Jurassic Park Wiki

Mesolimulus is an extinct genus of arthropod. The best known examples are found in Solnhofen limestone near Solnhofen, Bavaria, Germany. Originally assigned to the living genus Limulus, they are related to and look virtually identical to extant horseshoe crab species.

Wikipedia has a more detailed and comprehensive article on Mesolimulus

Jurassic Park

Mesolimulus has never appeared or mentioned in any Jurassic Park films or books, it has however appeared in the PC version of Jurassic Park and in Jurassic Park III: Park Builder.