PART 1 GARTH : PACIFIC OXYRHYNCHA 327 



Chelipeds considerably longer than ambulatory legs, stout, finely 

 granulate ; palm widening appreciably towards fingers ; dactyls two-thirds 

 as long as upper margin of palm ; fingers gaping widely in basal half. 

 Legs stout and rather short ; the dactyli, however, long, as in the related 

 species. 



Male abdomen with seven free segments, widest opposite segment 

 three, narrowing abruptly ; sides remaining subparallel to base of termi- 

 nal segment, this segment broadly rounded. Male first pleopod with a 

 slender, curving, grooved tip, sides of channel overlapping, keel arising 

 from a broad base set well back, narrowing toward tip, sparsely and 

 minutely spinulous. (See Plate T, figs. 4, 5) 



The 59 mm female from San Felipe resembles the male as regards 

 shape and tuberculatum of the carapace, except that the intestinal tubercle 

 is wanting. There is a supplementary anterior branchial tubercle lacking 

 in the male. In the absence of pile, deeply eroded pits are revealed out- 

 lining the gastric, cardiac, and intestinal regions and delimiting them 

 laterally from the hepatic and branchial. The rostrum is broken and the 

 antennae are missing, so that it is not possible to compare its length to 

 that of the male. The chelipeds are no more stout than the walking 

 legs ; the chelae, however, are of proportionate size and not filiform, as 

 in Libinia rostrata. The abdomen, which consists of seven separate seg- 

 ments, is ovoid in shape. 



The principal differences from Libinia setosa, then, will be found 

 in the more slender carapace and longer rostrum of L. mexicana, the 

 reduction in the number of median spines from eight to six by the 

 elimination of two of the gastric spines, the possession of but one instead 

 of two hepatic spines, a longitudinally more compressed cheliped with a 

 wider gape between the fingers in the male (a character which may be 

 expected to vary greatly with the maturity of the individual), and a 

 rounded terminal abdominal segment, that of L. setosa being triangular. 



Material examined: 11 specimens from 6 stations, all in the Gulf of 

 California. (See Table 67) From Rocky Point, Sonora, to San Ignacio 

 Bay, Sinaloa, Mexico. 



Measurements: Largest specimen, the male from San Felipe: length 



65.6 mm, width 48.7 mm, rostrum 10.0 mm, width 5.0 mm, cheliped 



96.7 mm, chela 43 mm, dactyl 17.3 mm, height of palm 10.8 mm, 

 ambulatory legs 97, 64, 60, and 50 mm, respectively. Female from San 

 Felipe: length 59.6 mm, width 45.6 mm, cheliped 56 mm. (Note: 

 Because of the rigidity of these specimens, measurements of cheliped and 



