Redescription of Janaria mirabilis, a calcified hydroid from the Eastern Pacific by Stephen D. Cairns and J. Laurens Barnard. Bull. Southern California Acad. Sci., 83(1): 1-11, 1984. Janaria mirabilis is redescribed and illustrated based on scanning electron microscopy (SEM) of the corallum, SEM of critical-point-dried decalcified specimens, and histology of decalcified specimens. Three types of gastrozooids are distinguished and the gonozooids were found to be superficial stalked structures, not ampullate as previously suggested. The resemblance of J. mirabilis to certain bryozoans is discussed and it is also compared to the other two Recent calcified hydractiniids now known. J. mirabilis is considered an important evolutionary link between the hydractiniid hydroids and the stylasterid hydrocorals in that both probably had a common ancestor in the Paleocene. The commonly occuring vesicles of J. mirabilis are hypothesized to be symbionts of some kind. Twenty new records of J. mirabilis, including 118 specimens, are reported, extending its distribution south to Panama.