The North American species of Psathyrella.

306 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN [VOL. 24
Key to the Species of Subsection Mesosporae
1. Pileus sharply conic; veil rudimentary; pigment incrusting the hyphae of the subcuticular region of the pileus; growing gregarious on chip-dirt.
275. P. acutoconica.
1. Pileus obtuse when young. 2
2. Growing on tundra-like areas above tree line; subcuticular hyphae heavily
pigmented. 276. P. rainierensis.
2. Not as above. 3
3. Spore apex truncate from apical pore (or with a prominent lens-shaped hyaline cap). 4
3. Spore apex not or only indistinctly truncate. 12
4. Pileus silky; lamellae bluish gray when mature. 277. P. subsericea.
4. Not as above. 5
5. Spores (on 4-spored basidia) 9-12 X 7-9 u; on clay soil in Cuba (see 315.
P. ammophila also). 278. P. cubensis.
5. Spores narrower than in above choice. 6
6. Lignicolus; growing on beech wood. 279. P. fagetorum.
6. Growing on debris, mosses or soil. 7
7. Pileus pinkish on margin when faded; pleurocystidia 36-48 X 10-16 tu (if pleurocystidia up to 85 u long see P. superiorensis, also see P. duplicata).
280. P. orbitarum.
7. Not with above combination of features. 8
8. Brachybasidioles present in mature hymenium. 9
8. Not as above. 10
9. Veil lacking; stipe 3-3.5 mm thick. 281. P. pseudolongipes.
9. Veil present, of coarse fibrils, soon vanishing. 282. P. roothaanensis.
10. Lamellae dark vinaceous-brown at maturity; caulocystidia with flexuous
refractive walls. 283. P. cheyennensis.
10. Lamellae near "benzo brown" (violaceous-drab) at maturity. 11
11. Stipe rather stiff-cartilaginous, 1-1.5 mm thick, watery white and unchanging (see
405. P. nimkeae also). 284. P. duplicata.
11. Stipe distinctly fragile. 285. P. barlowiana.
12. Many pleurocystidia with 2-3 finger-like extensions near apex; growing on
black mulch in Thuja swamps. 286. P. thujina.
12. Not as above. 13
13. Stipe about 1 mm or less thick; transverse septa of hyphae of cortex of the stipe
highly colored in KOH. 287. P. pseudofulvescens.
13. Not as above. 14
14. Pleurocystidia mostly under 60,u long; spores 8-11 X 5-6.5 uA; pileus chestnut
brown moist. 288. P. clivensis.
14. Not as above. 15
15. Pileus cuticle an hymeniform layer of pear-shaped cells. 289. P. subhepatica.
15. Pileus cuticle a cellular layer 2-3 cells deep (see 414. P. velatipes also). 16
16. Veil absent; pleurocystidia with greatly elongated necks. 290. P. ruderaria.
16. Veil present; pleurocystidia 48-62 /, long; stipe shining and not discolored
in age. 291. P. nitens.
275. Psathyrella acutoconica A. H. Smith, sp. nov.
Pileus 8-15 mm latus, acute conicus, fusco-cinnamomeo-brunneus glaber;
lamellae confertae, latae, brunneolae demum fusco-violaceae; stipes 3-5 cm
longus, circa 1 mm crassus, pallidus, deorsum demum brunneus; sporae 10-12.5 x
5-6.5 pu; pleurocystidia 34-50 x 9-16 p, ventricosa, rostrata, vel fusoideoventricosa, acuta; fibulae adsunt. Typus. Smith 27275 (MICH); legit prope
Dexter, Michigan.
Illust. Text Figs. 585-587.
Pileus 8-15 mm broad, sharply conic, expanding to conic-campanulate, surface
glabrous, moist, hygrophanous, "Mars brown" when fresh, fading to near
cinnamon-buff or pinkish buff, in old caps nearer avellaneous when faded or