ut variable markings; 9-10 mu.
Seattle, Washington.

Differs from _D. nigripes_ in color of the stipes, capillitium,
spore-diameter, etc.

15. DIDYMIUM DUBIUM _Rost._

1875. _Didymium dubium_ Rost., _Mon._, p. 152.
1892. _Didymium listeri_ Mass., _Mon._, p. 244.
1894. _Didymium dubium_ Rost., List., _Mycetozoa_, p. 95.
1911. _Didymium dubium_ Rost., List., _Mycetozoa, 2nd ed._, p. 126.

Fructification wholly plasmodiocarpous, snow-white, small,
2-6 mm., flat and thin; the outer wall double, membranous within,
calcareous-crystalline without; columella none; capillitium simple of
rather thick, vertical, brown threads, sparingly united laterally, and
only occasionally furcate at the ends, especially above; spores minutely
spinulescent, violaceous pale, 12-15 mu.

Massee thought English specimens out of harmony with the original
description and gave them a new name. To refuse this, Lister enlarges
the range of spore-measurements and disregards some of Rostafinski's
specifications as to capillitium. Our specimens are as described.

Bohemia. England. Shores of Lake Okoboji, Iowa.

This is indeed a doubtful form. It differs from _D. difforme_ chiefly in
that the outer calcareous shell is not smooth, but is covered with
abundant loose crystals, frosted. The spores are paler but about the
same size. The frosting may be incident to local climatic conditions at
the time and place of desiccation.

16. DIDYMIUM DIFFORME _Duby._

1797. _Diderma difforme_ Pers. _Tentamen Disp. Meth._, p. 19.
1830. _Didymium difforme_ Duby., _Bot. Gall._, ii., p. 858.
1875. _Chondrioderma difforme_ Pers., Rost., _Mon._, p. 177.
1894. _Didymium difforme_ Duby., List., _Mycetozoa_, p. 94.
1899. _Diderma personii_ Macbr., _N. A. S._, p. 96.
1911. _Didymium difforme_ Duby., List., _Mycetozoa, 2nd ed._, p. 124.

Plasmodiocarpous, the smooth, white outer peridium separable from the
thin, colorless or purplish inner layer; capillitium of rather coarse,
flat, dichotomously branching threads, broader below; spores minutely
warted, or almost smooth, dark brown, 12-14 mu.

The white crust-like outer wall has more than once carried this species
into _Diderma_. It is still doubtful whether we are here dealing with
_Chondrioderma calcareum_ Rost. Miss Lister cites a variety, _S.
difforme comatum_, with more abundant capillitium which may represent
Rostafinski's species.

Evidently rare in the United States; reported more co