46 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.18 



Peraeopod 5 : lower edge of posterior lobe of article 2 broadly trun- 

 cate, reaching down almost to middle of article 4; article 4 slightly 

 longer than 3, produced behind into a large, setose, tumid lobe; article 

 5 very short ; article 6 long, expanded ; article 7 rather slender. 



Uropod 1 reaching as far back as uropod 2 ; rami as long as peduncle ; 

 base of inner ramus with a single spine. 



Uropod 2: rami equal in length to peduncle; apices of both rami 

 armed with a single long spine, inner edge of inner ramus and outer 

 edge of outer ramus lined with spines. 



Uropod 3 : rami slender, lanceolate, outer ramus much more slender 

 than inner. 



Telson rather narrow, apices laterally notched, surface of each lobe 

 with 3 setae. 



Pleon segment 3 : posterior edge convex, lower posterior corner 

 strongly produced into a tooth, above which there is a sinus. 



Pleon segment 4 slightly elevated and weakly saddle-shaped. 



Pleon segment 6: lateral ridges strongly developed. 



Male: Unknown. 



Types: Holotype, AHF no. 3911, ovigerous female, 4.5 mm; para- 

 type, female, 5.0 mm. 



Type locality : Station 964-39, Tenacatita Bay, Mexico, 2 to 8 fms. 



Material examined: Stations 259-34 (3), 281-34 (5), 373-35 (1), 

 475-35 (6), 481-35 (1), 964-39 (6), 2026-51 (3). 



Remarks: This species appears closely related to A. gnathia, new 

 species, of which only the male is known. However, A. mexicana differs 

 in the shape of the head, in the larger lobe of article 4 of peraeopod 5, 

 in the unnotched anterior edge of article 5, and in a number of other 

 characters which may be seen from examination of the figures. It re- 

 sembles A. gnathia, particularly in the shape of gnathopod 1, pleon seg- 

 ments 3 and 6, and the telson. 



Distribution: Lower California at Cedros Island, and Santa Maria 

 Bay, 16 to 30 fms; Tangola Tangola Bay and Tenacatita Bay, Mexico, 

 2 to 20 fms; Salinas Bay, Costa Rica, 6 to 20 fms; off Viejas Islands, 

 Independicia Bay, Peru, 12 fms. 



Ampelisca gnathia, new species 

 Plates 33 and 34 



Description of male: Head about as long as first 3 body segments, 

 superior edge prolonged anteriorly to form a blunt rostrum, anterior 



