PART 1 garth: pacific oxyrhyncha 401 



M. triangulatus, which has spread via Mexican offshore islands to the 

 Galapagos. The dual role of the Gulf of California in speciation is ap- 

 parent: it at once serves as a point of origin of autochthonous species 

 and as a recipient of an overflow of Panamic species. 



Genus STENOGIONOPS Desmarest 



Stenocionops Desmarest, 1823, p. 266; 1825, p. 153. Guerin, 1825a, p. 



484. Rathbun, 1925, p. 448. 

 Pericera Latreille, 1825, p. 699; type: Cancer furcatus [by error, 

 fuscatus] Olivier, 1791 — Stenocionops furcata (Olivier), by mono- 

 typy; 1829, p. 58. Rathbun, 1892, p. 243. 

 Chorilibinia Lockington, 1877c, p. 69; type: C. angusta Lockington, 

 1877, by monotypy. 



Type: The Atlantic Maia taurus Lamarck, 1818 = Cancer furcatus 

 Olivier, 1791, type of Stenocionops Desmarest by monotypy. 



Description: Carapace subpyriform, rather convex, with dorsal sur- 

 face uneven, tuberculated or spinous ; lateral margins armed with a series 

 of long spines ; preocular spine well developed. Rostrum composed of 

 two strong spines not deflexed and divergent from base; orbits tubular, 

 not strongly projecting ; eyes small, retractile within orbits. Basal antennal 

 article considerably enlarged, armed with one or two small distal spines 

 or tubercles not visible in a dorsal view. The merus of outer maxillipeds 

 with distal margin truncate, anterointernal angle emarginate, anteroex- 

 ternal angle rounded or subacute. 



Chelipeds in adult male well developed ; palm elongate and subcylin- 

 drical or somewhat compressed, not dilated or enlarged; fingers either 

 with no or with a moderate intermarginal hiatus at the base when 

 closed. Ambulatory legs moderately elongated, with articles subcylindri- 

 cal, without spines; dactyli nearly straight. 



Abdomen in male distinctly seven-segmented. (Rathbun, 1925) 



Range: Eastern Pacific from Abreojos Point, Lower California, and 

 Rocky Point, Gulf of California, Mexico, to Santa Elena Bay, Ecuador; 

 Galapagos Islands. Western Atlantic from Cape Hatteras, North Caro- 

 lina, to Rio de Janeiro, Brazil. Occurs also off West Africa. Shore-150 

 fathoms. 



Key to the Pacific Species of Stenocionops 

 la. Rostral horns straight, either long and widely divergent, or 

 short and closely approximated, but always closest together at 

 bases 



