PART 1 GARTH : PACIFIC OXYRHYNCHA 403 



Diagnosis: Rostral horns curved, contiguous medially, divergent an- 

 teriorly. Three lateral marginal spines, one hepatic, two branchial. Four 

 median dorsal spines. One strong basal antennal spine. Tip of male first 

 pleopod semicylindrical, grooved, doubling back limply; keel narrowly 

 acuminate. 



Description: Carapace oblong-ovate, narrower at the orbits than 

 posteriorly ; pubescent ; armed with three lateral spines, one hepatic, two 

 branchial. Protuberances of the dorsal surface partially concealed and 

 arranged as follows: Three sharp tubercles in a triangle on the gastric 

 region, the posterior one median and highest. On each branchial region 

 two spines or a spine and a tubercle in an oblique line with the postero- 

 lateral marginal spine, and a sharp tubercle close to the posterolateral 

 border of the cardiac region. Above the posterior margin a median spine, 

 and in front of it and on either side a tubercle, often sharp. The cardiac 

 region either smoothly rounded or surmounted by a sharp spine; occa- 

 sionally a spine, large in the old, near the anterior border of the branchial 

 region. Rostral horns curved, contiguous in the middle, separated at 

 base by a buttonhole slit, terminal halves or less moderately divergent. 

 Preocular spine prominent, long pointed ; postocular acute. Basal article 

 of antenna broad, armed with one long triangular spine, parallel with the 

 preocular spine and visible in dorsal view. 



Chelipeds of medium-sized male a little longer than the carapace and 

 the next pair of legs. In large males the chelipeds much more elongate. 

 Merus armed with five or six stout spines above. In small specimens the 

 ambulatory legs diminishing fairly regularly in length from the first to 

 the last, but in the larger males the first leg very much longer than the 

 second. (Rathbun, 1892, 1925, modified, of Stenocionops contigua) 



The proportionate length of the rostral horns is greater in young 

 than in adults, males of 33 mm and less having a slender, elongate 

 appearance. The degree of curvature of the opposed and divergent rostral 

 horns may vary from nearly parallel to widely arching. While dorsal 

 spines are usually absent, they are well developed in a male and female 

 of 16 and 20 mm, respectively. A 40.6 mm female has two hepatic spines 

 like Stenocionops macdonaldi (=S. ovata). A 34.8 mm female, perfect 

 in every other respect, lacks the right lateral spine. 



Material examined: 38 specimens from 26 Hancock stations. (See 

 Table 84) From off Rocky Point, Sonora, to San Lorenzo Channel in 

 the Gulf of California, and from Magdalena and Almejas Bays, west 

 coast of Lower California, Mexico. 



