Key to species of Chasmocarcinus 1. Western Atlantic (Gulf of Mexico, Caribbean Sea to Brazil) in distribution....................................... 2 - Tropical Eastern Pacific (Lower California to Peru) in distribution............................................. 8 2. Anterolateral margins of carapace smooth, without conspicuous tubercles, convex (e.g., Fig. 21 A).................... 3 - Anterolateral margins of carapace elevated, with conspicuous tubercles, granules, or setose ridge (e.g., Fig. 21 C).........4 3. Anterior third portion of carapace proportionally narrow, anterior margin conspicuously narrower than median portion (Fig. 2 A‒D). Fingers of major chela of large males elongated, dactylus clearly longer than propodus (Fig. 35 A, C), curved in dorsal view (Figs. 2 A, B). Third maxilliped ischium elongated (Fig. 28 A‒C) [West Indies to Brazil]................. C. typicus - Anterior third portion of carapace nearly as wide as median portion (Fig. 3 A, B). Fingers of major chela of large males not elongated, dactylus only slightly longer than propodus (Fig. 35 I), straight in dorsal view (Fig. 3 A, B); third maxilliped ischium rectangular (Fig. 28 F) [Gulf of Mexico]............................................................ C. chacei 4. Dorsal surface of chelipeds with conspicuous setae (Fig. 3 G). Anterolateral margins of carapace with low, setose ridge (Fig. 21 H) [Brazil]............................................................................... C. hirsutipes - Dorsal surface of chelipeds smooth or with sparse setae or smooth (e.g., Fig. 3 E). Anterolateral margin of carapace with conspicuously raised, granular ridge, row of setae absent (e.g., Fig. 21 C, D)......................................... 5 5. Fingers of major chela of large males arched, leaving wide, circular gap (Fig. 35 E), curved in dorsal view (Coelho & Coelho 1998: figs. 1a, 2c). Dorsal surface of cheliped propodus of large males eroded (Fig. 35 E) [Brazil]............. C. arcuatus - Fingers of major chela of large males straight or slightly curved, not leaving wide, circular gap (e.g., Fig. 35 K). Dorsal surface of cheliped propodus of large males smooth............................................................... 6 6. Carapace proportionally wide along anterior third, almost as wide as posterior portion (Fig. 3 C‒E) [Florida and West Indies to Brazil]................................................................................... C. cylindricus - Carapace conspicuously narrower along anterior third than posterior portion (e.g., Fig. 4 G).......................... 7 7. Orbits, eye peduncles proportionally short (Fig. 22 D). Male telson proportionally short, broad (Fig. 50 E) [Brazil]........................................................................................................ C. meloi - Orbits, eye peduncles proportionally long (Fig. 22 E). Male telson proportionally long, narrow (Fig. 50 F) [Gulf of Mexico].......................................................................................... C. mississipiensis 8. Ambulatory legs proportionally short, merus wide, stout (e.g., Fig. 4 A). Fingers of major chela of large males almost straight (Fig. 36 E, G) [Gulf of California to Peru]............................................................ C. latipes - Ambulatory legs proportionally long, merus slender (Fig. 4 F). Fingers of major chela of large males gently or prominently curved (e.g., Fig. 36 A)................................................................................. 9 9. Pterygostomial region prominent, bulging, clearly visible from dorsal view (Fig. 5 C). Fingers of major chela of large males prominently curved, slender, long (Fig. 36 A) [Pacific coast of Costa Rica]......................... C. gemmatus n. sp. - Pterygostomial region not prominent, not visible from dorsal view (Fig. 4 F). Fingers of major chela of large males relatively short, slightly curved (Fig. 36 I) [Pacific coast of Costa Rica to Ecuador]................................. C. longipes

Published as part of Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), pp. 1-182 in Zootaxa 4209 (1) on pages 13-14, DOI: 10.11646/zootaxa.4209.1.1, http://zenodo.org/record/272646