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 
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- 
