OLIVE : MONOGRAPH OF THE ACRASIEAE. 
507 
Dictyostelium purpureum Olive. Plate 7, fig. 98-104. 
Proc. Amer. acad. arts and sci., vol. 37, p. 340, 1901. 
Sorus and stalk purplish or violet; when mature, almost black. 
Sjjores oval, rarely somewhat inequilateral, 3 p,-5 /x by 5 /x-8 /x. 
Dung of mouse, toad, cow, horse, sheep, muskrat. Cambridge, 
Mass.; Indiana; Florida. 
This distinct species, well marked by its color, was collected in 
August, 1897, in Crawfordsville, Indiana, on mouse dung cultures, 
and in October of the same year by Dr. Thaxter in Eustis, Florida, 
on toad dung. Both forms have been cultivated ever since in the 
laboratory, with no particular precautions as to the dissemination of 
the spores, and it is not impossible that the fructifications which 
appeared at Cambridge on substrata other than the two just men¬ 
tioned, represent laboratory escapes. 
Dictyostelium aureum Olive. Plate 6, fig. 63-64. 
Proc. Amer. acad. arts and sci., vol. 37, p. 340, 1901., 
Mature sori light to golden yellow, 1.5 mm.—4 mm. high. Spores 
oval, or frequently inequilateral, 2.5 /x-3 /x by 5 /x-8 fx. Mouse dung 
from Porto Rico. 
This species, communicated by Dr. Thaxter, is quite well defined 
through the color of its fructifications, but especially so by its myx- 
amoebae and its manner of growth. It matures very slowly on a 
horse dung decoction or on other media especially favorable for the 
rapid development of the common species; while the myxamoebae, 
instead of possessing the usual form with elongated, sharp pseudo¬ 
podia, are in general irregularly lobed and nodulated, even when 
growing under normal conditions. Such irregular shapes are similar 
to those assumed by the myxamoebae of other species when they 
are growing under such abnormal conditions as are furnished by an 
insufficient water supply. 
Polysphondylium Brefeld, 1884. 
Plates 6, 7, 8. 
Schimmelpilze, bd. 6, p. 1-34, pi. 1-2, 1884. 
Sori spherical, borne terminally on primary and secondary stalks, 
the latter branching in whorls from the main axis ; the fructification 
occasionally simple as in Dictyostelium. Whorls varying in number 
from 1 to 10, and the number of branches at each node from 1 to 6. 
