes 

 steeply down to the posterior margin, which it meets at a 

 rounded angle. The posterior margin rounds over into the 

 ventral. The marginal hairs are stout. 



The head is small, movable, and in many of my specimens, 

 the apex of the beak was curved slightly forward. The macula j — * 

 nigra is larger than the pigment of the eye, and is nearer the 

 latter than to the apex of the rostrum. I have not seen it 

 twice as far from the rostrum as from the eye. 



The shell is reticulated with hexagonal meshes. I have been 

 unable to find the minute rugosities of which Forbes speaks. 

 The outlines of the regular meshes are sometimes resolvable 

 into minute elevations. The valves are always somewhat dirty 

 and rough. 



The post-abdomen is large, broad, with 8-10 stout teeth. The 

 anal tubercle is large, forming an acute projection. The caudal 

 claws are smooth. Length, 0.5 mm. Height, 0.37 mm. 



Anchistropus minor, sp. nov. 



Plate XIII, Figs. 2, 3, 4, 5. 



In my former paper on the Cladocera of Madison (Birge, '91, 

 p. 380) I stated that "a single specimen was found in lake 

 Wingra, belonging to the genus Anchistropus, Sars, and appar- 

 ently not to the species emarginatus, Sars. It was accidentally 

 destroyed before it could be carefully studied. " Other speci- 

 mens have been obtained in dredgings from lake Winnebago, 

 near Oshkosh, and from Gogebic lake, Michigan, so closely re- 



