Monstrilloid copepods from a series of zooplankton samples collected in the coastal area of Miami, Florida, were examined taxonomically. Several adult females were found to belong to an undescribed species of Cymbasoma within the C. rigidum species complex. It can be distinguished from its congeners by the body proportions, shape of head, cephalic ornamentation pattern, genital double somite with straight lateral margins, and structure of the fifth legs, which have a small, inner lobe arising from the distal 1/5 of segment. This species shows intraspecific variability in some characters (i.e. shape of head, cephalic and genital ornamentation patterns); hitherto, such variation has been reported only in another species of Cymbasoma. Our finding supports the idea of the nominal species C. rigidum comprising a taxonomic complex with several undescribed taxa. The other species recorded in the area was Cymbasoma quadridens Davis, 1947. This was first described from a single male specimen collected in 1947 in Biscayne Bay, Florida, and has not been recorded thereafter. The type specimen now being unusable, this species is redescribed herein based on another topotypic male specimen collected near the type locality. New data are added about the armature of its antennules and swimming legs, cuticular ornamentation, and structure of the genital complex.