Tulosesus amphithallus is a species of mushroom producing fungus in the family Psathyrellaceae.

[1] It was first described by mycologists Morten Lange and Alexander H. Smith in 1953 and classified as Coprinus amphithallus.

In 2001 a phylogenetic study resulted in a major reorganization and reshuffling of that genus and this species was transferred to Coprinellus.

[3] The cap is 0.6 to 1.2 cm (0.24 to 0.47 in) tall, and initially sharply conical in shape, but later expands to become bell-shaped (campanulate).

The spores are cylindrical and tapering (terete), and tend to vary in size, with dimensions ranging from 11.2 to 15.6 by 6.2–8.3 μm.