326 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21 



Libinia mexicana Rathbun 

 Plate T, Figs. 4, 5; Plate 37, Fig. 1 



Libinia mexicana Rathbun, 1892, p. 242, pi. 31, fig. 3; 1925, p. 328, pi. 

 244, fig. 1. 



Type: Young male, holotype, U.S.N.M. No. 16072, length 13.5 

 mm, width 7.5 mm. 



Type locality: Off Shoal Point, near the mouth of the Colorado 

 River, Gulf of California, Mexico, 10.5 fathoms, Albatross station 3029. 



Localities subsequently reported: None. Known only from the type 

 locality and unique specimen above. 



Atlantic analogue: None. A Gulf of California endemic species hav- 

 ing as its cognate on the Pacific coast of Lower California the foregoing 

 Libinia setosa Lockington. 



Diagnosis: Carapace with 6 median and 1 hepatic spine. Rostrum 

 longer than in Libinia setosa, horizontal, channeled beneath. Only one 

 tooth on basal antennal article. Manus of adult male compressed, fingers 

 gaping broadly at base. Tip of male abdomen rounded. Male first pleopod 

 channeled to tip ; keel upstanding. 



Description: Since the original description is based upon an immature 

 (13 mm) male specimen, a complete description of a 65 mm male from 

 San Felipe, Gulf of California, is given. It will be found possible to 

 compare the Gulf of California species point by point by referring to 

 the description of its west coast of Lower California cognate, Libinia 

 setosa, as given by Rathbun (1925, p. 327). 



Carapace narrowly pyriform, its width less than its postfrontal length 

 by the distance from the anterior gastric spine or tubercle to the base of 

 the rostrum. Rostrum horizontal, considerably longer than broad, tubu- 

 lar, sides subparallel, tip emarginate, the two shallow teeth fringed with 

 hair, and forming with the coarse and hairy antenna an effective excur- 

 rent channel. 



Median spines six, two gastric, one genital, two cardiac, and one 

 intestinal ; a single spine on either side of anterior gastric spine. Two 

 marginal spines, one branchial, the other subhepatic; four dorsal bran- 

 chial spines, the posterior two forming a slightly curved horizontal line 

 with the anterior cardiac spine, the anterior two with the genital spine. 

 A prominent preocular spine. A single hepatic spine ; a subbranchial spine 

 below the epimeral suture. Two stout pterygostomian spines, the anterior 

 acute, the posterior blunt ; a blunt spine at anteroexternal angle of basal 

 segment, a small spine just behind the outer margin of that segment. 



