Lister has examined Rostafinski's type of C. reticulatum and declares that it has the usual didermic characters. Hence there is no doubt that our small-spored American specimens are covered by Rostafinski's description, No. 72. On the other hand, Lister makes C. difforme (Pers.) Rost. a Didymium, by its crystalline coat. That species therefore is removed from consideration in this connection. C. calcareum remains as applicable to American forms having the spores 10–12 µ, but according to the author of the species the capillitium is abundant and definitive. Unhappily the type of C. calcareum is lost (Lister, Mon., p. 95), so that there is no other means of verification than the description and Rostafinski's figure. Under these circumstances we consider the name calcareum inapplicable to any American forms we have so far seen. See next species. As to the American species which have been distributed as C. calcareum (Lk.) Rost., they are, so far as seen, referable to D. reticulatum (Rost.), Morg. Here also belongs No. 1217, Ellis, N. A. F.

New York, Pennsylvania, Ohio, Iowa, Nebraska. Probably to be found throughout the eastern United States.

2. Diderma spumarioides Fries.

Sporangia sessile, crowded, spherical, or by mutual pressure irregular, white; the peridium plainly double, but the layers adhering, the outer more strongly calcareous, but very frail, almost farinaceous; hypothallus more or less plainly in evidence, white or pale alutaceous; columella distinct, though often small, globose, yellowish; capillitium variable in quantity, sometimes abundant, brown, somewhat branching and anastomosing outwardly, the tips paler; spores minutely roughened, dark violaceous, about 10 µ.

This species has the outward seeming of a didymium, but is plainly different as that genus is here defined, since the calcareous crust, although inclined to be pulverulent, is made up of minute granules, not crystals, of lime. The hypothallus is sometimes hardly discoverable, anon well developed, out-spread, rugulose, far beyond the limits of the fructification. In his Monograph, p. 175, Rostafinski includes here Physarum stromateum Link. In the Appendix he is inclined to raise Link's form to the dignity of a distinct species, basing the diagnosis upon the superposition of the sporangia in certain cases, a feature entirely unknown to Link's description and of extremely uncertain value, since by their crowding the sporangia are liable always to be pushed above each other. We therefore regard C. stromateum (Link) Rost. as a synonym of the present species, as the description, Link, Handb., III., 409, indicates, so far as it goes.

3. Diderma simplex (Schroet.) Lister.

"Plasmodium bright yellowish brown." Sporangia gregarious, sessile, globose or depressed globose, .3–.5 mm., or anon plasmodiocarpous, brown or brick-red when fresh, becoming paler, ochraceous, etc.; hypothallus everywhere in evidence; columella ill-defined; capillitium scanty, the threads delicate, pale, branching as they join the peridial wall; spores dull violaceous, slightly roughened, 8–10 µ.

A rather crude, primitive representative of this beautiful genus. The inner peridium seems to be lacking,—a comfort to Rostafinski! Rare. Our best specimens are from New Jersey, by courtesy of Dr. C. L. Shear. These went to fruit on leaves and branches of Vaccinium. It seems to affect the heather of Europe, moorland, etc. I have also specimens from the herbarium of the lamented Dr. Rex. These are more plasmodiocarpous, but open beautifully by a median fissure as in Physarum sinuosum Bull. In no American gathering that I have examined does the capillitium show calcareous thickenings as described by the British text.