Ostracod-filled Elimia tenera from Laney MBr. Green River Shale Eocene Sweetwater County, Wyoming, purchased from SDFossils from ebay Sept 2017.
Elimia tenera, formerly known as Goniobasis tenera, is an extinct species of freshwater gastropods (snail) with an operculum, in the aquatic gastropod mollusk family (Wikipedia).
Picture of these fossilised snails (Elimia tenera):
Ostracods, or ostracodes, are a class of the Crustacea, sometimes known as seed shrimp. Some 70,000 species have been identified, grouped into several orders (Wikipedia).
Picture of modern Ostracod:
I like this fossil thin section as it contains fossils within fossils which can be seen in the microscopy photos below.
My photos of Ostracod-filled Elimia tenera through Zeiss IM microscope (Bresser MikrOkular camera):