Synopsis.Hammondia pardalssp. n. (Eimeriorina: Sarcocystidae) from Panama Canal Zone is described as an obligate heteroxenous coccidian, with felids as the final host and laboratory mice as the experimental intermediate host. Ovoid oocysts. measuring 40.8 (36–46) × 28.5 (25–35) m̈m. are shed unsporulated. Oocysts were infective only for the intermediate host. the laboratory mouse,Mus musculus, and the intracellular cysts were infective only for felids. Attempted passage of tissue cysts from mouse to mouse was unsuccessful.Mice fed 5 × 104sporulated oocysts were found to harbor small intracellular cysts, 13–16 × 10–15 m̈m, in the mesenteric lymph nodes, lungs, and intestinal submucosa 15 days postinfection. The meronts in these early cysts were stubby and measured 3 × 6 m̈m. The prepatent period in the felids was 5 to 8 days and the patent period 5–13 days. Experimental infections of definitive hosts were successful with 6/6 domestic laboratory‐reared kittens,Felis catus; 5/5 ocelots,F. pardalis; and 1/1 jaguarundi,F. yagouaroundi.None of the exposed raccoons,Procyon l