21153 - Premium Grade Soft Bodied Xiphosurid (Horseshoe Crab Ancestor) Lower Ordovician Rare falcoid ribs that spring in

falcoid ribs that spring in pairs from umbilical tubercles

So Methodist Univ

Enstatite chondrites (type 4-7)

Other known institutional specimens include 370 g (ASU)

Teeth heavy with smooth enamel surfaces

21153 - Premium Grade Soft Bodied Xiphosurid (Horseshoe Crab Ancestor) Lower Ordovician Rare falcoid ribs that spring inXiphosurans are an order of arthropods related to arachnids, or, according to one recent study, actually arachnids. They are sometimes called horseshoe crabs (a name applied more specifically to the only extant family, Limulidae). They first appeared in the Tremadocian (Lower Ordovician) from Fezouata Fm in South Morocco. Currently, there are only four living species. They are members of the order Xiphosura, which contains two suborders, Xiphosurida