The carapace of the prosoma was unsegmented and often bore a pair of eyes.
ad, Muscle from carapace to entosternum.
In Homola the carapace is quadrilateral.
The general form and structure of their prosomatic carapace are in many striking features identical with that of Limulus.
The bivalved carapace has a jointed rostrum, and covers only the front part of the body, to which it is only attached quite in front, the valve-like sides being under control of an adductor muscle.