OO Capillitium marked by sharp-edged transverse plates and by numerous nodes 6. _A. nodulosa_ OOO Capillitium marked by close reticulations 7. _A. ferruginea_ _B._ Capillitium persistently attached to the calyculus. _a._ Sporangia reddish brown, etc. 8. _A. denudata_ _b._ Sporangia gray or ashen i. Simple 9. _A. cinerea_ ii. Clustered 10. _A. digitata_ _c._ Sporangia yellow 11. _A. pomiformis_ _d._ Sporangia rose-colored, .5-1.5 mm. 12. _A. insignis_ 1. ARCYRIA MAGNA _Rex._ 1893. _Arcyria magna_ Rex, _Proc. Phil. Acad._, p. 364. Sporangia densely aggregated, forming clusters of greater or less extent, sometimes reaching several centimetres in either direction, tawny gray or ashen, cylindric, tapering a little above, when expanded reaching a length of half a centimetre or more, stipitate; peridium evanescent except the small shallow cup-like base, the calyculus; stipe long (1 mm.), weak, pale brown or reddish, tubular, the channel filled with plasmodic masses; capillitium gray or drab-colored, very slightly attached to the bottom of the calyculus, far expanded, forming a loose-meshed net, the threads regular, cylindric, coarsely sculptured with rings, half-rings, cogs, spines, etc.; spores in mass dull gray, drab, under the lens colorless, papillate, with few papillae, 7-8 mu. This magnificent form resembles in habit and general appearance, save color, _A. nutans_. The capillitium is, however, very different both in the sculpture and in the more delicate markings of the threads. Dr. Rex, _l. c._, has pointed out the lack of reticulation on the capillitium and calyculus. The color is also diagnostic. A roseate variety seems to occur with the present form. This is _A. magna rosea_ Rex, and appears to agree with the type in all respects save color. The relationship here must be determined by future inquiry. The capillitial threads are remarkable for their graceful slenderness, regularity, and symmetry. 2. ARCYRIA OERSTEDTII _Rost._ 1875. _Arcyria oerstedtii_ Rost., _Mon._, p. 278, Fig. 196. Sporangia cylindric, arcuate, 1.5 mm. high when unexpanded, closely clustered, dull crimson, stipitate; peridium evanescent except here and there a persistent patch, the calyculus shallow, plicate, papillose within; stipe short, weak, concolorous; hypothallus distinct, membranous, concolorous; capillitium a loose, far-expanding, elastic net, the meshes uneven, often small, the threads characterized by much irregularity and many bulbose thickenings, especially at the nodes, strongly spinulose throughout; spore-mass crimson or reddish brown, dull; spores by transmitted light colorless, nearly smooth, sub-globose, 9-10 mu.