PART 1 GARTH : PACIFIC OXYRHYNCHA 367 



mexicanus) . Galapagos Islands, Ecuador: Hood Island, Arcturus 

 (Boone) ; Charles Island, A. Wollebaek (Sivertsen) ; Albemarle Island, 

 and to 160 fathoms, Velero III (Garth). 



Atlantic analogue: Mithrax (Mithrax) acuticornis Stimpson. 



Diagnosis: Rostral horns long and divergent. Five lateral spines, the 

 last postlateral ; hepatic and first branchial spines single. A pair of meso- 

 gastric spines or spinules. Tip of male first pleopod truncate. A small 

 species. 



Description: Carapace pyriform, tumid, setose, much longer than 

 wide ; lateral margins without an angle. Six median spines, none very 

 prominent, except the posterior marginal spine. Of the five anterolateral 

 spines the hepatic the most prominent, the other four being small ; a 

 subhepatic spinule; a prominent posterolateral spine, about half the size 

 of the hepatic spine, located above the level of the anterolateral spines ; 

 a pair of epibranchial spines paralleling the anterolateral spines; a pair 

 of spines on the metabranchial region paralleling the anterolateral mar- 

 gin. Rostral horns nearly one-fourth the body length, diverging, regu- 

 larly tapering. Suborbital margin armed with two spines, the median 

 large, the distal largest and prominent in dorsal view; supraorbital 

 margin having three spines, postorbital, preorbital, and median, the latter 

 the smallest. Antennae nearly as long as the width of the carapace. 

 Buccal area widest anteriorly. 



Chelipeds small, not as long as the first ambulatory leg; merus with 

 a spine at upper distal end, another just proximal to this; carpus with 

 three or four small dull spines; hands smooth, cylindrical; fingers not 

 gaping. 



. First ambulatory leg nearly as long as the carapace; legs tomentose 

 and setose ; merus armed with a distal spine on upper carpal articulation. 



Terminal segment of abdomen longer than wide, sides converging, 

 tip arcuate; not as wide as penultimate segment. (Glassell, modified, of 

 Mithrax (Mithrax) mexicanus) 



In the very young a series of spinules replaces the five lateral spines, 

 the lateral angle is not apparent, and the paired mesogastric spinules 

 may be wanting. The male first pleopod examined was from a 15 mm 

 specimen. 



Material examined: Three specimens from as many stations. (See 

 Table 76) From the southern part of the Gulf of California, Mexico, 

 and from Cocos Island, Costa Rica. In addition to the above, 3 speci- 

 mens from 3 Galapagos Islands stations (Garth, 1946), plus 1 male 

 from Gardner Bay, Hood Island, 25-35 -£athoms, station 201-34, not 

 recorded. 



