PART 1 GARTH : PACIFIC OXYRHYNCHA 353 



Anterolateral margin bearing usually four, sometimes three, spines 

 or lobes behind the orbit ; posterolateral margin sometimes having a spine 

 or tubercle. Rostral horns either pointed or truncate. (Rathbun) 



Range: Eastern Pacific from San Diego, California (locality sup- 

 posed correct), and Puerto Refugio, Angel de la Guarda Island, Gulf 

 of California, Mexico, to Guayaquil, Ecuador (extralimital), possibly 

 to Valparaiso, Chile (Mithrax, sp. indet.), including Revilla Gigedo 

 and Galapagos Islands. Western Atlantic from Cape Hatteras, North 

 Carolina, to Ilha Victoria, Sao Paulo, Brazil; Bermuda. Shore-160 fath- 

 oms. 



The writer departs from the time-honored synonymy for this char- 

 acteristically American genus, customarily attributed to Latreille (1817, 

 p. 23), on the advice of Dr. L. B. Holthuis, who points out in a personal 

 communication that the use by that author of the article in the phrase 

 "Les Mithrax Leach" makes of it a vernacular name, while the fact that 

 the name is plural, as indicated by the article, makes it unavailable 

 nomenclatorially. The first valid use of the name, then, was that of 

 Desmarest (1823) ; the earliest type designation that of Milne Edwards 

 (1837, pi. 27), the title of whose work expressly states that it is accom- 

 panied by engraved plates representing the types of all the genera. 



The same difficulty with vernacular names is encountered in any 

 attempt at a formal synonymy of the subdivisions of the genus. Thus the 

 "Mithrax transversaux" plus the Nemausa of A. Milne Edwards (1875) 

 form the subgenus Mithrax as presently constituted, while his "Mithrax 

 deprimes ou Mithracules" (exclusive of Teleophrys) comprise the sub- 

 genus Mithraculus as here recognized. 



Key to the Pacific Species of Mithrax 

 la. Carapace roughened to a greater or lesser extent by tubercles or 

 spinules, branchial sulci wanting. Intermediate orbital teeth 

 pointed or subtruncate, conspicuous . (Subgenus Mit hrax) 

 2a. Rostral horns acute and elongate 



3a. A proximal tubercle on outer surface of manus. Four 

 blunt anterolateral spines, with only the hepatic having 

 an auxiliary spine at base. Rostral horns of moderate 

 length. Male first pleopod with three subterminal folds, 



tip acute. Size large armatus 



3b. Outer surface of manus without a proximal tubercle. 

 Carapace with a lateral angle. Five lateral spines, the 

 last postlateral ; hepatic and first branchial spines sim- 

 ple. Rostral horns long. Male first pleopod with trun- 

 cate tip. Size small spinipes 



