''Casterolimulus'' is an extinct genus of

xiphosuran Xiphosura () is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Limulidae). They first appeared in the Hirnantian (Late Ordovician). Current ...

. It is known from the Late Cretaceous

Fox Hills Formation The Fox Hills Formation is a Cretaceous geologic formation in the northwestern Great Plains of North America. It is present from Alberta on the north to Colorado in the south. Fossil remains of dinosaurs, including tyrannosaurs, as well as larg ...

of North America, and it lived in freshwater environments. It is a member of the family

Limulidae Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are chelicerates, most closely related to arach ...

, and is placed as a close relative of ''

Victalimulus ''Victalimulus'' is an extinct genus of horseshoe crab, from Early Cretaceous (Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or ...

'' from the Early Cretaceous of Australia.

References

Xiphosura {{Paleo-arthropod-stub