One of the smallest species of the genus, by its proportionally long stipe and small round sporangium reminding one somewhat of _P. globuliferum_; much smaller, however, and in every way different. The generic characters are mixed, and the species has been accordingly variously referred. The lower part of the peridium is sometimes persistent after the dehiscence, and so far reminds of _Craterium_. But this character is not constant, and even at best the persisting part is very small, not greater than in _P. melleum_, for example. On the other hand, the capillitium in some sporangia is strongly calcareous, reminds of _Badhamia_, but in most sporangia the _Physarum_ characters are sufficiently clear. In the Kew Herbarium, it is said, are two American specimens under one label, "_Didymium pusillum_." One specimen is a didymium indeed, but, as it appears, _D. proximum_ Berk., already described. The other is a physarum. It is proposed in _Mycetozoa, 2nd ed._, to use the combination thus set free, as if applied by the original author to the second specimen, _not_ didymium, and to make the new combination date from 1873 and so take precedence of the binomial applied in 1881 by Cooke and Balfour here retained by the law of priority. 35. PHYSARUM MACULATUM _Macbr._ PLATE XIV., Figs. 6, 6 _a_, 6 _b_. 1893. _Bull. Lab. Nat. Hist. Iowa_, II., p. 383. 1899. _Physarum maculatum_ Macbr., _N. A. S._, p. 47. 1911. _Physarum tenerum_ Rex., Lister, _Mycetozoa_, p. 52, in part. Sporangia scattered or gregarious, very small, .3-.4 mm., dull gray, thin-walled, dotted with minute, white calcareous granules, stipitate; stipe long, about 2 mm., stout, attenuated upward, striate longitudinally or wrinkled, filled with irregular yellow masses of lime and accordingly bright yellow in color; columella none; capillitium forming a dense net, with comparatively small yellow nodular thickenings; spores globose, purplish, each minutely papillose and displaying several scattered spots occasioned by local development of the papillae; diameter of the spores 9-10 mu. This species was set up for the reception of certain material collected by Professor Shimek, in 1892, in Nicaragua. It remains so far unique. The small globose sporangium mounted upon a long upwardly tapering stipe, .5 mm. thick below, but narrowed at the extreme base where it is lightly attached, a stem which is simply a sack stuffed with yellow lime-granules;--this and the yellow capillitium are distinguishing features. The capillitium and spores suggest _Tilmadoche viride_, but the entire habit precludes such reference. Perhaps nearest to _P. melleum_. Castillo, Nicaragua. Miss Lister thinks this the same as _P. tenerum_ Rex. But the whole habit and external appearance are different; the stipe notably long, clumsy, surcharged with lime; a very singular form. 36. PHYSARUM DIDERMOIDES (_Pers._) _Rost._ PLATE IX., Figs. 1, 1 _a_, 1 _b_, 1 _c_.