Clathroceras
Clathroceras is an extinct genus of straight oncocerid belonging to the family Trimeroceratidae. It comprises several species, including Clathroceras plicatum and C. sulcatum. C. plicatum was discovered in Gotland, Sweden, and C. sulcatum in the Czech Republic. The latter was originally classified as part of the distantly-related oncocerid genus Phragmoceras. References 

Oncocerida
Prehistoric nautiloid genera
Silurian animals
Silurian animals of Europe