The preceding description is based on material assembled during forty years. The form is easily discoverable by any collector throughout the entire valley of the Mississippi and eastward to Nova Scotia. For its naming, students in America have vainly waited the decision of those having access to mycologic types in Europe. It seems now certain that the species is extremely rare in the old world if there occurrent; never seen by any of the earlier taxonomists including Fries and Rostafinski; perhaps adventitious in these later years, although thus far no specimen from Europe has reached this table.[24] _P. nefroideum_ of Strasburg herbarium turns out, after all, _teste_ Lister, to be _P. compressum_ Alb. & Schw., which accordingly shall now enjoy state and station of its own; our concern in European nomenclature, in the present instance, almost disappears, and we return to our synonymy from this side of the sea. Mr. Lister would recur to Dr. Peck's _Didymium connatum_, which indeed represents the present species. In such disposition, how gladly would all concur, were the thing possible! But _Physarum connatum_ is already a synonym twice over.[25] Unless we are done with the rules entirely, _P. connatum_ cannot stand. _P. polymorphum_ and _P. leucophaeum_ are names already in use, of course; and so under the circumstances, much as it is to be regretted, there would seem nothing left to do but to cancel all past synonymy and impose a new name whose permanence may at least be hoped for, if not expected. 40. PHYSARUM TROPICALE _Macbr._ 1899. _Physarum tropicale_ Macbr., _N. A. S._, p. 45. PLATE XV., Figs. 4, 4 _a_, 4 _b_. Sporangia scattered, gregarious, turbinate, short stipitate, blue-gray, about 1 mm. in diameter; peridium above iridescent, green, blue, etc., dotted with minute flecks of white, below limeless, purple or bronze shading to the brown of the stipe; stipe short, stout, slightly rugose, cylindric, non-calcareous, brown; columella none; hypothallus none; capillitium abundant, the nodes generally calcareous, small, uniform, angular, white, uniformly distributed; spore-mass, black; spores dark violet-brown, distinctly and closely warted, 12-15 mu. A large handsome species recognizable by the peculiar turbinate sporangium, with its iridescent peridial wall in which green strongly predominates above, bronze below. The distinction between the upper and lower peridium would suggest _Craterium_, but the internal structure is not at all _Craterium_-like. The capillitium is typically of _Physarum_. The color suggests _P. leucophaeum violascens_ Rost. From this species it is at once distinguished by its much longer sporangia, larger and rougher spores. Mexico; _C. L. Smith_: Sure to be again collected once that unhappy country shall again open its forests to research. 41. PHYSARUM NICARAGUENSE _Macbr._ PLATE XV., Figs. 7, 7 _a_, 7 _b_; XVII., 11 and 11 _a_.