The poorly-known genus Conosimus Mulsant et Rey, 1855 (Hemiptera: Fulgoroidea: Issidae) includes six species and is briefly reviewed. Adults and fifth instars of a new species, Conosimus baenai n. sp., are described and compared with other species in the genus. The new species is associated with an endemic shrub, Echinospartum boissieri, in Jaen, Spain, in the south of the Iberian Peninsula, one of the richest botanical areas of the Mediterranean Basin.