Key to Arthromyces and Blastosporella in the Neotropics, insect associated taxa arising from aggregated masses of insect faecal pellets

1. Pileus mostly plane, up to 40 mm broad, brown, translucent-striate, hygrophanous, glabrous and not producing arthroconidia on the pileus or stipe (currently known only from Brazil and Guyana) .............................................................................. A. glabriceps

- Pileus variously shaped, but always producing dark brown or fuscous black powdery conidia........................................................2

2. Pileus truncate-convex and strongly zonate at first with gray and dark brown bands, soon deeply depressed over disc producing a well-defined rim around the disc with the depression filled with powdery soot-brown blastospores produced by inflated hyphal end cells on the pileus, blastospores globose and strongly tuberculate ornamented (Colombia and Dominican Republic) ............... ........................................................................................................................................................................... Blastosporella zonata

- Pileus not strongly zonate nor depressed with well-defined rim around the disc, pileus variously shaped and producing dark gray or grayish-brown arthroconidia in chains of disarticulating end cells on the pileus and in one species also the stipe......................3

3. Pileus with well-developed, thick, pale grayish-cream colored marginal roll at first, which turns olivaceous-brown and powderypulverulent from production of long chains (10–20 cells) of smooth walled, dark brown arthroconidia, cheilocystidia narrowly clavate or cylindrical-capitate and not encrusted (Colombia) ................................................................... Arthromyces pulverulentus

- Pileus lacking well-developed, thick marginal roll, arthroconidia verrucose or punctate roughened, typically in chains of less than 10 cells, cheilocystidia with resin-encrusted apices ..........................................................................................................................4.

4. Pileus up to 55 mm broad, convex and grayish-yellow to clay color, margin translucent-striate at first, pileus disc area soon developing dark grayish-brown powdery arthroconidia and production of arthroconidia spreading towards the margin, arthroconidia dark brown and finely punctate ornamented over the outer walls (Belize and Florida, USA) ......................... Arthromyces matolae

- Pileus up to 15 mm broad, ± convex, typically with broadly truncate disc which is strongly depressed with age, pileus margin strongly inrolled, entire pileus opaque; pileus and stipe densely covered with short chains of powdery dark brown verrucose ornamented arthroconidia (Dominican Republic, Puerto Rico) ................................................................... Arthromyces claviformis